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/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent.locks;
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import java.util.concurrent.*;
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import java.util.concurrent.atomic.*;
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import java.util.*;
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/**
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* An implementation of {@link ReadWriteLock} supporting similar
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* semantics to {@link ReentrantLock}.
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* <p>This class has the following properties:
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*
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* <ul>
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* <li><b>Acquisition order</b>
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*
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* <p> This class does not impose a reader or writer preference
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* ordering for lock access. However, it does support an optional
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* <em>fairness</em> policy.
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*
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* <dl>
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* <dt><b><i>Non-fair mode (default)</i></b>
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* <dd>When constructed as non-fair (the default), the order of entry
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* to the read and write lock is unspecified, subject to reentrancy
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* constraints. A nonfair lock that is continuously contended may
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* indefinitely postpone one or more reader or writer threads, but
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* will normally have higher throughput than a fair lock.
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* <p>
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*
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* <dt><b><i>Fair mode</i></b>
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* <dd> When constructed as fair, threads contend for entry using an
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* approximately arrival-order policy. When the currently held lock
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* is released either the longest-waiting single writer thread will
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* be assigned the write lock, or if there is a group of reader threads
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* waiting longer than all waiting writer threads, that group will be
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* assigned the read lock.
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*
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* <p>A thread that tries to acquire a fair read lock (non-reentrantly)
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* will block if either the write lock is held, or there is a waiting
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* writer thread. The thread will not acquire the read lock until
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* after the oldest currently waiting writer thread has acquired and
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* released the write lock. Of course, if a waiting writer abandons
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* its wait, leaving one or more reader threads as the longest waiters
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* in the queue with the write lock free, then those readers will be
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* assigned the read lock.
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*
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* <p>A thread that tries to acquire a fair write lock (non-reentrantly)
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* will block unless both the read lock and write lock are free (which
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* implies there are no waiting threads). (Note that the non-blocking
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* {@link ReadLock#tryLock()} and {@link WriteLock#tryLock()} methods
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* do not honor this fair setting and will acquire the lock if it is
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* possible, regardless of waiting threads.)
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* <p>
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* </dl>
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*
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* <li><b>Reentrancy</b>
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*
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* <p>This lock allows both readers and writers to reacquire read or
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* write locks in the style of a {@link ReentrantLock}. Non-reentrant
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* readers are not allowed until all write locks held by the writing
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* thread have been released.
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*
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* <p>Additionally, a writer can acquire the read lock, but not
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* vice-versa. Among other applications, reentrancy can be useful
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* when write locks are held during calls or callbacks to methods that
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* perform reads under read locks. If a reader tries to acquire the
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* write lock it will never succeed.
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*
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* <li><b>Lock downgrading</b>
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* <p>Reentrancy also allows downgrading from the write lock to a read lock,
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* by acquiring the write lock, then the read lock and then releasing the
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* write lock. However, upgrading from a read lock to the write lock is
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* <b>not</b> possible.
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*
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* <li><b>Interruption of lock acquisition</b>
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* <p>The read lock and write lock both support interruption during lock
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* acquisition.
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*
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* <li><b>{@link Condition} support</b>
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* <p>The write lock provides a {@link Condition} implementation that
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* behaves in the same way, with respect to the write lock, as the
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* {@link Condition} implementation provided by
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* {@link ReentrantLock#newCondition} does for {@link ReentrantLock}.
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* This {@link Condition} can, of course, only be used with the write lock.
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*
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* <p>The read lock does not support a {@link Condition} and
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* {@code readLock().newCondition()} throws
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* {@code UnsupportedOperationException}.
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*
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* <li><b>Instrumentation</b>
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* <p>This class supports methods to determine whether locks
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* are held or contended. These methods are designed for monitoring
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* system state, not for synchronization control.
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* </ul>
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*
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* <p>Serialization of this class behaves in the same way as built-in
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* locks: a deserialized lock is in the unlocked state, regardless of
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* its state when serialized.
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*
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* <p><b>Sample usages</b>. Here is a code sketch showing how to perform
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* lock downgrading after updating a cache (exception handling is
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* particularly tricky when handling multiple locks in a non-nested
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* fashion):
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*
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* <pre> {@code
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* class CachedData {
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* Object data;
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* volatile boolean cacheValid;
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* final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
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*
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* void processCachedData() {
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* rwl.readLock().lock();
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* if (!cacheValid) {
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* // Must release read lock before acquiring write lock
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* rwl.readLock().unlock();
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* rwl.writeLock().lock();
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* try {
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* // Recheck state because another thread might have
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* // acquired write lock and changed state before we did.
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* if (!cacheValid) {
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* data = ...
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* cacheValid = true;
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* }
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* // Downgrade by acquiring read lock before releasing write lock
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* rwl.readLock().lock();
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* } finally {
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* rwl.writeLock().unlock(); // Unlock write, still hold read
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* }
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* }
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*
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* try {
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* use(data);
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* } finally {
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* rwl.readLock().unlock();
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* }
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* }
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* }}</pre>
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*
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* ReentrantReadWriteLocks can be used to improve concurrency in some
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* uses of some kinds of Collections. This is typically worthwhile
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* only when the collections are expected to be large, accessed by
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* more reader threads than writer threads, and entail operations with
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* overhead that outweighs synchronization overhead. For example, here
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* is a class using a TreeMap that is expected to be large and
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* concurrently accessed.
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*
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* <pre>{@code
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* class RWDictionary {
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* private final Map<String, Data> m = new TreeMap<String, Data>();
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* private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
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* private final Lock r = rwl.readLock();
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* private final Lock w = rwl.writeLock();
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*
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* public Data get(String key) {
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* r.lock();
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* try { return m.get(key); }
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* finally { r.unlock(); }
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* }
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* public String[] allKeys() {
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* r.lock();
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* try { return m.keySet().toArray(); }
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* finally { r.unlock(); }
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* }
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* public Data put(String key, Data value) {
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* w.lock();
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* try { return m.put(key, value); }
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* finally { w.unlock(); }
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* }
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* public void clear() {
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* w.lock();
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* try { m.clear(); }
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* finally { w.unlock(); }
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* }
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* }}</pre>
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*
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* <h3>Implementation Notes</h3>
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*
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* <p>This lock supports a maximum of 65535 recursive write locks
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* and 65535 read locks. Attempts to exceed these limits result in
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* {@link Error} throws from locking methods.
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*
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* @since 1.5
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* @author Doug Lea
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*
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*/
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public class ReentrantReadWriteLock
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implements ReadWriteLock, java.io.Serializable {
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private static final long serialVersionUID = -6992448646407690164L;
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/** Inner class providing readlock */
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private final ReentrantReadWriteLock.ReadLock readerLock;
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/** Inner class providing writelock */
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private final ReentrantReadWriteLock.WriteLock writerLock;
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/** Performs all synchronization mechanics */
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final Sync sync;
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/**
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* Creates a new {@code ReentrantReadWriteLock} with
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* default (nonfair) ordering properties.
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*/
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public ReentrantReadWriteLock() {
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this(false);
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}
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/**
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* Creates a new {@code ReentrantReadWriteLock} with
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* the given fairness policy.
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*
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* @param fair {@code true} if this lock should use a fair ordering policy
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*/
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public ReentrantReadWriteLock(boolean fair) {
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sync = fair ? new FairSync() : new NonfairSync();
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readerLock = new ReadLock(this);
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writerLock = new WriteLock(this);
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}
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public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
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public ReentrantReadWriteLock.ReadLock readLock() { return readerLock; }
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/**
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* Synchronization implementation for ReentrantReadWriteLock.
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* Subclassed into fair and nonfair versions.
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*/
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abstract static class Sync extends AbstractQueuedSynchronizer {
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private static final long serialVersionUID = 6317671515068378041L;
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/*
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* Read vs write count extraction constants and functions.
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* Lock state is logically divided into two unsigned shorts:
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* The lower one representing the exclusive (writer) lock hold count,
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* and the upper the shared (reader) hold count.
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*/
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static final int SHARED_SHIFT = 16;
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static final int SHARED_UNIT = (1 << SHARED_SHIFT);
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static final int MAX_COUNT = (1 << SHARED_SHIFT) - 1;
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static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
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/** Returns the number of shared holds represented in count */
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static int sharedCount(int c) { return c >>> SHARED_SHIFT; }
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/** Returns the number of exclusive holds represented in count */
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static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }
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/**
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* A counter for per-thread read hold counts.
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* Maintained as a ThreadLocal; cached in cachedHoldCounter
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*/
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static final class HoldCounter {
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int count = 0;
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// Use id, not reference, to avoid garbage retention
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final long tid = Thread.currentThread().getId();
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}
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/**
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* ThreadLocal subclass. Easiest to explicitly define for sake
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* of deserialization mechanics.
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*/
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static final class ThreadLocalHoldCounter
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extends ThreadLocal<HoldCounter> {
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public HoldCounter initialValue() {
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return new HoldCounter();
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}
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}
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/**
|
jaroslav@1890
|
297 |
* The number of reentrant read locks held by current thread.
|
jaroslav@1890
|
298 |
* Initialized only in constructor and readObject.
|
jaroslav@1890
|
299 |
* Removed whenever a thread's read hold count drops to 0.
|
jaroslav@1890
|
300 |
*/
|
jaroslav@1890
|
301 |
private transient ThreadLocalHoldCounter readHolds;
|
jaroslav@1890
|
302 |
|
jaroslav@1890
|
303 |
/**
|
jaroslav@1890
|
304 |
* The hold count of the last thread to successfully acquire
|
jaroslav@1890
|
305 |
* readLock. This saves ThreadLocal lookup in the common case
|
jaroslav@1890
|
306 |
* where the next thread to release is the last one to
|
jaroslav@1890
|
307 |
* acquire. This is non-volatile since it is just used
|
jaroslav@1890
|
308 |
* as a heuristic, and would be great for threads to cache.
|
jaroslav@1890
|
309 |
*
|
jaroslav@1890
|
310 |
* <p>Can outlive the Thread for which it is caching the read
|
jaroslav@1890
|
311 |
* hold count, but avoids garbage retention by not retaining a
|
jaroslav@1890
|
312 |
* reference to the Thread.
|
jaroslav@1890
|
313 |
*
|
jaroslav@1890
|
314 |
* <p>Accessed via a benign data race; relies on the memory
|
jaroslav@1890
|
315 |
* model's final field and out-of-thin-air guarantees.
|
jaroslav@1890
|
316 |
*/
|
jaroslav@1890
|
317 |
private transient HoldCounter cachedHoldCounter;
|
jaroslav@1890
|
318 |
|
jaroslav@1890
|
319 |
/**
|
jaroslav@1890
|
320 |
* firstReader is the first thread to have acquired the read lock.
|
jaroslav@1890
|
321 |
* firstReaderHoldCount is firstReader's hold count.
|
jaroslav@1890
|
322 |
*
|
jaroslav@1890
|
323 |
* <p>More precisely, firstReader is the unique thread that last
|
jaroslav@1890
|
324 |
* changed the shared count from 0 to 1, and has not released the
|
jaroslav@1890
|
325 |
* read lock since then; null if there is no such thread.
|
jaroslav@1890
|
326 |
*
|
jaroslav@1890
|
327 |
* <p>Cannot cause garbage retention unless the thread terminated
|
jaroslav@1890
|
328 |
* without relinquishing its read locks, since tryReleaseShared
|
jaroslav@1890
|
329 |
* sets it to null.
|
jaroslav@1890
|
330 |
*
|
jaroslav@1890
|
331 |
* <p>Accessed via a benign data race; relies on the memory
|
jaroslav@1890
|
332 |
* model's out-of-thin-air guarantees for references.
|
jaroslav@1890
|
333 |
*
|
jaroslav@1890
|
334 |
* <p>This allows tracking of read holds for uncontended read
|
jaroslav@1890
|
335 |
* locks to be very cheap.
|
jaroslav@1890
|
336 |
*/
|
jaroslav@1890
|
337 |
private transient Thread firstReader = null;
|
jaroslav@1890
|
338 |
private transient int firstReaderHoldCount;
|
jaroslav@1890
|
339 |
|
jaroslav@1890
|
340 |
Sync() {
|
jaroslav@1890
|
341 |
readHolds = new ThreadLocalHoldCounter();
|
jaroslav@1890
|
342 |
setState(getState()); // ensures visibility of readHolds
|
jaroslav@1890
|
343 |
}
|
jaroslav@1890
|
344 |
|
jaroslav@1890
|
345 |
/*
|
jaroslav@1890
|
346 |
* Acquires and releases use the same code for fair and
|
jaroslav@1890
|
347 |
* nonfair locks, but differ in whether/how they allow barging
|
jaroslav@1890
|
348 |
* when queues are non-empty.
|
jaroslav@1890
|
349 |
*/
|
jaroslav@1890
|
350 |
|
jaroslav@1890
|
351 |
/**
|
jaroslav@1890
|
352 |
* Returns true if the current thread, when trying to acquire
|
jaroslav@1890
|
353 |
* the read lock, and otherwise eligible to do so, should block
|
jaroslav@1890
|
354 |
* because of policy for overtaking other waiting threads.
|
jaroslav@1890
|
355 |
*/
|
jaroslav@1890
|
356 |
abstract boolean readerShouldBlock();
|
jaroslav@1890
|
357 |
|
jaroslav@1890
|
358 |
/**
|
jaroslav@1890
|
359 |
* Returns true if the current thread, when trying to acquire
|
jaroslav@1890
|
360 |
* the write lock, and otherwise eligible to do so, should block
|
jaroslav@1890
|
361 |
* because of policy for overtaking other waiting threads.
|
jaroslav@1890
|
362 |
*/
|
jaroslav@1890
|
363 |
abstract boolean writerShouldBlock();
|
jaroslav@1890
|
364 |
|
jaroslav@1890
|
365 |
/*
|
jaroslav@1890
|
366 |
* Note that tryRelease and tryAcquire can be called by
|
jaroslav@1890
|
367 |
* Conditions. So it is possible that their arguments contain
|
jaroslav@1890
|
368 |
* both read and write holds that are all released during a
|
jaroslav@1890
|
369 |
* condition wait and re-established in tryAcquire.
|
jaroslav@1890
|
370 |
*/
|
jaroslav@1890
|
371 |
|
jaroslav@1890
|
372 |
protected final boolean tryRelease(int releases) {
|
jaroslav@1890
|
373 |
if (!isHeldExclusively())
|
jaroslav@1890
|
374 |
throw new IllegalMonitorStateException();
|
jaroslav@1890
|
375 |
int nextc = getState() - releases;
|
jaroslav@1890
|
376 |
boolean free = exclusiveCount(nextc) == 0;
|
jaroslav@1890
|
377 |
if (free)
|
jaroslav@1890
|
378 |
setExclusiveOwnerThread(null);
|
jaroslav@1890
|
379 |
setState(nextc);
|
jaroslav@1890
|
380 |
return free;
|
jaroslav@1890
|
381 |
}
|
jaroslav@1890
|
382 |
|
jaroslav@1890
|
383 |
protected final boolean tryAcquire(int acquires) {
|
jaroslav@1890
|
384 |
/*
|
jaroslav@1890
|
385 |
* Walkthrough:
|
jaroslav@1890
|
386 |
* 1. If read count nonzero or write count nonzero
|
jaroslav@1890
|
387 |
* and owner is a different thread, fail.
|
jaroslav@1890
|
388 |
* 2. If count would saturate, fail. (This can only
|
jaroslav@1890
|
389 |
* happen if count is already nonzero.)
|
jaroslav@1890
|
390 |
* 3. Otherwise, this thread is eligible for lock if
|
jaroslav@1890
|
391 |
* it is either a reentrant acquire or
|
jaroslav@1890
|
392 |
* queue policy allows it. If so, update state
|
jaroslav@1890
|
393 |
* and set owner.
|
jaroslav@1890
|
394 |
*/
|
jaroslav@1890
|
395 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
396 |
int c = getState();
|
jaroslav@1890
|
397 |
int w = exclusiveCount(c);
|
jaroslav@1890
|
398 |
if (c != 0) {
|
jaroslav@1890
|
399 |
// (Note: if c != 0 and w == 0 then shared count != 0)
|
jaroslav@1890
|
400 |
if (w == 0 || current != getExclusiveOwnerThread())
|
jaroslav@1890
|
401 |
return false;
|
jaroslav@1890
|
402 |
if (w + exclusiveCount(acquires) > MAX_COUNT)
|
jaroslav@1890
|
403 |
throw new Error("Maximum lock count exceeded");
|
jaroslav@1890
|
404 |
// Reentrant acquire
|
jaroslav@1890
|
405 |
setState(c + acquires);
|
jaroslav@1890
|
406 |
return true;
|
jaroslav@1890
|
407 |
}
|
jaroslav@1890
|
408 |
if (writerShouldBlock() ||
|
jaroslav@1890
|
409 |
!compareAndSetState(c, c + acquires))
|
jaroslav@1890
|
410 |
return false;
|
jaroslav@1890
|
411 |
setExclusiveOwnerThread(current);
|
jaroslav@1890
|
412 |
return true;
|
jaroslav@1890
|
413 |
}
|
jaroslav@1890
|
414 |
|
jaroslav@1890
|
415 |
protected final boolean tryReleaseShared(int unused) {
|
jaroslav@1890
|
416 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
417 |
if (firstReader == current) {
|
jaroslav@1890
|
418 |
// assert firstReaderHoldCount > 0;
|
jaroslav@1890
|
419 |
if (firstReaderHoldCount == 1)
|
jaroslav@1890
|
420 |
firstReader = null;
|
jaroslav@1890
|
421 |
else
|
jaroslav@1890
|
422 |
firstReaderHoldCount--;
|
jaroslav@1890
|
423 |
} else {
|
jaroslav@1890
|
424 |
HoldCounter rh = cachedHoldCounter;
|
jaroslav@1890
|
425 |
if (rh == null || rh.tid != current.getId())
|
jaroslav@1890
|
426 |
rh = readHolds.get();
|
jaroslav@1890
|
427 |
int count = rh.count;
|
jaroslav@1890
|
428 |
if (count <= 1) {
|
jaroslav@1890
|
429 |
readHolds.remove();
|
jaroslav@1890
|
430 |
if (count <= 0)
|
jaroslav@1890
|
431 |
throw unmatchedUnlockException();
|
jaroslav@1890
|
432 |
}
|
jaroslav@1890
|
433 |
--rh.count;
|
jaroslav@1890
|
434 |
}
|
jaroslav@1890
|
435 |
for (;;) {
|
jaroslav@1890
|
436 |
int c = getState();
|
jaroslav@1890
|
437 |
int nextc = c - SHARED_UNIT;
|
jaroslav@1890
|
438 |
if (compareAndSetState(c, nextc))
|
jaroslav@1890
|
439 |
// Releasing the read lock has no effect on readers,
|
jaroslav@1890
|
440 |
// but it may allow waiting writers to proceed if
|
jaroslav@1890
|
441 |
// both read and write locks are now free.
|
jaroslav@1890
|
442 |
return nextc == 0;
|
jaroslav@1890
|
443 |
}
|
jaroslav@1890
|
444 |
}
|
jaroslav@1890
|
445 |
|
jaroslav@1890
|
446 |
private IllegalMonitorStateException unmatchedUnlockException() {
|
jaroslav@1890
|
447 |
return new IllegalMonitorStateException(
|
jaroslav@1890
|
448 |
"attempt to unlock read lock, not locked by current thread");
|
jaroslav@1890
|
449 |
}
|
jaroslav@1890
|
450 |
|
jaroslav@1890
|
451 |
protected final int tryAcquireShared(int unused) {
|
jaroslav@1890
|
452 |
/*
|
jaroslav@1890
|
453 |
* Walkthrough:
|
jaroslav@1890
|
454 |
* 1. If write lock held by another thread, fail.
|
jaroslav@1890
|
455 |
* 2. Otherwise, this thread is eligible for
|
jaroslav@1890
|
456 |
* lock wrt state, so ask if it should block
|
jaroslav@1890
|
457 |
* because of queue policy. If not, try
|
jaroslav@1890
|
458 |
* to grant by CASing state and updating count.
|
jaroslav@1890
|
459 |
* Note that step does not check for reentrant
|
jaroslav@1890
|
460 |
* acquires, which is postponed to full version
|
jaroslav@1890
|
461 |
* to avoid having to check hold count in
|
jaroslav@1890
|
462 |
* the more typical non-reentrant case.
|
jaroslav@1890
|
463 |
* 3. If step 2 fails either because thread
|
jaroslav@1890
|
464 |
* apparently not eligible or CAS fails or count
|
jaroslav@1890
|
465 |
* saturated, chain to version with full retry loop.
|
jaroslav@1890
|
466 |
*/
|
jaroslav@1890
|
467 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
468 |
int c = getState();
|
jaroslav@1890
|
469 |
if (exclusiveCount(c) != 0 &&
|
jaroslav@1890
|
470 |
getExclusiveOwnerThread() != current)
|
jaroslav@1890
|
471 |
return -1;
|
jaroslav@1890
|
472 |
int r = sharedCount(c);
|
jaroslav@1890
|
473 |
if (!readerShouldBlock() &&
|
jaroslav@1890
|
474 |
r < MAX_COUNT &&
|
jaroslav@1890
|
475 |
compareAndSetState(c, c + SHARED_UNIT)) {
|
jaroslav@1890
|
476 |
if (r == 0) {
|
jaroslav@1890
|
477 |
firstReader = current;
|
jaroslav@1890
|
478 |
firstReaderHoldCount = 1;
|
jaroslav@1890
|
479 |
} else if (firstReader == current) {
|
jaroslav@1890
|
480 |
firstReaderHoldCount++;
|
jaroslav@1890
|
481 |
} else {
|
jaroslav@1890
|
482 |
HoldCounter rh = cachedHoldCounter;
|
jaroslav@1890
|
483 |
if (rh == null || rh.tid != current.getId())
|
jaroslav@1890
|
484 |
cachedHoldCounter = rh = readHolds.get();
|
jaroslav@1890
|
485 |
else if (rh.count == 0)
|
jaroslav@1890
|
486 |
readHolds.set(rh);
|
jaroslav@1890
|
487 |
rh.count++;
|
jaroslav@1890
|
488 |
}
|
jaroslav@1890
|
489 |
return 1;
|
jaroslav@1890
|
490 |
}
|
jaroslav@1890
|
491 |
return fullTryAcquireShared(current);
|
jaroslav@1890
|
492 |
}
|
jaroslav@1890
|
493 |
|
jaroslav@1890
|
494 |
/**
|
jaroslav@1890
|
495 |
* Full version of acquire for reads, that handles CAS misses
|
jaroslav@1890
|
496 |
* and reentrant reads not dealt with in tryAcquireShared.
|
jaroslav@1890
|
497 |
*/
|
jaroslav@1890
|
498 |
final int fullTryAcquireShared(Thread current) {
|
jaroslav@1890
|
499 |
/*
|
jaroslav@1890
|
500 |
* This code is in part redundant with that in
|
jaroslav@1890
|
501 |
* tryAcquireShared but is simpler overall by not
|
jaroslav@1890
|
502 |
* complicating tryAcquireShared with interactions between
|
jaroslav@1890
|
503 |
* retries and lazily reading hold counts.
|
jaroslav@1890
|
504 |
*/
|
jaroslav@1890
|
505 |
HoldCounter rh = null;
|
jaroslav@1890
|
506 |
for (;;) {
|
jaroslav@1890
|
507 |
int c = getState();
|
jaroslav@1890
|
508 |
if (exclusiveCount(c) != 0) {
|
jaroslav@1890
|
509 |
if (getExclusiveOwnerThread() != current)
|
jaroslav@1890
|
510 |
return -1;
|
jaroslav@1890
|
511 |
// else we hold the exclusive lock; blocking here
|
jaroslav@1890
|
512 |
// would cause deadlock.
|
jaroslav@1890
|
513 |
} else if (readerShouldBlock()) {
|
jaroslav@1890
|
514 |
// Make sure we're not acquiring read lock reentrantly
|
jaroslav@1890
|
515 |
if (firstReader == current) {
|
jaroslav@1890
|
516 |
// assert firstReaderHoldCount > 0;
|
jaroslav@1890
|
517 |
} else {
|
jaroslav@1890
|
518 |
if (rh == null) {
|
jaroslav@1890
|
519 |
rh = cachedHoldCounter;
|
jaroslav@1890
|
520 |
if (rh == null || rh.tid != current.getId()) {
|
jaroslav@1890
|
521 |
rh = readHolds.get();
|
jaroslav@1890
|
522 |
if (rh.count == 0)
|
jaroslav@1890
|
523 |
readHolds.remove();
|
jaroslav@1890
|
524 |
}
|
jaroslav@1890
|
525 |
}
|
jaroslav@1890
|
526 |
if (rh.count == 0)
|
jaroslav@1890
|
527 |
return -1;
|
jaroslav@1890
|
528 |
}
|
jaroslav@1890
|
529 |
}
|
jaroslav@1890
|
530 |
if (sharedCount(c) == MAX_COUNT)
|
jaroslav@1890
|
531 |
throw new Error("Maximum lock count exceeded");
|
jaroslav@1890
|
532 |
if (compareAndSetState(c, c + SHARED_UNIT)) {
|
jaroslav@1890
|
533 |
if (sharedCount(c) == 0) {
|
jaroslav@1890
|
534 |
firstReader = current;
|
jaroslav@1890
|
535 |
firstReaderHoldCount = 1;
|
jaroslav@1890
|
536 |
} else if (firstReader == current) {
|
jaroslav@1890
|
537 |
firstReaderHoldCount++;
|
jaroslav@1890
|
538 |
} else {
|
jaroslav@1890
|
539 |
if (rh == null)
|
jaroslav@1890
|
540 |
rh = cachedHoldCounter;
|
jaroslav@1890
|
541 |
if (rh == null || rh.tid != current.getId())
|
jaroslav@1890
|
542 |
rh = readHolds.get();
|
jaroslav@1890
|
543 |
else if (rh.count == 0)
|
jaroslav@1890
|
544 |
readHolds.set(rh);
|
jaroslav@1890
|
545 |
rh.count++;
|
jaroslav@1890
|
546 |
cachedHoldCounter = rh; // cache for release
|
jaroslav@1890
|
547 |
}
|
jaroslav@1890
|
548 |
return 1;
|
jaroslav@1890
|
549 |
}
|
jaroslav@1890
|
550 |
}
|
jaroslav@1890
|
551 |
}
|
jaroslav@1890
|
552 |
|
jaroslav@1890
|
553 |
/**
|
jaroslav@1890
|
554 |
* Performs tryLock for write, enabling barging in both modes.
|
jaroslav@1890
|
555 |
* This is identical in effect to tryAcquire except for lack
|
jaroslav@1890
|
556 |
* of calls to writerShouldBlock.
|
jaroslav@1890
|
557 |
*/
|
jaroslav@1890
|
558 |
final boolean tryWriteLock() {
|
jaroslav@1890
|
559 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
560 |
int c = getState();
|
jaroslav@1890
|
561 |
if (c != 0) {
|
jaroslav@1890
|
562 |
int w = exclusiveCount(c);
|
jaroslav@1890
|
563 |
if (w == 0 || current != getExclusiveOwnerThread())
|
jaroslav@1890
|
564 |
return false;
|
jaroslav@1890
|
565 |
if (w == MAX_COUNT)
|
jaroslav@1890
|
566 |
throw new Error("Maximum lock count exceeded");
|
jaroslav@1890
|
567 |
}
|
jaroslav@1890
|
568 |
if (!compareAndSetState(c, c + 1))
|
jaroslav@1890
|
569 |
return false;
|
jaroslav@1890
|
570 |
setExclusiveOwnerThread(current);
|
jaroslav@1890
|
571 |
return true;
|
jaroslav@1890
|
572 |
}
|
jaroslav@1890
|
573 |
|
jaroslav@1890
|
574 |
/**
|
jaroslav@1890
|
575 |
* Performs tryLock for read, enabling barging in both modes.
|
jaroslav@1890
|
576 |
* This is identical in effect to tryAcquireShared except for
|
jaroslav@1890
|
577 |
* lack of calls to readerShouldBlock.
|
jaroslav@1890
|
578 |
*/
|
jaroslav@1890
|
579 |
final boolean tryReadLock() {
|
jaroslav@1890
|
580 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
581 |
for (;;) {
|
jaroslav@1890
|
582 |
int c = getState();
|
jaroslav@1890
|
583 |
if (exclusiveCount(c) != 0 &&
|
jaroslav@1890
|
584 |
getExclusiveOwnerThread() != current)
|
jaroslav@1890
|
585 |
return false;
|
jaroslav@1890
|
586 |
int r = sharedCount(c);
|
jaroslav@1890
|
587 |
if (r == MAX_COUNT)
|
jaroslav@1890
|
588 |
throw new Error("Maximum lock count exceeded");
|
jaroslav@1890
|
589 |
if (compareAndSetState(c, c + SHARED_UNIT)) {
|
jaroslav@1890
|
590 |
if (r == 0) {
|
jaroslav@1890
|
591 |
firstReader = current;
|
jaroslav@1890
|
592 |
firstReaderHoldCount = 1;
|
jaroslav@1890
|
593 |
} else if (firstReader == current) {
|
jaroslav@1890
|
594 |
firstReaderHoldCount++;
|
jaroslav@1890
|
595 |
} else {
|
jaroslav@1890
|
596 |
HoldCounter rh = cachedHoldCounter;
|
jaroslav@1890
|
597 |
if (rh == null || rh.tid != current.getId())
|
jaroslav@1890
|
598 |
cachedHoldCounter = rh = readHolds.get();
|
jaroslav@1890
|
599 |
else if (rh.count == 0)
|
jaroslav@1890
|
600 |
readHolds.set(rh);
|
jaroslav@1890
|
601 |
rh.count++;
|
jaroslav@1890
|
602 |
}
|
jaroslav@1890
|
603 |
return true;
|
jaroslav@1890
|
604 |
}
|
jaroslav@1890
|
605 |
}
|
jaroslav@1890
|
606 |
}
|
jaroslav@1890
|
607 |
|
jaroslav@1890
|
608 |
protected final boolean isHeldExclusively() {
|
jaroslav@1890
|
609 |
// While we must in general read state before owner,
|
jaroslav@1890
|
610 |
// we don't need to do so to check if current thread is owner
|
jaroslav@1890
|
611 |
return getExclusiveOwnerThread() == Thread.currentThread();
|
jaroslav@1890
|
612 |
}
|
jaroslav@1890
|
613 |
|
jaroslav@1890
|
614 |
// Methods relayed to outer class
|
jaroslav@1890
|
615 |
|
jaroslav@1890
|
616 |
final ConditionObject newCondition() {
|
jaroslav@1890
|
617 |
return new ConditionObject();
|
jaroslav@1890
|
618 |
}
|
jaroslav@1890
|
619 |
|
jaroslav@1890
|
620 |
final Thread getOwner() {
|
jaroslav@1890
|
621 |
// Must read state before owner to ensure memory consistency
|
jaroslav@1890
|
622 |
return ((exclusiveCount(getState()) == 0) ?
|
jaroslav@1890
|
623 |
null :
|
jaroslav@1890
|
624 |
getExclusiveOwnerThread());
|
jaroslav@1890
|
625 |
}
|
jaroslav@1890
|
626 |
|
jaroslav@1890
|
627 |
final int getReadLockCount() {
|
jaroslav@1890
|
628 |
return sharedCount(getState());
|
jaroslav@1890
|
629 |
}
|
jaroslav@1890
|
630 |
|
jaroslav@1890
|
631 |
final boolean isWriteLocked() {
|
jaroslav@1890
|
632 |
return exclusiveCount(getState()) != 0;
|
jaroslav@1890
|
633 |
}
|
jaroslav@1890
|
634 |
|
jaroslav@1890
|
635 |
final int getWriteHoldCount() {
|
jaroslav@1890
|
636 |
return isHeldExclusively() ? exclusiveCount(getState()) : 0;
|
jaroslav@1890
|
637 |
}
|
jaroslav@1890
|
638 |
|
jaroslav@1890
|
639 |
final int getReadHoldCount() {
|
jaroslav@1890
|
640 |
if (getReadLockCount() == 0)
|
jaroslav@1890
|
641 |
return 0;
|
jaroslav@1890
|
642 |
|
jaroslav@1890
|
643 |
Thread current = Thread.currentThread();
|
jaroslav@1890
|
644 |
if (firstReader == current)
|
jaroslav@1890
|
645 |
return firstReaderHoldCount;
|
jaroslav@1890
|
646 |
|
jaroslav@1890
|
647 |
HoldCounter rh = cachedHoldCounter;
|
jaroslav@1890
|
648 |
if (rh != null && rh.tid == current.getId())
|
jaroslav@1890
|
649 |
return rh.count;
|
jaroslav@1890
|
650 |
|
jaroslav@1890
|
651 |
int count = readHolds.get().count;
|
jaroslav@1890
|
652 |
if (count == 0) readHolds.remove();
|
jaroslav@1890
|
653 |
return count;
|
jaroslav@1890
|
654 |
}
|
jaroslav@1890
|
655 |
|
jaroslav@1890
|
656 |
/**
|
jaroslav@1890
|
657 |
* Reconstitute this lock instance from a stream
|
jaroslav@1890
|
658 |
* @param s the stream
|
jaroslav@1890
|
659 |
*/
|
jaroslav@1890
|
660 |
private void readObject(java.io.ObjectInputStream s)
|
jaroslav@1890
|
661 |
throws java.io.IOException, ClassNotFoundException {
|
jaroslav@1890
|
662 |
s.defaultReadObject();
|
jaroslav@1890
|
663 |
readHolds = new ThreadLocalHoldCounter();
|
jaroslav@1890
|
664 |
setState(0); // reset to unlocked state
|
jaroslav@1890
|
665 |
}
|
jaroslav@1890
|
666 |
|
jaroslav@1890
|
667 |
final int getCount() { return getState(); }
|
jaroslav@1890
|
668 |
}
|
jaroslav@1890
|
669 |
|
jaroslav@1890
|
670 |
/**
|
jaroslav@1890
|
671 |
* Nonfair version of Sync
|
jaroslav@1890
|
672 |
*/
|
jaroslav@1890
|
673 |
static final class NonfairSync extends Sync {
|
jaroslav@1890
|
674 |
private static final long serialVersionUID = -8159625535654395037L;
|
jaroslav@1890
|
675 |
final boolean writerShouldBlock() {
|
jaroslav@1890
|
676 |
return false; // writers can always barge
|
jaroslav@1890
|
677 |
}
|
jaroslav@1890
|
678 |
final boolean readerShouldBlock() {
|
jaroslav@1890
|
679 |
/* As a heuristic to avoid indefinite writer starvation,
|
jaroslav@1890
|
680 |
* block if the thread that momentarily appears to be head
|
jaroslav@1890
|
681 |
* of queue, if one exists, is a waiting writer. This is
|
jaroslav@1890
|
682 |
* only a probabilistic effect since a new reader will not
|
jaroslav@1890
|
683 |
* block if there is a waiting writer behind other enabled
|
jaroslav@1890
|
684 |
* readers that have not yet drained from the queue.
|
jaroslav@1890
|
685 |
*/
|
jaroslav@1890
|
686 |
return apparentlyFirstQueuedIsExclusive();
|
jaroslav@1890
|
687 |
}
|
jaroslav@1890
|
688 |
}
|
jaroslav@1890
|
689 |
|
jaroslav@1890
|
690 |
/**
|
jaroslav@1890
|
691 |
* Fair version of Sync
|
jaroslav@1890
|
692 |
*/
|
jaroslav@1890
|
693 |
static final class FairSync extends Sync {
|
jaroslav@1890
|
694 |
private static final long serialVersionUID = -2274990926593161451L;
|
jaroslav@1890
|
695 |
final boolean writerShouldBlock() {
|
jaroslav@1890
|
696 |
return hasQueuedPredecessors();
|
jaroslav@1890
|
697 |
}
|
jaroslav@1890
|
698 |
final boolean readerShouldBlock() {
|
jaroslav@1890
|
699 |
return hasQueuedPredecessors();
|
jaroslav@1890
|
700 |
}
|
jaroslav@1890
|
701 |
}
|
jaroslav@1890
|
702 |
|
jaroslav@1890
|
703 |
/**
|
jaroslav@1890
|
704 |
* The lock returned by method {@link ReentrantReadWriteLock#readLock}.
|
jaroslav@1890
|
705 |
*/
|
jaroslav@1890
|
706 |
public static class ReadLock implements Lock, java.io.Serializable {
|
jaroslav@1890
|
707 |
private static final long serialVersionUID = -5992448646407690164L;
|
jaroslav@1890
|
708 |
private final Sync sync;
|
jaroslav@1890
|
709 |
|
jaroslav@1890
|
710 |
/**
|
jaroslav@1890
|
711 |
* Constructor for use by subclasses
|
jaroslav@1890
|
712 |
*
|
jaroslav@1890
|
713 |
* @param lock the outer lock object
|
jaroslav@1890
|
714 |
* @throws NullPointerException if the lock is null
|
jaroslav@1890
|
715 |
*/
|
jaroslav@1890
|
716 |
protected ReadLock(ReentrantReadWriteLock lock) {
|
jaroslav@1890
|
717 |
sync = lock.sync;
|
jaroslav@1890
|
718 |
}
|
jaroslav@1890
|
719 |
|
jaroslav@1890
|
720 |
/**
|
jaroslav@1890
|
721 |
* Acquires the read lock.
|
jaroslav@1890
|
722 |
*
|
jaroslav@1890
|
723 |
* <p>Acquires the read lock if the write lock is not held by
|
jaroslav@1890
|
724 |
* another thread and returns immediately.
|
jaroslav@1890
|
725 |
*
|
jaroslav@1890
|
726 |
* <p>If the write lock is held by another thread then
|
jaroslav@1890
|
727 |
* the current thread becomes disabled for thread scheduling
|
jaroslav@1890
|
728 |
* purposes and lies dormant until the read lock has been acquired.
|
jaroslav@1890
|
729 |
*/
|
jaroslav@1890
|
730 |
public void lock() {
|
jaroslav@1890
|
731 |
sync.acquireShared(1);
|
jaroslav@1890
|
732 |
}
|
jaroslav@1890
|
733 |
|
jaroslav@1890
|
734 |
/**
|
jaroslav@1890
|
735 |
* Acquires the read lock unless the current thread is
|
jaroslav@1890
|
736 |
* {@linkplain Thread#interrupt interrupted}.
|
jaroslav@1890
|
737 |
*
|
jaroslav@1890
|
738 |
* <p>Acquires the read lock if the write lock is not held
|
jaroslav@1890
|
739 |
* by another thread and returns immediately.
|
jaroslav@1890
|
740 |
*
|
jaroslav@1890
|
741 |
* <p>If the write lock is held by another thread then the
|
jaroslav@1890
|
742 |
* current thread becomes disabled for thread scheduling
|
jaroslav@1890
|
743 |
* purposes and lies dormant until one of two things happens:
|
jaroslav@1890
|
744 |
*
|
jaroslav@1890
|
745 |
* <ul>
|
jaroslav@1890
|
746 |
*
|
jaroslav@1890
|
747 |
* <li>The read lock is acquired by the current thread; or
|
jaroslav@1890
|
748 |
*
|
jaroslav@1890
|
749 |
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
|
jaroslav@1890
|
750 |
* the current thread.
|
jaroslav@1890
|
751 |
*
|
jaroslav@1890
|
752 |
* </ul>
|
jaroslav@1890
|
753 |
*
|
jaroslav@1890
|
754 |
* <p>If the current thread:
|
jaroslav@1890
|
755 |
*
|
jaroslav@1890
|
756 |
* <ul>
|
jaroslav@1890
|
757 |
*
|
jaroslav@1890
|
758 |
* <li>has its interrupted status set on entry to this method; or
|
jaroslav@1890
|
759 |
*
|
jaroslav@1890
|
760 |
* <li>is {@linkplain Thread#interrupt interrupted} while
|
jaroslav@1890
|
761 |
* acquiring the read lock,
|
jaroslav@1890
|
762 |
*
|
jaroslav@1890
|
763 |
* </ul>
|
jaroslav@1890
|
764 |
*
|
jaroslav@1890
|
765 |
* then {@link InterruptedException} is thrown and the current
|
jaroslav@1890
|
766 |
* thread's interrupted status is cleared.
|
jaroslav@1890
|
767 |
*
|
jaroslav@1890
|
768 |
* <p>In this implementation, as this method is an explicit
|
jaroslav@1890
|
769 |
* interruption point, preference is given to responding to
|
jaroslav@1890
|
770 |
* the interrupt over normal or reentrant acquisition of the
|
jaroslav@1890
|
771 |
* lock.
|
jaroslav@1890
|
772 |
*
|
jaroslav@1890
|
773 |
* @throws InterruptedException if the current thread is interrupted
|
jaroslav@1890
|
774 |
*/
|
jaroslav@1890
|
775 |
public void lockInterruptibly() throws InterruptedException {
|
jaroslav@1890
|
776 |
sync.acquireSharedInterruptibly(1);
|
jaroslav@1890
|
777 |
}
|
jaroslav@1890
|
778 |
|
jaroslav@1890
|
779 |
/**
|
jaroslav@1890
|
780 |
* Acquires the read lock only if the write lock is not held by
|
jaroslav@1890
|
781 |
* another thread at the time of invocation.
|
jaroslav@1890
|
782 |
*
|
jaroslav@1890
|
783 |
* <p>Acquires the read lock if the write lock is not held by
|
jaroslav@1890
|
784 |
* another thread and returns immediately with the value
|
jaroslav@1890
|
785 |
* {@code true}. Even when this lock has been set to use a
|
jaroslav@1890
|
786 |
* fair ordering policy, a call to {@code tryLock()}
|
jaroslav@1890
|
787 |
* <em>will</em> immediately acquire the read lock if it is
|
jaroslav@1890
|
788 |
* available, whether or not other threads are currently
|
jaroslav@1890
|
789 |
* waiting for the read lock. This "barging" behavior
|
jaroslav@1890
|
790 |
* can be useful in certain circumstances, even though it
|
jaroslav@1890
|
791 |
* breaks fairness. If you want to honor the fairness setting
|
jaroslav@1890
|
792 |
* for this lock, then use {@link #tryLock(long, TimeUnit)
|
jaroslav@1890
|
793 |
* tryLock(0, TimeUnit.SECONDS) } which is almost equivalent
|
jaroslav@1890
|
794 |
* (it also detects interruption).
|
jaroslav@1890
|
795 |
*
|
jaroslav@1890
|
796 |
* <p>If the write lock is held by another thread then
|
jaroslav@1890
|
797 |
* this method will return immediately with the value
|
jaroslav@1890
|
798 |
* {@code false}.
|
jaroslav@1890
|
799 |
*
|
jaroslav@1890
|
800 |
* @return {@code true} if the read lock was acquired
|
jaroslav@1890
|
801 |
*/
|
jaroslav@1890
|
802 |
public boolean tryLock() {
|
jaroslav@1890
|
803 |
return sync.tryReadLock();
|
jaroslav@1890
|
804 |
}
|
jaroslav@1890
|
805 |
|
jaroslav@1890
|
806 |
/**
|
jaroslav@1890
|
807 |
* Acquires the read lock if the write lock is not held by
|
jaroslav@1890
|
808 |
* another thread within the given waiting time and the
|
jaroslav@1890
|
809 |
* current thread has not been {@linkplain Thread#interrupt
|
jaroslav@1890
|
810 |
* interrupted}.
|
jaroslav@1890
|
811 |
*
|
jaroslav@1890
|
812 |
* <p>Acquires the read lock if the write lock is not held by
|
jaroslav@1890
|
813 |
* another thread and returns immediately with the value
|
jaroslav@1890
|
814 |
* {@code true}. If this lock has been set to use a fair
|
jaroslav@1890
|
815 |
* ordering policy then an available lock <em>will not</em> be
|
jaroslav@1890
|
816 |
* acquired if any other threads are waiting for the
|
jaroslav@1890
|
817 |
* lock. This is in contrast to the {@link #tryLock()}
|
jaroslav@1890
|
818 |
* method. If you want a timed {@code tryLock} that does
|
jaroslav@1890
|
819 |
* permit barging on a fair lock then combine the timed and
|
jaroslav@1890
|
820 |
* un-timed forms together:
|
jaroslav@1890
|
821 |
*
|
jaroslav@1890
|
822 |
* <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
|
jaroslav@1890
|
823 |
* </pre>
|
jaroslav@1890
|
824 |
*
|
jaroslav@1890
|
825 |
* <p>If the write lock is held by another thread then the
|
jaroslav@1890
|
826 |
* current thread becomes disabled for thread scheduling
|
jaroslav@1890
|
827 |
* purposes and lies dormant until one of three things happens:
|
jaroslav@1890
|
828 |
*
|
jaroslav@1890
|
829 |
* <ul>
|
jaroslav@1890
|
830 |
*
|
jaroslav@1890
|
831 |
* <li>The read lock is acquired by the current thread; or
|
jaroslav@1890
|
832 |
*
|
jaroslav@1890
|
833 |
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
|
jaroslav@1890
|
834 |
* the current thread; or
|
jaroslav@1890
|
835 |
*
|
jaroslav@1890
|
836 |
* <li>The specified waiting time elapses.
|
jaroslav@1890
|
837 |
*
|
jaroslav@1890
|
838 |
* </ul>
|
jaroslav@1890
|
839 |
*
|
jaroslav@1890
|
840 |
* <p>If the read lock is acquired then the value {@code true} is
|
jaroslav@1890
|
841 |
* returned.
|
jaroslav@1890
|
842 |
*
|
jaroslav@1890
|
843 |
* <p>If the current thread:
|
jaroslav@1890
|
844 |
*
|
jaroslav@1890
|
845 |
* <ul>
|
jaroslav@1890
|
846 |
*
|
jaroslav@1890
|
847 |
* <li>has its interrupted status set on entry to this method; or
|
jaroslav@1890
|
848 |
*
|
jaroslav@1890
|
849 |
* <li>is {@linkplain Thread#interrupt interrupted} while
|
jaroslav@1890
|
850 |
* acquiring the read lock,
|
jaroslav@1890
|
851 |
*
|
jaroslav@1890
|
852 |
* </ul> then {@link InterruptedException} is thrown and the
|
jaroslav@1890
|
853 |
* current thread's interrupted status is cleared.
|
jaroslav@1890
|
854 |
*
|
jaroslav@1890
|
855 |
* <p>If the specified waiting time elapses then the value
|
jaroslav@1890
|
856 |
* {@code false} is returned. If the time is less than or
|
jaroslav@1890
|
857 |
* equal to zero, the method will not wait at all.
|
jaroslav@1890
|
858 |
*
|
jaroslav@1890
|
859 |
* <p>In this implementation, as this method is an explicit
|
jaroslav@1890
|
860 |
* interruption point, preference is given to responding to
|
jaroslav@1890
|
861 |
* the interrupt over normal or reentrant acquisition of the
|
jaroslav@1890
|
862 |
* lock, and over reporting the elapse of the waiting time.
|
jaroslav@1890
|
863 |
*
|
jaroslav@1890
|
864 |
* @param timeout the time to wait for the read lock
|
jaroslav@1890
|
865 |
* @param unit the time unit of the timeout argument
|
jaroslav@1890
|
866 |
* @return {@code true} if the read lock was acquired
|
jaroslav@1890
|
867 |
* @throws InterruptedException if the current thread is interrupted
|
jaroslav@1890
|
868 |
* @throws NullPointerException if the time unit is null
|
jaroslav@1890
|
869 |
*
|
jaroslav@1890
|
870 |
*/
|
jaroslav@1890
|
871 |
public boolean tryLock(long timeout, TimeUnit unit)
|
jaroslav@1890
|
872 |
throws InterruptedException {
|
jaroslav@1890
|
873 |
return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
|
jaroslav@1890
|
874 |
}
|
jaroslav@1890
|
875 |
|
jaroslav@1890
|
876 |
/**
|
jaroslav@1890
|
877 |
* Attempts to release this lock.
|
jaroslav@1890
|
878 |
*
|
jaroslav@1890
|
879 |
* <p> If the number of readers is now zero then the lock
|
jaroslav@1890
|
880 |
* is made available for write lock attempts.
|
jaroslav@1890
|
881 |
*/
|
jaroslav@1890
|
882 |
public void unlock() {
|
jaroslav@1890
|
883 |
sync.releaseShared(1);
|
jaroslav@1890
|
884 |
}
|
jaroslav@1890
|
885 |
|
jaroslav@1890
|
886 |
/**
|
jaroslav@1890
|
887 |
* Throws {@code UnsupportedOperationException} because
|
jaroslav@1890
|
888 |
* {@code ReadLocks} do not support conditions.
|
jaroslav@1890
|
889 |
*
|
jaroslav@1890
|
890 |
* @throws UnsupportedOperationException always
|
jaroslav@1890
|
891 |
*/
|
jaroslav@1890
|
892 |
public Condition newCondition() {
|
jaroslav@1890
|
893 |
throw new UnsupportedOperationException();
|
jaroslav@1890
|
894 |
}
|
jaroslav@1890
|
895 |
|
jaroslav@1890
|
896 |
/**
|
jaroslav@1890
|
897 |
* Returns a string identifying this lock, as well as its lock state.
|
jaroslav@1890
|
898 |
* The state, in brackets, includes the String {@code "Read locks ="}
|
jaroslav@1890
|
899 |
* followed by the number of held read locks.
|
jaroslav@1890
|
900 |
*
|
jaroslav@1890
|
901 |
* @return a string identifying this lock, as well as its lock state
|
jaroslav@1890
|
902 |
*/
|
jaroslav@1890
|
903 |
public String toString() {
|
jaroslav@1890
|
904 |
int r = sync.getReadLockCount();
|
jaroslav@1890
|
905 |
return super.toString() +
|
jaroslav@1890
|
906 |
"[Read locks = " + r + "]";
|
jaroslav@1890
|
907 |
}
|
jaroslav@1890
|
908 |
}
|
jaroslav@1890
|
909 |
|
jaroslav@1890
|
910 |
/**
|
jaroslav@1890
|
911 |
* The lock returned by method {@link ReentrantReadWriteLock#writeLock}.
|
jaroslav@1890
|
912 |
*/
|
jaroslav@1890
|
913 |
public static class WriteLock implements Lock, java.io.Serializable {
|
jaroslav@1890
|
914 |
private static final long serialVersionUID = -4992448646407690164L;
|
jaroslav@1890
|
915 |
private final Sync sync;
|
jaroslav@1890
|
916 |
|
jaroslav@1890
|
917 |
/**
|
jaroslav@1890
|
918 |
* Constructor for use by subclasses
|
jaroslav@1890
|
919 |
*
|
jaroslav@1890
|
920 |
* @param lock the outer lock object
|
jaroslav@1890
|
921 |
* @throws NullPointerException if the lock is null
|
jaroslav@1890
|
922 |
*/
|
jaroslav@1890
|
923 |
protected WriteLock(ReentrantReadWriteLock lock) {
|
jaroslav@1890
|
924 |
sync = lock.sync;
|
jaroslav@1890
|
925 |
}
|
jaroslav@1890
|
926 |
|
jaroslav@1890
|
927 |
/**
|
jaroslav@1890
|
928 |
* Acquires the write lock.
|
jaroslav@1890
|
929 |
*
|
jaroslav@1890
|
930 |
* <p>Acquires the write lock if neither the read nor write lock
|
jaroslav@1890
|
931 |
* are held by another thread
|
jaroslav@1890
|
932 |
* and returns immediately, setting the write lock hold count to
|
jaroslav@1890
|
933 |
* one.
|
jaroslav@1890
|
934 |
*
|
jaroslav@1890
|
935 |
* <p>If the current thread already holds the write lock then the
|
jaroslav@1890
|
936 |
* hold count is incremented by one and the method returns
|
jaroslav@1890
|
937 |
* immediately.
|
jaroslav@1890
|
938 |
*
|
jaroslav@1890
|
939 |
* <p>If the lock is held by another thread then the current
|
jaroslav@1890
|
940 |
* thread becomes disabled for thread scheduling purposes and
|
jaroslav@1890
|
941 |
* lies dormant until the write lock has been acquired, at which
|
jaroslav@1890
|
942 |
* time the write lock hold count is set to one.
|
jaroslav@1890
|
943 |
*/
|
jaroslav@1890
|
944 |
public void lock() {
|
jaroslav@1890
|
945 |
sync.acquire(1);
|
jaroslav@1890
|
946 |
}
|
jaroslav@1890
|
947 |
|
jaroslav@1890
|
948 |
/**
|
jaroslav@1890
|
949 |
* Acquires the write lock unless the current thread is
|
jaroslav@1890
|
950 |
* {@linkplain Thread#interrupt interrupted}.
|
jaroslav@1890
|
951 |
*
|
jaroslav@1890
|
952 |
* <p>Acquires the write lock if neither the read nor write lock
|
jaroslav@1890
|
953 |
* are held by another thread
|
jaroslav@1890
|
954 |
* and returns immediately, setting the write lock hold count to
|
jaroslav@1890
|
955 |
* one.
|
jaroslav@1890
|
956 |
*
|
jaroslav@1890
|
957 |
* <p>If the current thread already holds this lock then the
|
jaroslav@1890
|
958 |
* hold count is incremented by one and the method returns
|
jaroslav@1890
|
959 |
* immediately.
|
jaroslav@1890
|
960 |
*
|
jaroslav@1890
|
961 |
* <p>If the lock is held by another thread then the current
|
jaroslav@1890
|
962 |
* thread becomes disabled for thread scheduling purposes and
|
jaroslav@1890
|
963 |
* lies dormant until one of two things happens:
|
jaroslav@1890
|
964 |
*
|
jaroslav@1890
|
965 |
* <ul>
|
jaroslav@1890
|
966 |
*
|
jaroslav@1890
|
967 |
* <li>The write lock is acquired by the current thread; or
|
jaroslav@1890
|
968 |
*
|
jaroslav@1890
|
969 |
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
|
jaroslav@1890
|
970 |
* the current thread.
|
jaroslav@1890
|
971 |
*
|
jaroslav@1890
|
972 |
* </ul>
|
jaroslav@1890
|
973 |
*
|
jaroslav@1890
|
974 |
* <p>If the write lock is acquired by the current thread then the
|
jaroslav@1890
|
975 |
* lock hold count is set to one.
|
jaroslav@1890
|
976 |
*
|
jaroslav@1890
|
977 |
* <p>If the current thread:
|
jaroslav@1890
|
978 |
*
|
jaroslav@1890
|
979 |
* <ul>
|
jaroslav@1890
|
980 |
*
|
jaroslav@1890
|
981 |
* <li>has its interrupted status set on entry to this method;
|
jaroslav@1890
|
982 |
* or
|
jaroslav@1890
|
983 |
*
|
jaroslav@1890
|
984 |
* <li>is {@linkplain Thread#interrupt interrupted} while
|
jaroslav@1890
|
985 |
* acquiring the write lock,
|
jaroslav@1890
|
986 |
*
|
jaroslav@1890
|
987 |
* </ul>
|
jaroslav@1890
|
988 |
*
|
jaroslav@1890
|
989 |
* then {@link InterruptedException} is thrown and the current
|
jaroslav@1890
|
990 |
* thread's interrupted status is cleared.
|
jaroslav@1890
|
991 |
*
|
jaroslav@1890
|
992 |
* <p>In this implementation, as this method is an explicit
|
jaroslav@1890
|
993 |
* interruption point, preference is given to responding to
|
jaroslav@1890
|
994 |
* the interrupt over normal or reentrant acquisition of the
|
jaroslav@1890
|
995 |
* lock.
|
jaroslav@1890
|
996 |
*
|
jaroslav@1890
|
997 |
* @throws InterruptedException if the current thread is interrupted
|
jaroslav@1890
|
998 |
*/
|
jaroslav@1890
|
999 |
public void lockInterruptibly() throws InterruptedException {
|
jaroslav@1890
|
1000 |
sync.acquireInterruptibly(1);
|
jaroslav@1890
|
1001 |
}
|
jaroslav@1890
|
1002 |
|
jaroslav@1890
|
1003 |
/**
|
jaroslav@1890
|
1004 |
* Acquires the write lock only if it is not held by another thread
|
jaroslav@1890
|
1005 |
* at the time of invocation.
|
jaroslav@1890
|
1006 |
*
|
jaroslav@1890
|
1007 |
* <p>Acquires the write lock if neither the read nor write lock
|
jaroslav@1890
|
1008 |
* are held by another thread
|
jaroslav@1890
|
1009 |
* and returns immediately with the value {@code true},
|
jaroslav@1890
|
1010 |
* setting the write lock hold count to one. Even when this lock has
|
jaroslav@1890
|
1011 |
* been set to use a fair ordering policy, a call to
|
jaroslav@1890
|
1012 |
* {@code tryLock()} <em>will</em> immediately acquire the
|
jaroslav@1890
|
1013 |
* lock if it is available, whether or not other threads are
|
jaroslav@1890
|
1014 |
* currently waiting for the write lock. This "barging"
|
jaroslav@1890
|
1015 |
* behavior can be useful in certain circumstances, even
|
jaroslav@1890
|
1016 |
* though it breaks fairness. If you want to honor the
|
jaroslav@1890
|
1017 |
* fairness setting for this lock, then use {@link
|
jaroslav@1890
|
1018 |
* #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
|
jaroslav@1890
|
1019 |
* which is almost equivalent (it also detects interruption).
|
jaroslav@1890
|
1020 |
*
|
jaroslav@1890
|
1021 |
* <p> If the current thread already holds this lock then the
|
jaroslav@1890
|
1022 |
* hold count is incremented by one and the method returns
|
jaroslav@1890
|
1023 |
* {@code true}.
|
jaroslav@1890
|
1024 |
*
|
jaroslav@1890
|
1025 |
* <p>If the lock is held by another thread then this method
|
jaroslav@1890
|
1026 |
* will return immediately with the value {@code false}.
|
jaroslav@1890
|
1027 |
*
|
jaroslav@1890
|
1028 |
* @return {@code true} if the lock was free and was acquired
|
jaroslav@1890
|
1029 |
* by the current thread, or the write lock was already held
|
jaroslav@1890
|
1030 |
* by the current thread; and {@code false} otherwise.
|
jaroslav@1890
|
1031 |
*/
|
jaroslav@1890
|
1032 |
public boolean tryLock( ) {
|
jaroslav@1890
|
1033 |
return sync.tryWriteLock();
|
jaroslav@1890
|
1034 |
}
|
jaroslav@1890
|
1035 |
|
jaroslav@1890
|
1036 |
/**
|
jaroslav@1890
|
1037 |
* Acquires the write lock if it is not held by another thread
|
jaroslav@1890
|
1038 |
* within the given waiting time and the current thread has
|
jaroslav@1890
|
1039 |
* not been {@linkplain Thread#interrupt interrupted}.
|
jaroslav@1890
|
1040 |
*
|
jaroslav@1890
|
1041 |
* <p>Acquires the write lock if neither the read nor write lock
|
jaroslav@1890
|
1042 |
* are held by another thread
|
jaroslav@1890
|
1043 |
* and returns immediately with the value {@code true},
|
jaroslav@1890
|
1044 |
* setting the write lock hold count to one. If this lock has been
|
jaroslav@1890
|
1045 |
* set to use a fair ordering policy then an available lock
|
jaroslav@1890
|
1046 |
* <em>will not</em> be acquired if any other threads are
|
jaroslav@1890
|
1047 |
* waiting for the write lock. This is in contrast to the {@link
|
jaroslav@1890
|
1048 |
* #tryLock()} method. If you want a timed {@code tryLock}
|
jaroslav@1890
|
1049 |
* that does permit barging on a fair lock then combine the
|
jaroslav@1890
|
1050 |
* timed and un-timed forms together:
|
jaroslav@1890
|
1051 |
*
|
jaroslav@1890
|
1052 |
* <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
|
jaroslav@1890
|
1053 |
* </pre>
|
jaroslav@1890
|
1054 |
*
|
jaroslav@1890
|
1055 |
* <p>If the current thread already holds this lock then the
|
jaroslav@1890
|
1056 |
* hold count is incremented by one and the method returns
|
jaroslav@1890
|
1057 |
* {@code true}.
|
jaroslav@1890
|
1058 |
*
|
jaroslav@1890
|
1059 |
* <p>If the lock is held by another thread then the current
|
jaroslav@1890
|
1060 |
* thread becomes disabled for thread scheduling purposes and
|
jaroslav@1890
|
1061 |
* lies dormant until one of three things happens:
|
jaroslav@1890
|
1062 |
*
|
jaroslav@1890
|
1063 |
* <ul>
|
jaroslav@1890
|
1064 |
*
|
jaroslav@1890
|
1065 |
* <li>The write lock is acquired by the current thread; or
|
jaroslav@1890
|
1066 |
*
|
jaroslav@1890
|
1067 |
* <li>Some other thread {@linkplain Thread#interrupt interrupts}
|
jaroslav@1890
|
1068 |
* the current thread; or
|
jaroslav@1890
|
1069 |
*
|
jaroslav@1890
|
1070 |
* <li>The specified waiting time elapses
|
jaroslav@1890
|
1071 |
*
|
jaroslav@1890
|
1072 |
* </ul>
|
jaroslav@1890
|
1073 |
*
|
jaroslav@1890
|
1074 |
* <p>If the write lock is acquired then the value {@code true} is
|
jaroslav@1890
|
1075 |
* returned and the write lock hold count is set to one.
|
jaroslav@1890
|
1076 |
*
|
jaroslav@1890
|
1077 |
* <p>If the current thread:
|
jaroslav@1890
|
1078 |
*
|
jaroslav@1890
|
1079 |
* <ul>
|
jaroslav@1890
|
1080 |
*
|
jaroslav@1890
|
1081 |
* <li>has its interrupted status set on entry to this method;
|
jaroslav@1890
|
1082 |
* or
|
jaroslav@1890
|
1083 |
*
|
jaroslav@1890
|
1084 |
* <li>is {@linkplain Thread#interrupt interrupted} while
|
jaroslav@1890
|
1085 |
* acquiring the write lock,
|
jaroslav@1890
|
1086 |
*
|
jaroslav@1890
|
1087 |
* </ul>
|
jaroslav@1890
|
1088 |
*
|
jaroslav@1890
|
1089 |
* then {@link InterruptedException} is thrown and the current
|
jaroslav@1890
|
1090 |
* thread's interrupted status is cleared.
|
jaroslav@1890
|
1091 |
*
|
jaroslav@1890
|
1092 |
* <p>If the specified waiting time elapses then the value
|
jaroslav@1890
|
1093 |
* {@code false} is returned. If the time is less than or
|
jaroslav@1890
|
1094 |
* equal to zero, the method will not wait at all.
|
jaroslav@1890
|
1095 |
*
|
jaroslav@1890
|
1096 |
* <p>In this implementation, as this method is an explicit
|
jaroslav@1890
|
1097 |
* interruption point, preference is given to responding to
|
jaroslav@1890
|
1098 |
* the interrupt over normal or reentrant acquisition of the
|
jaroslav@1890
|
1099 |
* lock, and over reporting the elapse of the waiting time.
|
jaroslav@1890
|
1100 |
*
|
jaroslav@1890
|
1101 |
* @param timeout the time to wait for the write lock
|
jaroslav@1890
|
1102 |
* @param unit the time unit of the timeout argument
|
jaroslav@1890
|
1103 |
*
|
jaroslav@1890
|
1104 |
* @return {@code true} if the lock was free and was acquired
|
jaroslav@1890
|
1105 |
* by the current thread, or the write lock was already held by the
|
jaroslav@1890
|
1106 |
* current thread; and {@code false} if the waiting time
|
jaroslav@1890
|
1107 |
* elapsed before the lock could be acquired.
|
jaroslav@1890
|
1108 |
*
|
jaroslav@1890
|
1109 |
* @throws InterruptedException if the current thread is interrupted
|
jaroslav@1890
|
1110 |
* @throws NullPointerException if the time unit is null
|
jaroslav@1890
|
1111 |
*
|
jaroslav@1890
|
1112 |
*/
|
jaroslav@1890
|
1113 |
public boolean tryLock(long timeout, TimeUnit unit)
|
jaroslav@1890
|
1114 |
throws InterruptedException {
|
jaroslav@1890
|
1115 |
return sync.tryAcquireNanos(1, unit.toNanos(timeout));
|
jaroslav@1890
|
1116 |
}
|
jaroslav@1890
|
1117 |
|
jaroslav@1890
|
1118 |
/**
|
jaroslav@1890
|
1119 |
* Attempts to release this lock.
|
jaroslav@1890
|
1120 |
*
|
jaroslav@1890
|
1121 |
* <p>If the current thread is the holder of this lock then
|
jaroslav@1890
|
1122 |
* the hold count is decremented. If the hold count is now
|
jaroslav@1890
|
1123 |
* zero then the lock is released. If the current thread is
|
jaroslav@1890
|
1124 |
* not the holder of this lock then {@link
|
jaroslav@1890
|
1125 |
* IllegalMonitorStateException} is thrown.
|
jaroslav@1890
|
1126 |
*
|
jaroslav@1890
|
1127 |
* @throws IllegalMonitorStateException if the current thread does not
|
jaroslav@1890
|
1128 |
* hold this lock.
|
jaroslav@1890
|
1129 |
*/
|
jaroslav@1890
|
1130 |
public void unlock() {
|
jaroslav@1890
|
1131 |
sync.release(1);
|
jaroslav@1890
|
1132 |
}
|
jaroslav@1890
|
1133 |
|
jaroslav@1890
|
1134 |
/**
|
jaroslav@1890
|
1135 |
* Returns a {@link Condition} instance for use with this
|
jaroslav@1890
|
1136 |
* {@link Lock} instance.
|
jaroslav@1890
|
1137 |
* <p>The returned {@link Condition} instance supports the same
|
jaroslav@1890
|
1138 |
* usages as do the {@link Object} monitor methods ({@link
|
jaroslav@1890
|
1139 |
* Object#wait() wait}, {@link Object#notify notify}, and {@link
|
jaroslav@1890
|
1140 |
* Object#notifyAll notifyAll}) when used with the built-in
|
jaroslav@1890
|
1141 |
* monitor lock.
|
jaroslav@1890
|
1142 |
*
|
jaroslav@1890
|
1143 |
* <ul>
|
jaroslav@1890
|
1144 |
*
|
jaroslav@1890
|
1145 |
* <li>If this write lock is not held when any {@link
|
jaroslav@1890
|
1146 |
* Condition} method is called then an {@link
|
jaroslav@1890
|
1147 |
* IllegalMonitorStateException} is thrown. (Read locks are
|
jaroslav@1890
|
1148 |
* held independently of write locks, so are not checked or
|
jaroslav@1890
|
1149 |
* affected. However it is essentially always an error to
|
jaroslav@1890
|
1150 |
* invoke a condition waiting method when the current thread
|
jaroslav@1890
|
1151 |
* has also acquired read locks, since other threads that
|
jaroslav@1890
|
1152 |
* could unblock it will not be able to acquire the write
|
jaroslav@1890
|
1153 |
* lock.)
|
jaroslav@1890
|
1154 |
*
|
jaroslav@1890
|
1155 |
* <li>When the condition {@linkplain Condition#await() waiting}
|
jaroslav@1890
|
1156 |
* methods are called the write lock is released and, before
|
jaroslav@1890
|
1157 |
* they return, the write lock is reacquired and the lock hold
|
jaroslav@1890
|
1158 |
* count restored to what it was when the method was called.
|
jaroslav@1890
|
1159 |
*
|
jaroslav@1890
|
1160 |
* <li>If a thread is {@linkplain Thread#interrupt interrupted} while
|
jaroslav@1890
|
1161 |
* waiting then the wait will terminate, an {@link
|
jaroslav@1890
|
1162 |
* InterruptedException} will be thrown, and the thread's
|
jaroslav@1890
|
1163 |
* interrupted status will be cleared.
|
jaroslav@1890
|
1164 |
*
|
jaroslav@1890
|
1165 |
* <li> Waiting threads are signalled in FIFO order.
|
jaroslav@1890
|
1166 |
*
|
jaroslav@1890
|
1167 |
* <li>The ordering of lock reacquisition for threads returning
|
jaroslav@1890
|
1168 |
* from waiting methods is the same as for threads initially
|
jaroslav@1890
|
1169 |
* acquiring the lock, which is in the default case not specified,
|
jaroslav@1890
|
1170 |
* but for <em>fair</em> locks favors those threads that have been
|
jaroslav@1890
|
1171 |
* waiting the longest.
|
jaroslav@1890
|
1172 |
*
|
jaroslav@1890
|
1173 |
* </ul>
|
jaroslav@1890
|
1174 |
*
|
jaroslav@1890
|
1175 |
* @return the Condition object
|
jaroslav@1890
|
1176 |
*/
|
jaroslav@1890
|
1177 |
public Condition newCondition() {
|
jaroslav@1890
|
1178 |
return sync.newCondition();
|
jaroslav@1890
|
1179 |
}
|
jaroslav@1890
|
1180 |
|
jaroslav@1890
|
1181 |
/**
|
jaroslav@1890
|
1182 |
* Returns a string identifying this lock, as well as its lock
|
jaroslav@1890
|
1183 |
* state. The state, in brackets includes either the String
|
jaroslav@1890
|
1184 |
* {@code "Unlocked"} or the String {@code "Locked by"}
|
jaroslav@1890
|
1185 |
* followed by the {@linkplain Thread#getName name} of the owning thread.
|
jaroslav@1890
|
1186 |
*
|
jaroslav@1890
|
1187 |
* @return a string identifying this lock, as well as its lock state
|
jaroslav@1890
|
1188 |
*/
|
jaroslav@1890
|
1189 |
public String toString() {
|
jaroslav@1890
|
1190 |
Thread o = sync.getOwner();
|
jaroslav@1890
|
1191 |
return super.toString() + ((o == null) ?
|
jaroslav@1890
|
1192 |
"[Unlocked]" :
|
jaroslav@1890
|
1193 |
"[Locked by thread " + o.getName() + "]");
|
jaroslav@1890
|
1194 |
}
|
jaroslav@1890
|
1195 |
|
jaroslav@1890
|
1196 |
/**
|
jaroslav@1890
|
1197 |
* Queries if this write lock is held by the current thread.
|
jaroslav@1890
|
1198 |
* Identical in effect to {@link
|
jaroslav@1890
|
1199 |
* ReentrantReadWriteLock#isWriteLockedByCurrentThread}.
|
jaroslav@1890
|
1200 |
*
|
jaroslav@1890
|
1201 |
* @return {@code true} if the current thread holds this lock and
|
jaroslav@1890
|
1202 |
* {@code false} otherwise
|
jaroslav@1890
|
1203 |
* @since 1.6
|
jaroslav@1890
|
1204 |
*/
|
jaroslav@1890
|
1205 |
public boolean isHeldByCurrentThread() {
|
jaroslav@1890
|
1206 |
return sync.isHeldExclusively();
|
jaroslav@1890
|
1207 |
}
|
jaroslav@1890
|
1208 |
|
jaroslav@1890
|
1209 |
/**
|
jaroslav@1890
|
1210 |
* Queries the number of holds on this write lock by the current
|
jaroslav@1890
|
1211 |
* thread. A thread has a hold on a lock for each lock action
|
jaroslav@1890
|
1212 |
* that is not matched by an unlock action. Identical in effect
|
jaroslav@1890
|
1213 |
* to {@link ReentrantReadWriteLock#getWriteHoldCount}.
|
jaroslav@1890
|
1214 |
*
|
jaroslav@1890
|
1215 |
* @return the number of holds on this lock by the current thread,
|
jaroslav@1890
|
1216 |
* or zero if this lock is not held by the current thread
|
jaroslav@1890
|
1217 |
* @since 1.6
|
jaroslav@1890
|
1218 |
*/
|
jaroslav@1890
|
1219 |
public int getHoldCount() {
|
jaroslav@1890
|
1220 |
return sync.getWriteHoldCount();
|
jaroslav@1890
|
1221 |
}
|
jaroslav@1890
|
1222 |
}
|
jaroslav@1890
|
1223 |
|
jaroslav@1890
|
1224 |
// Instrumentation and status
|
jaroslav@1890
|
1225 |
|
jaroslav@1890
|
1226 |
/**
|
jaroslav@1890
|
1227 |
* Returns {@code true} if this lock has fairness set true.
|
jaroslav@1890
|
1228 |
*
|
jaroslav@1890
|
1229 |
* @return {@code true} if this lock has fairness set true
|
jaroslav@1890
|
1230 |
*/
|
jaroslav@1890
|
1231 |
public final boolean isFair() {
|
jaroslav@1890
|
1232 |
return sync instanceof FairSync;
|
jaroslav@1890
|
1233 |
}
|
jaroslav@1890
|
1234 |
|
jaroslav@1890
|
1235 |
/**
|
jaroslav@1890
|
1236 |
* Returns the thread that currently owns the write lock, or
|
jaroslav@1890
|
1237 |
* {@code null} if not owned. When this method is called by a
|
jaroslav@1890
|
1238 |
* thread that is not the owner, the return value reflects a
|
jaroslav@1890
|
1239 |
* best-effort approximation of current lock status. For example,
|
jaroslav@1890
|
1240 |
* the owner may be momentarily {@code null} even if there are
|
jaroslav@1890
|
1241 |
* threads trying to acquire the lock but have not yet done so.
|
jaroslav@1890
|
1242 |
* This method is designed to facilitate construction of
|
jaroslav@1890
|
1243 |
* subclasses that provide more extensive lock monitoring
|
jaroslav@1890
|
1244 |
* facilities.
|
jaroslav@1890
|
1245 |
*
|
jaroslav@1890
|
1246 |
* @return the owner, or {@code null} if not owned
|
jaroslav@1890
|
1247 |
*/
|
jaroslav@1890
|
1248 |
protected Thread getOwner() {
|
jaroslav@1890
|
1249 |
return sync.getOwner();
|
jaroslav@1890
|
1250 |
}
|
jaroslav@1890
|
1251 |
|
jaroslav@1890
|
1252 |
/**
|
jaroslav@1890
|
1253 |
* Queries the number of read locks held for this lock. This
|
jaroslav@1890
|
1254 |
* method is designed for use in monitoring system state, not for
|
jaroslav@1890
|
1255 |
* synchronization control.
|
jaroslav@1890
|
1256 |
* @return the number of read locks held.
|
jaroslav@1890
|
1257 |
*/
|
jaroslav@1890
|
1258 |
public int getReadLockCount() {
|
jaroslav@1890
|
1259 |
return sync.getReadLockCount();
|
jaroslav@1890
|
1260 |
}
|
jaroslav@1890
|
1261 |
|
jaroslav@1890
|
1262 |
/**
|
jaroslav@1890
|
1263 |
* Queries if the write lock is held by any thread. This method is
|
jaroslav@1890
|
1264 |
* designed for use in monitoring system state, not for
|
jaroslav@1890
|
1265 |
* synchronization control.
|
jaroslav@1890
|
1266 |
*
|
jaroslav@1890
|
1267 |
* @return {@code true} if any thread holds the write lock and
|
jaroslav@1890
|
1268 |
* {@code false} otherwise
|
jaroslav@1890
|
1269 |
*/
|
jaroslav@1890
|
1270 |
public boolean isWriteLocked() {
|
jaroslav@1890
|
1271 |
return sync.isWriteLocked();
|
jaroslav@1890
|
1272 |
}
|
jaroslav@1890
|
1273 |
|
jaroslav@1890
|
1274 |
/**
|
jaroslav@1890
|
1275 |
* Queries if the write lock is held by the current thread.
|
jaroslav@1890
|
1276 |
*
|
jaroslav@1890
|
1277 |
* @return {@code true} if the current thread holds the write lock and
|
jaroslav@1890
|
1278 |
* {@code false} otherwise
|
jaroslav@1890
|
1279 |
*/
|
jaroslav@1890
|
1280 |
public boolean isWriteLockedByCurrentThread() {
|
jaroslav@1890
|
1281 |
return sync.isHeldExclusively();
|
jaroslav@1890
|
1282 |
}
|
jaroslav@1890
|
1283 |
|
jaroslav@1890
|
1284 |
/**
|
jaroslav@1890
|
1285 |
* Queries the number of reentrant write holds on this lock by the
|
jaroslav@1890
|
1286 |
* current thread. A writer thread has a hold on a lock for
|
jaroslav@1890
|
1287 |
* each lock action that is not matched by an unlock action.
|
jaroslav@1890
|
1288 |
*
|
jaroslav@1890
|
1289 |
* @return the number of holds on the write lock by the current thread,
|
jaroslav@1890
|
1290 |
* or zero if the write lock is not held by the current thread
|
jaroslav@1890
|
1291 |
*/
|
jaroslav@1890
|
1292 |
public int getWriteHoldCount() {
|
jaroslav@1890
|
1293 |
return sync.getWriteHoldCount();
|
jaroslav@1890
|
1294 |
}
|
jaroslav@1890
|
1295 |
|
jaroslav@1890
|
1296 |
/**
|
jaroslav@1890
|
1297 |
* Queries the number of reentrant read holds on this lock by the
|
jaroslav@1890
|
1298 |
* current thread. A reader thread has a hold on a lock for
|
jaroslav@1890
|
1299 |
* each lock action that is not matched by an unlock action.
|
jaroslav@1890
|
1300 |
*
|
jaroslav@1890
|
1301 |
* @return the number of holds on the read lock by the current thread,
|
jaroslav@1890
|
1302 |
* or zero if the read lock is not held by the current thread
|
jaroslav@1890
|
1303 |
* @since 1.6
|
jaroslav@1890
|
1304 |
*/
|
jaroslav@1890
|
1305 |
public int getReadHoldCount() {
|
jaroslav@1890
|
1306 |
return sync.getReadHoldCount();
|
jaroslav@1890
|
1307 |
}
|
jaroslav@1890
|
1308 |
|
jaroslav@1890
|
1309 |
/**
|
jaroslav@1890
|
1310 |
* Returns a collection containing threads that may be waiting to
|
jaroslav@1890
|
1311 |
* acquire the write lock. Because the actual set of threads may
|
jaroslav@1890
|
1312 |
* change dynamically while constructing this result, the returned
|
jaroslav@1890
|
1313 |
* collection is only a best-effort estimate. The elements of the
|
jaroslav@1890
|
1314 |
* returned collection are in no particular order. This method is
|
jaroslav@1890
|
1315 |
* designed to facilitate construction of subclasses that provide
|
jaroslav@1890
|
1316 |
* more extensive lock monitoring facilities.
|
jaroslav@1890
|
1317 |
*
|
jaroslav@1890
|
1318 |
* @return the collection of threads
|
jaroslav@1890
|
1319 |
*/
|
jaroslav@1890
|
1320 |
protected Collection<Thread> getQueuedWriterThreads() {
|
jaroslav@1890
|
1321 |
return sync.getExclusiveQueuedThreads();
|
jaroslav@1890
|
1322 |
}
|
jaroslav@1890
|
1323 |
|
jaroslav@1890
|
1324 |
/**
|
jaroslav@1890
|
1325 |
* Returns a collection containing threads that may be waiting to
|
jaroslav@1890
|
1326 |
* acquire the read lock. Because the actual set of threads may
|
jaroslav@1890
|
1327 |
* change dynamically while constructing this result, the returned
|
jaroslav@1890
|
1328 |
* collection is only a best-effort estimate. The elements of the
|
jaroslav@1890
|
1329 |
* returned collection are in no particular order. This method is
|
jaroslav@1890
|
1330 |
* designed to facilitate construction of subclasses that provide
|
jaroslav@1890
|
1331 |
* more extensive lock monitoring facilities.
|
jaroslav@1890
|
1332 |
*
|
jaroslav@1890
|
1333 |
* @return the collection of threads
|
jaroslav@1890
|
1334 |
*/
|
jaroslav@1890
|
1335 |
protected Collection<Thread> getQueuedReaderThreads() {
|
jaroslav@1890
|
1336 |
return sync.getSharedQueuedThreads();
|
jaroslav@1890
|
1337 |
}
|
jaroslav@1890
|
1338 |
|
jaroslav@1890
|
1339 |
/**
|
jaroslav@1890
|
1340 |
* Queries whether any threads are waiting to acquire the read or
|
jaroslav@1890
|
1341 |
* write lock. Note that because cancellations may occur at any
|
jaroslav@1890
|
1342 |
* time, a {@code true} return does not guarantee that any other
|
jaroslav@1890
|
1343 |
* thread will ever acquire a lock. This method is designed
|
jaroslav@1890
|
1344 |
* primarily for use in monitoring of the system state.
|
jaroslav@1890
|
1345 |
*
|
jaroslav@1890
|
1346 |
* @return {@code true} if there may be other threads waiting to
|
jaroslav@1890
|
1347 |
* acquire the lock
|
jaroslav@1890
|
1348 |
*/
|
jaroslav@1890
|
1349 |
public final boolean hasQueuedThreads() {
|
jaroslav@1890
|
1350 |
return sync.hasQueuedThreads();
|
jaroslav@1890
|
1351 |
}
|
jaroslav@1890
|
1352 |
|
jaroslav@1890
|
1353 |
/**
|
jaroslav@1890
|
1354 |
* Queries whether the given thread is waiting to acquire either
|
jaroslav@1890
|
1355 |
* the read or write lock. Note that because cancellations may
|
jaroslav@1890
|
1356 |
* occur at any time, a {@code true} return does not guarantee
|
jaroslav@1890
|
1357 |
* that this thread will ever acquire a lock. This method is
|
jaroslav@1890
|
1358 |
* designed primarily for use in monitoring of the system state.
|
jaroslav@1890
|
1359 |
*
|
jaroslav@1890
|
1360 |
* @param thread the thread
|
jaroslav@1890
|
1361 |
* @return {@code true} if the given thread is queued waiting for this lock
|
jaroslav@1890
|
1362 |
* @throws NullPointerException if the thread is null
|
jaroslav@1890
|
1363 |
*/
|
jaroslav@1890
|
1364 |
public final boolean hasQueuedThread(Thread thread) {
|
jaroslav@1890
|
1365 |
return sync.isQueued(thread);
|
jaroslav@1890
|
1366 |
}
|
jaroslav@1890
|
1367 |
|
jaroslav@1890
|
1368 |
/**
|
jaroslav@1890
|
1369 |
* Returns an estimate of the number of threads waiting to acquire
|
jaroslav@1890
|
1370 |
* either the read or write lock. The value is only an estimate
|
jaroslav@1890
|
1371 |
* because the number of threads may change dynamically while this
|
jaroslav@1890
|
1372 |
* method traverses internal data structures. This method is
|
jaroslav@1890
|
1373 |
* designed for use in monitoring of the system state, not for
|
jaroslav@1890
|
1374 |
* synchronization control.
|
jaroslav@1890
|
1375 |
*
|
jaroslav@1890
|
1376 |
* @return the estimated number of threads waiting for this lock
|
jaroslav@1890
|
1377 |
*/
|
jaroslav@1890
|
1378 |
public final int getQueueLength() {
|
jaroslav@1890
|
1379 |
return sync.getQueueLength();
|
jaroslav@1890
|
1380 |
}
|
jaroslav@1890
|
1381 |
|
jaroslav@1890
|
1382 |
/**
|
jaroslav@1890
|
1383 |
* Returns a collection containing threads that may be waiting to
|
jaroslav@1890
|
1384 |
* acquire either the read or write lock. Because the actual set
|
jaroslav@1890
|
1385 |
* of threads may change dynamically while constructing this
|
jaroslav@1890
|
1386 |
* result, the returned collection is only a best-effort estimate.
|
jaroslav@1890
|
1387 |
* The elements of the returned collection are in no particular
|
jaroslav@1890
|
1388 |
* order. This method is designed to facilitate construction of
|
jaroslav@1890
|
1389 |
* subclasses that provide more extensive monitoring facilities.
|
jaroslav@1890
|
1390 |
*
|
jaroslav@1890
|
1391 |
* @return the collection of threads
|
jaroslav@1890
|
1392 |
*/
|
jaroslav@1890
|
1393 |
protected Collection<Thread> getQueuedThreads() {
|
jaroslav@1890
|
1394 |
return sync.getQueuedThreads();
|
jaroslav@1890
|
1395 |
}
|
jaroslav@1890
|
1396 |
|
jaroslav@1890
|
1397 |
/**
|
jaroslav@1890
|
1398 |
* Queries whether any threads are waiting on the given condition
|
jaroslav@1890
|
1399 |
* associated with the write lock. Note that because timeouts and
|
jaroslav@1890
|
1400 |
* interrupts may occur at any time, a {@code true} return does
|
jaroslav@1890
|
1401 |
* not guarantee that a future {@code signal} will awaken any
|
jaroslav@1890
|
1402 |
* threads. This method is designed primarily for use in
|
jaroslav@1890
|
1403 |
* monitoring of the system state.
|
jaroslav@1890
|
1404 |
*
|
jaroslav@1890
|
1405 |
* @param condition the condition
|
jaroslav@1890
|
1406 |
* @return {@code true} if there are any waiting threads
|
jaroslav@1890
|
1407 |
* @throws IllegalMonitorStateException if this lock is not held
|
jaroslav@1890
|
1408 |
* @throws IllegalArgumentException if the given condition is
|
jaroslav@1890
|
1409 |
* not associated with this lock
|
jaroslav@1890
|
1410 |
* @throws NullPointerException if the condition is null
|
jaroslav@1890
|
1411 |
*/
|
jaroslav@1890
|
1412 |
public boolean hasWaiters(Condition condition) {
|
jaroslav@1890
|
1413 |
if (condition == null)
|
jaroslav@1890
|
1414 |
throw new NullPointerException();
|
jaroslav@1890
|
1415 |
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
|
jaroslav@1890
|
1416 |
throw new IllegalArgumentException("not owner");
|
jaroslav@1890
|
1417 |
return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
|
jaroslav@1890
|
1418 |
}
|
jaroslav@1890
|
1419 |
|
jaroslav@1890
|
1420 |
/**
|
jaroslav@1890
|
1421 |
* Returns an estimate of the number of threads waiting on the
|
jaroslav@1890
|
1422 |
* given condition associated with the write lock. Note that because
|
jaroslav@1890
|
1423 |
* timeouts and interrupts may occur at any time, the estimate
|
jaroslav@1890
|
1424 |
* serves only as an upper bound on the actual number of waiters.
|
jaroslav@1890
|
1425 |
* This method is designed for use in monitoring of the system
|
jaroslav@1890
|
1426 |
* state, not for synchronization control.
|
jaroslav@1890
|
1427 |
*
|
jaroslav@1890
|
1428 |
* @param condition the condition
|
jaroslav@1890
|
1429 |
* @return the estimated number of waiting threads
|
jaroslav@1890
|
1430 |
* @throws IllegalMonitorStateException if this lock is not held
|
jaroslav@1890
|
1431 |
* @throws IllegalArgumentException if the given condition is
|
jaroslav@1890
|
1432 |
* not associated with this lock
|
jaroslav@1890
|
1433 |
* @throws NullPointerException if the condition is null
|
jaroslav@1890
|
1434 |
*/
|
jaroslav@1890
|
1435 |
public int getWaitQueueLength(Condition condition) {
|
jaroslav@1890
|
1436 |
if (condition == null)
|
jaroslav@1890
|
1437 |
throw new NullPointerException();
|
jaroslav@1890
|
1438 |
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
|
jaroslav@1890
|
1439 |
throw new IllegalArgumentException("not owner");
|
jaroslav@1890
|
1440 |
return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
|
jaroslav@1890
|
1441 |
}
|
jaroslav@1890
|
1442 |
|
jaroslav@1890
|
1443 |
/**
|
jaroslav@1890
|
1444 |
* Returns a collection containing those threads that may be
|
jaroslav@1890
|
1445 |
* waiting on the given condition associated with the write lock.
|
jaroslav@1890
|
1446 |
* Because the actual set of threads may change dynamically while
|
jaroslav@1890
|
1447 |
* constructing this result, the returned collection is only a
|
jaroslav@1890
|
1448 |
* best-effort estimate. The elements of the returned collection
|
jaroslav@1890
|
1449 |
* are in no particular order. This method is designed to
|
jaroslav@1890
|
1450 |
* facilitate construction of subclasses that provide more
|
jaroslav@1890
|
1451 |
* extensive condition monitoring facilities.
|
jaroslav@1890
|
1452 |
*
|
jaroslav@1890
|
1453 |
* @param condition the condition
|
jaroslav@1890
|
1454 |
* @return the collection of threads
|
jaroslav@1890
|
1455 |
* @throws IllegalMonitorStateException if this lock is not held
|
jaroslav@1890
|
1456 |
* @throws IllegalArgumentException if the given condition is
|
jaroslav@1890
|
1457 |
* not associated with this lock
|
jaroslav@1890
|
1458 |
* @throws NullPointerException if the condition is null
|
jaroslav@1890
|
1459 |
*/
|
jaroslav@1890
|
1460 |
protected Collection<Thread> getWaitingThreads(Condition condition) {
|
jaroslav@1890
|
1461 |
if (condition == null)
|
jaroslav@1890
|
1462 |
throw new NullPointerException();
|
jaroslav@1890
|
1463 |
if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
|
jaroslav@1890
|
1464 |
throw new IllegalArgumentException("not owner");
|
jaroslav@1890
|
1465 |
return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
|
jaroslav@1890
|
1466 |
}
|
jaroslav@1890
|
1467 |
|
jaroslav@1890
|
1468 |
/**
|
jaroslav@1890
|
1469 |
* Returns a string identifying this lock, as well as its lock state.
|
jaroslav@1890
|
1470 |
* The state, in brackets, includes the String {@code "Write locks ="}
|
jaroslav@1890
|
1471 |
* followed by the number of reentrantly held write locks, and the
|
jaroslav@1890
|
1472 |
* String {@code "Read locks ="} followed by the number of held
|
jaroslav@1890
|
1473 |
* read locks.
|
jaroslav@1890
|
1474 |
*
|
jaroslav@1890
|
1475 |
* @return a string identifying this lock, as well as its lock state
|
jaroslav@1890
|
1476 |
*/
|
jaroslav@1890
|
1477 |
public String toString() {
|
jaroslav@1890
|
1478 |
int c = sync.getCount();
|
jaroslav@1890
|
1479 |
int w = Sync.exclusiveCount(c);
|
jaroslav@1890
|
1480 |
int r = Sync.sharedCount(c);
|
jaroslav@1890
|
1481 |
|
jaroslav@1890
|
1482 |
return super.toString() +
|
jaroslav@1890
|
1483 |
"[Write locks = " + w + ", Read locks = " + r + "]";
|
jaroslav@1890
|
1484 |
}
|
jaroslav@1890
|
1485 |
|
jaroslav@1890
|
1486 |
}
|