jaroslav@1890: /*
jaroslav@1890:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@1890:  *
jaroslav@1890:  * This code is free software; you can redistribute it and/or modify it
jaroslav@1890:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@1890:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@1890:  * particular file as subject to the "Classpath" exception as provided
jaroslav@1890:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@1890:  *
jaroslav@1890:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@1890:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@1890:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@1890:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@1890:  * accompanied this code).
jaroslav@1890:  *
jaroslav@1890:  * You should have received a copy of the GNU General Public License version
jaroslav@1890:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@1890:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@1890:  *
jaroslav@1890:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@1890:  * or visit www.oracle.com if you need additional information or have any
jaroslav@1890:  * questions.
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: /*
jaroslav@1890:  * This file is available under and governed by the GNU General Public
jaroslav@1890:  * License version 2 only, as published by the Free Software Foundation.
jaroslav@1890:  * However, the following notice accompanied the original version of this
jaroslav@1890:  * file:
jaroslav@1890:  *
jaroslav@1890:  * Written by Doug Lea with assistance from members of JCP JSR-166
jaroslav@1890:  * Expert Group and released to the public domain, as explained at
jaroslav@1890:  * http://creativecommons.org/publicdomain/zero/1.0/
jaroslav@1890:  */
jaroslav@1890: 
jaroslav@1890: package java.util.concurrent.locks;
jaroslav@1890: import java.util.concurrent.*;
jaroslav@1890: import java.util.concurrent.atomic.*;
jaroslav@1890: import java.util.*;
jaroslav@1890: 
jaroslav@1890: /**
jaroslav@1890:  * An implementation of {@link ReadWriteLock} supporting similar
jaroslav@1890:  * semantics to {@link ReentrantLock}.
jaroslav@1890:  * <p>This class has the following properties:
jaroslav@1890:  *
jaroslav@1890:  * <ul>
jaroslav@1890:  * <li><b>Acquisition order</b>
jaroslav@1890:  *
jaroslav@1890:  * <p> This class does not impose a reader or writer preference
jaroslav@1890:  * ordering for lock access.  However, it does support an optional
jaroslav@1890:  * <em>fairness</em> policy.
jaroslav@1890:  *
jaroslav@1890:  * <dl>
jaroslav@1890:  * <dt><b><i>Non-fair mode (default)</i></b>
jaroslav@1890:  * <dd>When constructed as non-fair (the default), the order of entry
jaroslav@1890:  * to the read and write lock is unspecified, subject to reentrancy
jaroslav@1890:  * constraints.  A nonfair lock that is continuously contended may
jaroslav@1890:  * indefinitely postpone one or more reader or writer threads, but
jaroslav@1890:  * will normally have higher throughput than a fair lock.
jaroslav@1890:  * <p>
jaroslav@1890:  *
jaroslav@1890:  * <dt><b><i>Fair mode</i></b>
jaroslav@1890:  * <dd> When constructed as fair, threads contend for entry using an
jaroslav@1890:  * approximately arrival-order policy. When the currently held lock
jaroslav@1890:  * is released either the longest-waiting single writer thread will
jaroslav@1890:  * be assigned the write lock, or if there is a group of reader threads
jaroslav@1890:  * waiting longer than all waiting writer threads, that group will be
jaroslav@1890:  * assigned the read lock.
jaroslav@1890:  *
jaroslav@1890:  * <p>A thread that tries to acquire a fair read lock (non-reentrantly)
jaroslav@1890:  * will block if either the write lock is held, or there is a waiting
jaroslav@1890:  * writer thread. The thread will not acquire the read lock until
jaroslav@1890:  * after the oldest currently waiting writer thread has acquired and
jaroslav@1890:  * released the write lock. Of course, if a waiting writer abandons
jaroslav@1890:  * its wait, leaving one or more reader threads as the longest waiters
jaroslav@1890:  * in the queue with the write lock free, then those readers will be
jaroslav@1890:  * assigned the read lock.
jaroslav@1890:  *
jaroslav@1890:  * <p>A thread that tries to acquire a fair write lock (non-reentrantly)
jaroslav@1890:  * will block unless both the read lock and write lock are free (which
jaroslav@1890:  * implies there are no waiting threads).  (Note that the non-blocking
jaroslav@1890:  * {@link ReadLock#tryLock()} and {@link WriteLock#tryLock()} methods
jaroslav@1890:  * do not honor this fair setting and will acquire the lock if it is
jaroslav@1890:  * possible, regardless of waiting threads.)
jaroslav@1890:  * <p>
jaroslav@1890:  * </dl>
jaroslav@1890:  *
jaroslav@1890:  * <li><b>Reentrancy</b>
jaroslav@1890:  *
jaroslav@1890:  * <p>This lock allows both readers and writers to reacquire read or
jaroslav@1890:  * write locks in the style of a {@link ReentrantLock}. Non-reentrant
jaroslav@1890:  * readers are not allowed until all write locks held by the writing
jaroslav@1890:  * thread have been released.
jaroslav@1890:  *
jaroslav@1890:  * <p>Additionally, a writer can acquire the read lock, but not
jaroslav@1890:  * vice-versa.  Among other applications, reentrancy can be useful
jaroslav@1890:  * when write locks are held during calls or callbacks to methods that
jaroslav@1890:  * perform reads under read locks.  If a reader tries to acquire the
jaroslav@1890:  * write lock it will never succeed.
jaroslav@1890:  *
jaroslav@1890:  * <li><b>Lock downgrading</b>
jaroslav@1890:  * <p>Reentrancy also allows downgrading from the write lock to a read lock,
jaroslav@1890:  * by acquiring the write lock, then the read lock and then releasing the
jaroslav@1890:  * write lock. However, upgrading from a read lock to the write lock is
jaroslav@1890:  * <b>not</b> possible.
jaroslav@1890:  *
jaroslav@1890:  * <li><b>Interruption of lock acquisition</b>
jaroslav@1890:  * <p>The read lock and write lock both support interruption during lock
jaroslav@1890:  * acquisition.
jaroslav@1890:  *
jaroslav@1890:  * <li><b>{@link Condition} support</b>
jaroslav@1890:  * <p>The write lock provides a {@link Condition} implementation that
jaroslav@1890:  * behaves in the same way, with respect to the write lock, as the
jaroslav@1890:  * {@link Condition} implementation provided by
jaroslav@1890:  * {@link ReentrantLock#newCondition} does for {@link ReentrantLock}.
jaroslav@1890:  * This {@link Condition} can, of course, only be used with the write lock.
jaroslav@1890:  *
jaroslav@1890:  * <p>The read lock does not support a {@link Condition} and
jaroslav@1890:  * {@code readLock().newCondition()} throws
jaroslav@1890:  * {@code UnsupportedOperationException}.
jaroslav@1890:  *
jaroslav@1890:  * <li><b>Instrumentation</b>
jaroslav@1890:  * <p>This class supports methods to determine whether locks
jaroslav@1890:  * are held or contended. These methods are designed for monitoring
jaroslav@1890:  * system state, not for synchronization control.
jaroslav@1890:  * </ul>
jaroslav@1890:  *
jaroslav@1890:  * <p>Serialization of this class behaves in the same way as built-in
jaroslav@1890:  * locks: a deserialized lock is in the unlocked state, regardless of
jaroslav@1890:  * its state when serialized.
jaroslav@1890:  *
jaroslav@1890:  * <p><b>Sample usages</b>. Here is a code sketch showing how to perform
jaroslav@1890:  * lock downgrading after updating a cache (exception handling is
jaroslav@1890:  * particularly tricky when handling multiple locks in a non-nested
jaroslav@1890:  * fashion):
jaroslav@1890:  *
jaroslav@1890:  * <pre> {@code
jaroslav@1890:  * class CachedData {
jaroslav@1890:  *   Object data;
jaroslav@1890:  *   volatile boolean cacheValid;
jaroslav@1890:  *   final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
jaroslav@1890:  *
jaroslav@1890:  *   void processCachedData() {
jaroslav@1890:  *     rwl.readLock().lock();
jaroslav@1890:  *     if (!cacheValid) {
jaroslav@1890:  *        // Must release read lock before acquiring write lock
jaroslav@1890:  *        rwl.readLock().unlock();
jaroslav@1890:  *        rwl.writeLock().lock();
jaroslav@1890:  *        try {
jaroslav@1890:  *          // Recheck state because another thread might have
jaroslav@1890:  *          // acquired write lock and changed state before we did.
jaroslav@1890:  *          if (!cacheValid) {
jaroslav@1890:  *            data = ...
jaroslav@1890:  *            cacheValid = true;
jaroslav@1890:  *          }
jaroslav@1890:  *          // Downgrade by acquiring read lock before releasing write lock
jaroslav@1890:  *          rwl.readLock().lock();
jaroslav@1890:  *        } finally {
jaroslav@1890:  *          rwl.writeLock().unlock(); // Unlock write, still hold read
jaroslav@1890:  *        }
jaroslav@1890:  *     }
jaroslav@1890:  *
jaroslav@1890:  *     try {
jaroslav@1890:  *       use(data);
jaroslav@1890:  *     } finally {
jaroslav@1890:  *       rwl.readLock().unlock();
jaroslav@1890:  *     }
jaroslav@1890:  *   }
jaroslav@1890:  * }}</pre>
jaroslav@1890:  *
jaroslav@1890:  * ReentrantReadWriteLocks can be used to improve concurrency in some
jaroslav@1890:  * uses of some kinds of Collections. This is typically worthwhile
jaroslav@1890:  * only when the collections are expected to be large, accessed by
jaroslav@1890:  * more reader threads than writer threads, and entail operations with
jaroslav@1890:  * overhead that outweighs synchronization overhead. For example, here
jaroslav@1890:  * is a class using a TreeMap that is expected to be large and
jaroslav@1890:  * concurrently accessed.
jaroslav@1890:  *
jaroslav@1890:  * <pre>{@code
jaroslav@1890:  * class RWDictionary {
jaroslav@1890:  *    private final Map<String, Data> m = new TreeMap<String, Data>();
jaroslav@1890:  *    private final ReentrantReadWriteLock rwl = new ReentrantReadWriteLock();
jaroslav@1890:  *    private final Lock r = rwl.readLock();
jaroslav@1890:  *    private final Lock w = rwl.writeLock();
jaroslav@1890:  *
jaroslav@1890:  *    public Data get(String key) {
jaroslav@1890:  *        r.lock();
jaroslav@1890:  *        try { return m.get(key); }
jaroslav@1890:  *        finally { r.unlock(); }
jaroslav@1890:  *    }
jaroslav@1890:  *    public String[] allKeys() {
jaroslav@1890:  *        r.lock();
jaroslav@1890:  *        try { return m.keySet().toArray(); }
jaroslav@1890:  *        finally { r.unlock(); }
jaroslav@1890:  *    }
jaroslav@1890:  *    public Data put(String key, Data value) {
jaroslav@1890:  *        w.lock();
jaroslav@1890:  *        try { return m.put(key, value); }
jaroslav@1890:  *        finally { w.unlock(); }
jaroslav@1890:  *    }
jaroslav@1890:  *    public void clear() {
jaroslav@1890:  *        w.lock();
jaroslav@1890:  *        try { m.clear(); }
jaroslav@1890:  *        finally { w.unlock(); }
jaroslav@1890:  *    }
jaroslav@1890:  * }}</pre>
jaroslav@1890:  *
jaroslav@1890:  * <h3>Implementation Notes</h3>
jaroslav@1890:  *
jaroslav@1890:  * <p>This lock supports a maximum of 65535 recursive write locks
jaroslav@1890:  * and 65535 read locks. Attempts to exceed these limits result in
jaroslav@1890:  * {@link Error} throws from locking methods.
jaroslav@1890:  *
jaroslav@1890:  * @since 1.5
jaroslav@1890:  * @author Doug Lea
jaroslav@1890:  *
jaroslav@1890:  */
jaroslav@1890: public class ReentrantReadWriteLock
jaroslav@1890:         implements ReadWriteLock, java.io.Serializable {
jaroslav@1890:     private static final long serialVersionUID = -6992448646407690164L;
jaroslav@1890:     /** Inner class providing readlock */
jaroslav@1890:     private final ReentrantReadWriteLock.ReadLock readerLock;
jaroslav@1890:     /** Inner class providing writelock */
jaroslav@1890:     private final ReentrantReadWriteLock.WriteLock writerLock;
jaroslav@1890:     /** Performs all synchronization mechanics */
jaroslav@1890:     final Sync sync;
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a new {@code ReentrantReadWriteLock} with
jaroslav@1890:      * default (nonfair) ordering properties.
jaroslav@1890:      */
jaroslav@1890:     public ReentrantReadWriteLock() {
jaroslav@1890:         this(false);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Creates a new {@code ReentrantReadWriteLock} with
jaroslav@1890:      * the given fairness policy.
jaroslav@1890:      *
jaroslav@1890:      * @param fair {@code true} if this lock should use a fair ordering policy
jaroslav@1890:      */
jaroslav@1890:     public ReentrantReadWriteLock(boolean fair) {
jaroslav@1890:         sync = fair ? new FairSync() : new NonfairSync();
jaroslav@1890:         readerLock = new ReadLock(this);
jaroslav@1890:         writerLock = new WriteLock(this);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     public ReentrantReadWriteLock.WriteLock writeLock() { return writerLock; }
jaroslav@1890:     public ReentrantReadWriteLock.ReadLock  readLock()  { return readerLock; }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Synchronization implementation for ReentrantReadWriteLock.
jaroslav@1890:      * Subclassed into fair and nonfair versions.
jaroslav@1890:      */
jaroslav@1890:     abstract static class Sync extends AbstractQueuedSynchronizer {
jaroslav@1890:         private static final long serialVersionUID = 6317671515068378041L;
jaroslav@1890: 
jaroslav@1890:         /*
jaroslav@1890:          * Read vs write count extraction constants and functions.
jaroslav@1890:          * Lock state is logically divided into two unsigned shorts:
jaroslav@1890:          * The lower one representing the exclusive (writer) lock hold count,
jaroslav@1890:          * and the upper the shared (reader) hold count.
jaroslav@1890:          */
jaroslav@1890: 
jaroslav@1890:         static final int SHARED_SHIFT   = 16;
jaroslav@1890:         static final int SHARED_UNIT    = (1 << SHARED_SHIFT);
jaroslav@1890:         static final int MAX_COUNT      = (1 << SHARED_SHIFT) - 1;
jaroslav@1890:         static final int EXCLUSIVE_MASK = (1 << SHARED_SHIFT) - 1;
jaroslav@1890: 
jaroslav@1890:         /** Returns the number of shared holds represented in count  */
jaroslav@1890:         static int sharedCount(int c)    { return c >>> SHARED_SHIFT; }
jaroslav@1890:         /** Returns the number of exclusive holds represented in count  */
jaroslav@1890:         static int exclusiveCount(int c) { return c & EXCLUSIVE_MASK; }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * A counter for per-thread read hold counts.
jaroslav@1890:          * Maintained as a ThreadLocal; cached in cachedHoldCounter
jaroslav@1890:          */
jaroslav@1890:         static final class HoldCounter {
jaroslav@1890:             int count = 0;
jaroslav@1890:             // Use id, not reference, to avoid garbage retention
jaroslav@1890:             final long tid = Thread.currentThread().getId();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * ThreadLocal subclass. Easiest to explicitly define for sake
jaroslav@1890:          * of deserialization mechanics.
jaroslav@1890:          */
jaroslav@1890:         static final class ThreadLocalHoldCounter
jaroslav@1890:             extends ThreadLocal<HoldCounter> {
jaroslav@1890:             public HoldCounter initialValue() {
jaroslav@1890:                 return new HoldCounter();
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * The number of reentrant read locks held by current thread.
jaroslav@1890:          * Initialized only in constructor and readObject.
jaroslav@1890:          * Removed whenever a thread's read hold count drops to 0.
jaroslav@1890:          */
jaroslav@1890:         private transient ThreadLocalHoldCounter readHolds;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * The hold count of the last thread to successfully acquire
jaroslav@1890:          * readLock. This saves ThreadLocal lookup in the common case
jaroslav@1890:          * where the next thread to release is the last one to
jaroslav@1890:          * acquire. This is non-volatile since it is just used
jaroslav@1890:          * as a heuristic, and would be great for threads to cache.
jaroslav@1890:          *
jaroslav@1890:          * <p>Can outlive the Thread for which it is caching the read
jaroslav@1890:          * hold count, but avoids garbage retention by not retaining a
jaroslav@1890:          * reference to the Thread.
jaroslav@1890:          *
jaroslav@1890:          * <p>Accessed via a benign data race; relies on the memory
jaroslav@1890:          * model's final field and out-of-thin-air guarantees.
jaroslav@1890:          */
jaroslav@1890:         private transient HoldCounter cachedHoldCounter;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * firstReader is the first thread to have acquired the read lock.
jaroslav@1890:          * firstReaderHoldCount is firstReader's hold count.
jaroslav@1890:          *
jaroslav@1890:          * <p>More precisely, firstReader is the unique thread that last
jaroslav@1890:          * changed the shared count from 0 to 1, and has not released the
jaroslav@1890:          * read lock since then; null if there is no such thread.
jaroslav@1890:          *
jaroslav@1890:          * <p>Cannot cause garbage retention unless the thread terminated
jaroslav@1890:          * without relinquishing its read locks, since tryReleaseShared
jaroslav@1890:          * sets it to null.
jaroslav@1890:          *
jaroslav@1890:          * <p>Accessed via a benign data race; relies on the memory
jaroslav@1890:          * model's out-of-thin-air guarantees for references.
jaroslav@1890:          *
jaroslav@1890:          * <p>This allows tracking of read holds for uncontended read
jaroslav@1890:          * locks to be very cheap.
jaroslav@1890:          */
jaroslav@1890:         private transient Thread firstReader = null;
jaroslav@1890:         private transient int firstReaderHoldCount;
jaroslav@1890: 
jaroslav@1890:         Sync() {
jaroslav@1890:             readHolds = new ThreadLocalHoldCounter();
jaroslav@1890:             setState(getState()); // ensures visibility of readHolds
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /*
jaroslav@1890:          * Acquires and releases use the same code for fair and
jaroslav@1890:          * nonfair locks, but differ in whether/how they allow barging
jaroslav@1890:          * when queues are non-empty.
jaroslav@1890:          */
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns true if the current thread, when trying to acquire
jaroslav@1890:          * the read lock, and otherwise eligible to do so, should block
jaroslav@1890:          * because of policy for overtaking other waiting threads.
jaroslav@1890:          */
jaroslav@1890:         abstract boolean readerShouldBlock();
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns true if the current thread, when trying to acquire
jaroslav@1890:          * the write lock, and otherwise eligible to do so, should block
jaroslav@1890:          * because of policy for overtaking other waiting threads.
jaroslav@1890:          */
jaroslav@1890:         abstract boolean writerShouldBlock();
jaroslav@1890: 
jaroslav@1890:         /*
jaroslav@1890:          * Note that tryRelease and tryAcquire can be called by
jaroslav@1890:          * Conditions. So it is possible that their arguments contain
jaroslav@1890:          * both read and write holds that are all released during a
jaroslav@1890:          * condition wait and re-established in tryAcquire.
jaroslav@1890:          */
jaroslav@1890: 
jaroslav@1890:         protected final boolean tryRelease(int releases) {
jaroslav@1890:             if (!isHeldExclusively())
jaroslav@1890:                 throw new IllegalMonitorStateException();
jaroslav@1890:             int nextc = getState() - releases;
jaroslav@1890:             boolean free = exclusiveCount(nextc) == 0;
jaroslav@1890:             if (free)
jaroslav@1890:                 setExclusiveOwnerThread(null);
jaroslav@1890:             setState(nextc);
jaroslav@1890:             return free;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean tryAcquire(int acquires) {
jaroslav@1890:             /*
jaroslav@1890:              * Walkthrough:
jaroslav@1890:              * 1. If read count nonzero or write count nonzero
jaroslav@1890:              *    and owner is a different thread, fail.
jaroslav@1890:              * 2. If count would saturate, fail. (This can only
jaroslav@1890:              *    happen if count is already nonzero.)
jaroslav@1890:              * 3. Otherwise, this thread is eligible for lock if
jaroslav@1890:              *    it is either a reentrant acquire or
jaroslav@1890:              *    queue policy allows it. If so, update state
jaroslav@1890:              *    and set owner.
jaroslav@1890:              */
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             int c = getState();
jaroslav@1890:             int w = exclusiveCount(c);
jaroslav@1890:             if (c != 0) {
jaroslav@1890:                 // (Note: if c != 0 and w == 0 then shared count != 0)
jaroslav@1890:                 if (w == 0 || current != getExclusiveOwnerThread())
jaroslav@1890:                     return false;
jaroslav@1890:                 if (w + exclusiveCount(acquires) > MAX_COUNT)
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:                 // Reentrant acquire
jaroslav@1890:                 setState(c + acquires);
jaroslav@1890:                 return true;
jaroslav@1890:             }
jaroslav@1890:             if (writerShouldBlock() ||
jaroslav@1890:                 !compareAndSetState(c, c + acquires))
jaroslav@1890:                 return false;
jaroslav@1890:             setExclusiveOwnerThread(current);
jaroslav@1890:             return true;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean tryReleaseShared(int unused) {
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             if (firstReader == current) {
jaroslav@1890:                 // assert firstReaderHoldCount > 0;
jaroslav@1890:                 if (firstReaderHoldCount == 1)
jaroslav@1890:                     firstReader = null;
jaroslav@1890:                 else
jaroslav@1890:                     firstReaderHoldCount--;
jaroslav@1890:             } else {
jaroslav@1890:                 HoldCounter rh = cachedHoldCounter;
jaroslav@1890:                 if (rh == null || rh.tid != current.getId())
jaroslav@1890:                     rh = readHolds.get();
jaroslav@1890:                 int count = rh.count;
jaroslav@1890:                 if (count <= 1) {
jaroslav@1890:                     readHolds.remove();
jaroslav@1890:                     if (count <= 0)
jaroslav@1890:                         throw unmatchedUnlockException();
jaroslav@1890:                 }
jaroslav@1890:                 --rh.count;
jaroslav@1890:             }
jaroslav@1890:             for (;;) {
jaroslav@1890:                 int c = getState();
jaroslav@1890:                 int nextc = c - SHARED_UNIT;
jaroslav@1890:                 if (compareAndSetState(c, nextc))
jaroslav@1890:                     // Releasing the read lock has no effect on readers,
jaroslav@1890:                     // but it may allow waiting writers to proceed if
jaroslav@1890:                     // both read and write locks are now free.
jaroslav@1890:                     return nextc == 0;
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         private IllegalMonitorStateException unmatchedUnlockException() {
jaroslav@1890:             return new IllegalMonitorStateException(
jaroslav@1890:                 "attempt to unlock read lock, not locked by current thread");
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final int tryAcquireShared(int unused) {
jaroslav@1890:             /*
jaroslav@1890:              * Walkthrough:
jaroslav@1890:              * 1. If write lock held by another thread, fail.
jaroslav@1890:              * 2. Otherwise, this thread is eligible for
jaroslav@1890:              *    lock wrt state, so ask if it should block
jaroslav@1890:              *    because of queue policy. If not, try
jaroslav@1890:              *    to grant by CASing state and updating count.
jaroslav@1890:              *    Note that step does not check for reentrant
jaroslav@1890:              *    acquires, which is postponed to full version
jaroslav@1890:              *    to avoid having to check hold count in
jaroslav@1890:              *    the more typical non-reentrant case.
jaroslav@1890:              * 3. If step 2 fails either because thread
jaroslav@1890:              *    apparently not eligible or CAS fails or count
jaroslav@1890:              *    saturated, chain to version with full retry loop.
jaroslav@1890:              */
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             int c = getState();
jaroslav@1890:             if (exclusiveCount(c) != 0 &&
jaroslav@1890:                 getExclusiveOwnerThread() != current)
jaroslav@1890:                 return -1;
jaroslav@1890:             int r = sharedCount(c);
jaroslav@1890:             if (!readerShouldBlock() &&
jaroslav@1890:                 r < MAX_COUNT &&
jaroslav@1890:                 compareAndSetState(c, c + SHARED_UNIT)) {
jaroslav@1890:                 if (r == 0) {
jaroslav@1890:                     firstReader = current;
jaroslav@1890:                     firstReaderHoldCount = 1;
jaroslav@1890:                 } else if (firstReader == current) {
jaroslav@1890:                     firstReaderHoldCount++;
jaroslav@1890:                 } else {
jaroslav@1890:                     HoldCounter rh = cachedHoldCounter;
jaroslav@1890:                     if (rh == null || rh.tid != current.getId())
jaroslav@1890:                         cachedHoldCounter = rh = readHolds.get();
jaroslav@1890:                     else if (rh.count == 0)
jaroslav@1890:                         readHolds.set(rh);
jaroslav@1890:                     rh.count++;
jaroslav@1890:                 }
jaroslav@1890:                 return 1;
jaroslav@1890:             }
jaroslav@1890:             return fullTryAcquireShared(current);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Full version of acquire for reads, that handles CAS misses
jaroslav@1890:          * and reentrant reads not dealt with in tryAcquireShared.
jaroslav@1890:          */
jaroslav@1890:         final int fullTryAcquireShared(Thread current) {
jaroslav@1890:             /*
jaroslav@1890:              * This code is in part redundant with that in
jaroslav@1890:              * tryAcquireShared but is simpler overall by not
jaroslav@1890:              * complicating tryAcquireShared with interactions between
jaroslav@1890:              * retries and lazily reading hold counts.
jaroslav@1890:              */
jaroslav@1890:             HoldCounter rh = null;
jaroslav@1890:             for (;;) {
jaroslav@1890:                 int c = getState();
jaroslav@1890:                 if (exclusiveCount(c) != 0) {
jaroslav@1890:                     if (getExclusiveOwnerThread() != current)
jaroslav@1890:                         return -1;
jaroslav@1890:                     // else we hold the exclusive lock; blocking here
jaroslav@1890:                     // would cause deadlock.
jaroslav@1890:                 } else if (readerShouldBlock()) {
jaroslav@1890:                     // Make sure we're not acquiring read lock reentrantly
jaroslav@1890:                     if (firstReader == current) {
jaroslav@1890:                         // assert firstReaderHoldCount > 0;
jaroslav@1890:                     } else {
jaroslav@1890:                         if (rh == null) {
jaroslav@1890:                             rh = cachedHoldCounter;
jaroslav@1890:                             if (rh == null || rh.tid != current.getId()) {
jaroslav@1890:                                 rh = readHolds.get();
jaroslav@1890:                                 if (rh.count == 0)
jaroslav@1890:                                     readHolds.remove();
jaroslav@1890:                             }
jaroslav@1890:                         }
jaroslav@1890:                         if (rh.count == 0)
jaroslav@1890:                             return -1;
jaroslav@1890:                     }
jaroslav@1890:                 }
jaroslav@1890:                 if (sharedCount(c) == MAX_COUNT)
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:                 if (compareAndSetState(c, c + SHARED_UNIT)) {
jaroslav@1890:                     if (sharedCount(c) == 0) {
jaroslav@1890:                         firstReader = current;
jaroslav@1890:                         firstReaderHoldCount = 1;
jaroslav@1890:                     } else if (firstReader == current) {
jaroslav@1890:                         firstReaderHoldCount++;
jaroslav@1890:                     } else {
jaroslav@1890:                         if (rh == null)
jaroslav@1890:                             rh = cachedHoldCounter;
jaroslav@1890:                         if (rh == null || rh.tid != current.getId())
jaroslav@1890:                             rh = readHolds.get();
jaroslav@1890:                         else if (rh.count == 0)
jaroslav@1890:                             readHolds.set(rh);
jaroslav@1890:                         rh.count++;
jaroslav@1890:                         cachedHoldCounter = rh; // cache for release
jaroslav@1890:                     }
jaroslav@1890:                     return 1;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Performs tryLock for write, enabling barging in both modes.
jaroslav@1890:          * This is identical in effect to tryAcquire except for lack
jaroslav@1890:          * of calls to writerShouldBlock.
jaroslav@1890:          */
jaroslav@1890:         final boolean tryWriteLock() {
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             int c = getState();
jaroslav@1890:             if (c != 0) {
jaroslav@1890:                 int w = exclusiveCount(c);
jaroslav@1890:                 if (w == 0 || current != getExclusiveOwnerThread())
jaroslav@1890:                     return false;
jaroslav@1890:                 if (w == MAX_COUNT)
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:             }
jaroslav@1890:             if (!compareAndSetState(c, c + 1))
jaroslav@1890:                 return false;
jaroslav@1890:             setExclusiveOwnerThread(current);
jaroslav@1890:             return true;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Performs tryLock for read, enabling barging in both modes.
jaroslav@1890:          * This is identical in effect to tryAcquireShared except for
jaroslav@1890:          * lack of calls to readerShouldBlock.
jaroslav@1890:          */
jaroslav@1890:         final boolean tryReadLock() {
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             for (;;) {
jaroslav@1890:                 int c = getState();
jaroslav@1890:                 if (exclusiveCount(c) != 0 &&
jaroslav@1890:                     getExclusiveOwnerThread() != current)
jaroslav@1890:                     return false;
jaroslav@1890:                 int r = sharedCount(c);
jaroslav@1890:                 if (r == MAX_COUNT)
jaroslav@1890:                     throw new Error("Maximum lock count exceeded");
jaroslav@1890:                 if (compareAndSetState(c, c + SHARED_UNIT)) {
jaroslav@1890:                     if (r == 0) {
jaroslav@1890:                         firstReader = current;
jaroslav@1890:                         firstReaderHoldCount = 1;
jaroslav@1890:                     } else if (firstReader == current) {
jaroslav@1890:                         firstReaderHoldCount++;
jaroslav@1890:                     } else {
jaroslav@1890:                         HoldCounter rh = cachedHoldCounter;
jaroslav@1890:                         if (rh == null || rh.tid != current.getId())
jaroslav@1890:                             cachedHoldCounter = rh = readHolds.get();
jaroslav@1890:                         else if (rh.count == 0)
jaroslav@1890:                             readHolds.set(rh);
jaroslav@1890:                         rh.count++;
jaroslav@1890:                     }
jaroslav@1890:                     return true;
jaroslav@1890:                 }
jaroslav@1890:             }
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         protected final boolean isHeldExclusively() {
jaroslav@1890:             // While we must in general read state before owner,
jaroslav@1890:             // we don't need to do so to check if current thread is owner
jaroslav@1890:             return getExclusiveOwnerThread() == Thread.currentThread();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         // Methods relayed to outer class
jaroslav@1890: 
jaroslav@1890:         final ConditionObject newCondition() {
jaroslav@1890:             return new ConditionObject();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final Thread getOwner() {
jaroslav@1890:             // Must read state before owner to ensure memory consistency
jaroslav@1890:             return ((exclusiveCount(getState()) == 0) ?
jaroslav@1890:                     null :
jaroslav@1890:                     getExclusiveOwnerThread());
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final int getReadLockCount() {
jaroslav@1890:             return sharedCount(getState());
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final boolean isWriteLocked() {
jaroslav@1890:             return exclusiveCount(getState()) != 0;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final int getWriteHoldCount() {
jaroslav@1890:             return isHeldExclusively() ? exclusiveCount(getState()) : 0;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final int getReadHoldCount() {
jaroslav@1890:             if (getReadLockCount() == 0)
jaroslav@1890:                 return 0;
jaroslav@1890: 
jaroslav@1890:             Thread current = Thread.currentThread();
jaroslav@1890:             if (firstReader == current)
jaroslav@1890:                 return firstReaderHoldCount;
jaroslav@1890: 
jaroslav@1890:             HoldCounter rh = cachedHoldCounter;
jaroslav@1890:             if (rh != null && rh.tid == current.getId())
jaroslav@1890:                 return rh.count;
jaroslav@1890: 
jaroslav@1890:             int count = readHolds.get().count;
jaroslav@1890:             if (count == 0) readHolds.remove();
jaroslav@1890:             return count;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Reconstitute this lock instance from a stream
jaroslav@1890:          * @param s the stream
jaroslav@1890:          */
jaroslav@1890:         private void readObject(java.io.ObjectInputStream s)
jaroslav@1890:             throws java.io.IOException, ClassNotFoundException {
jaroslav@1890:             s.defaultReadObject();
jaroslav@1890:             readHolds = new ThreadLocalHoldCounter();
jaroslav@1890:             setState(0); // reset to unlocked state
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         final int getCount() { return getState(); }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Nonfair version of Sync
jaroslav@1890:      */
jaroslav@1890:     static final class NonfairSync extends Sync {
jaroslav@1890:         private static final long serialVersionUID = -8159625535654395037L;
jaroslav@1890:         final boolean writerShouldBlock() {
jaroslav@1890:             return false; // writers can always barge
jaroslav@1890:         }
jaroslav@1890:         final boolean readerShouldBlock() {
jaroslav@1890:             /* As a heuristic to avoid indefinite writer starvation,
jaroslav@1890:              * block if the thread that momentarily appears to be head
jaroslav@1890:              * of queue, if one exists, is a waiting writer.  This is
jaroslav@1890:              * only a probabilistic effect since a new reader will not
jaroslav@1890:              * block if there is a waiting writer behind other enabled
jaroslav@1890:              * readers that have not yet drained from the queue.
jaroslav@1890:              */
jaroslav@1890:             return apparentlyFirstQueuedIsExclusive();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Fair version of Sync
jaroslav@1890:      */
jaroslav@1890:     static final class FairSync extends Sync {
jaroslav@1890:         private static final long serialVersionUID = -2274990926593161451L;
jaroslav@1890:         final boolean writerShouldBlock() {
jaroslav@1890:             return hasQueuedPredecessors();
jaroslav@1890:         }
jaroslav@1890:         final boolean readerShouldBlock() {
jaroslav@1890:             return hasQueuedPredecessors();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The lock returned by method {@link ReentrantReadWriteLock#readLock}.
jaroslav@1890:      */
jaroslav@1890:     public static class ReadLock implements Lock, java.io.Serializable {
jaroslav@1890:         private static final long serialVersionUID = -5992448646407690164L;
jaroslav@1890:         private final Sync sync;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Constructor for use by subclasses
jaroslav@1890:          *
jaroslav@1890:          * @param lock the outer lock object
jaroslav@1890:          * @throws NullPointerException if the lock is null
jaroslav@1890:          */
jaroslav@1890:         protected ReadLock(ReentrantReadWriteLock lock) {
jaroslav@1890:             sync = lock.sync;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the read lock.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the read lock if the write lock is not held by
jaroslav@1890:          * another thread and returns immediately.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is held by another thread then
jaroslav@1890:          * the current thread becomes disabled for thread scheduling
jaroslav@1890:          * purposes and lies dormant until the read lock has been acquired.
jaroslav@1890:          */
jaroslav@1890:         public void lock() {
jaroslav@1890:             sync.acquireShared(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the read lock unless the current thread is
jaroslav@1890:          * {@linkplain Thread#interrupt interrupted}.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the read lock if the write lock is not held
jaroslav@1890:          * by another thread and returns immediately.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is held by another thread then the
jaroslav@1890:          * current thread becomes disabled for thread scheduling
jaroslav@1890:          * purposes and lies dormant until one of two things happens:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>The read lock is acquired by the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>Some other thread {@linkplain Thread#interrupt interrupts}
jaroslav@1890:          * the current thread.
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>has its interrupted status set on entry to this method; or
jaroslav@1890:          *
jaroslav@1890:          * <li>is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:          * acquiring the read lock,
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * then {@link InterruptedException} is thrown and the current
jaroslav@1890:          * thread's interrupted status is cleared.
jaroslav@1890:          *
jaroslav@1890:          * <p>In this implementation, as this method is an explicit
jaroslav@1890:          * interruption point, preference is given to responding to
jaroslav@1890:          * the interrupt over normal or reentrant acquisition of the
jaroslav@1890:          * lock.
jaroslav@1890:          *
jaroslav@1890:          * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:          */
jaroslav@1890:         public void lockInterruptibly() throws InterruptedException {
jaroslav@1890:             sync.acquireSharedInterruptibly(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the read lock only if the write lock is not held by
jaroslav@1890:          * another thread at the time of invocation.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the read lock if the write lock is not held by
jaroslav@1890:          * another thread and returns immediately with the value
jaroslav@1890:          * {@code true}. Even when this lock has been set to use a
jaroslav@1890:          * fair ordering policy, a call to {@code tryLock()}
jaroslav@1890:          * <em>will</em> immediately acquire the read lock if it is
jaroslav@1890:          * available, whether or not other threads are currently
jaroslav@1890:          * waiting for the read lock.  This &quot;barging&quot; behavior
jaroslav@1890:          * can be useful in certain circumstances, even though it
jaroslav@1890:          * breaks fairness. If you want to honor the fairness setting
jaroslav@1890:          * for this lock, then use {@link #tryLock(long, TimeUnit)
jaroslav@1890:          * tryLock(0, TimeUnit.SECONDS) } which is almost equivalent
jaroslav@1890:          * (it also detects interruption).
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is held by another thread then
jaroslav@1890:          * this method will return immediately with the value
jaroslav@1890:          * {@code false}.
jaroslav@1890:          *
jaroslav@1890:          * @return {@code true} if the read lock was acquired
jaroslav@1890:          */
jaroslav@1890:         public  boolean tryLock() {
jaroslav@1890:             return sync.tryReadLock();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the read lock if the write lock is not held by
jaroslav@1890:          * another thread within the given waiting time and the
jaroslav@1890:          * current thread has not been {@linkplain Thread#interrupt
jaroslav@1890:          * interrupted}.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the read lock if the write lock is not held by
jaroslav@1890:          * another thread and returns immediately with the value
jaroslav@1890:          * {@code true}. If this lock has been set to use a fair
jaroslav@1890:          * ordering policy then an available lock <em>will not</em> be
jaroslav@1890:          * acquired if any other threads are waiting for the
jaroslav@1890:          * lock. This is in contrast to the {@link #tryLock()}
jaroslav@1890:          * method. If you want a timed {@code tryLock} that does
jaroslav@1890:          * permit barging on a fair lock then combine the timed and
jaroslav@1890:          * un-timed forms together:
jaroslav@1890:          *
jaroslav@1890:          * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
jaroslav@1890:          * </pre>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is held by another thread then the
jaroslav@1890:          * current thread becomes disabled for thread scheduling
jaroslav@1890:          * purposes and lies dormant until one of three things happens:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>The read lock is acquired by the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>Some other thread {@linkplain Thread#interrupt interrupts}
jaroslav@1890:          * the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>The specified waiting time elapses.
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the read lock is acquired then the value {@code true} is
jaroslav@1890:          * returned.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>has its interrupted status set on entry to this method; or
jaroslav@1890:          *
jaroslav@1890:          * <li>is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:          * acquiring the read lock,
jaroslav@1890:          *
jaroslav@1890:          * </ul> then {@link InterruptedException} is thrown and the
jaroslav@1890:          * current thread's interrupted status is cleared.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the specified waiting time elapses then the value
jaroslav@1890:          * {@code false} is returned.  If the time is less than or
jaroslav@1890:          * equal to zero, the method will not wait at all.
jaroslav@1890:          *
jaroslav@1890:          * <p>In this implementation, as this method is an explicit
jaroslav@1890:          * interruption point, preference is given to responding to
jaroslav@1890:          * the interrupt over normal or reentrant acquisition of the
jaroslav@1890:          * lock, and over reporting the elapse of the waiting time.
jaroslav@1890:          *
jaroslav@1890:          * @param timeout the time to wait for the read lock
jaroslav@1890:          * @param unit the time unit of the timeout argument
jaroslav@1890:          * @return {@code true} if the read lock was acquired
jaroslav@1890:          * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:          * @throws NullPointerException if the time unit is null
jaroslav@1890:          *
jaroslav@1890:          */
jaroslav@1890:         public boolean tryLock(long timeout, TimeUnit unit)
jaroslav@1890:                 throws InterruptedException {
jaroslav@1890:             return sync.tryAcquireSharedNanos(1, unit.toNanos(timeout));
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Attempts to release this lock.
jaroslav@1890:          *
jaroslav@1890:          * <p> If the number of readers is now zero then the lock
jaroslav@1890:          * is made available for write lock attempts.
jaroslav@1890:          */
jaroslav@1890:         public  void unlock() {
jaroslav@1890:             sync.releaseShared(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Throws {@code UnsupportedOperationException} because
jaroslav@1890:          * {@code ReadLocks} do not support conditions.
jaroslav@1890:          *
jaroslav@1890:          * @throws UnsupportedOperationException always
jaroslav@1890:          */
jaroslav@1890:         public Condition newCondition() {
jaroslav@1890:             throw new UnsupportedOperationException();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns a string identifying this lock, as well as its lock state.
jaroslav@1890:          * The state, in brackets, includes the String {@code "Read locks ="}
jaroslav@1890:          * followed by the number of held read locks.
jaroslav@1890:          *
jaroslav@1890:          * @return a string identifying this lock, as well as its lock state
jaroslav@1890:          */
jaroslav@1890:         public String toString() {
jaroslav@1890:             int r = sync.getReadLockCount();
jaroslav@1890:             return super.toString() +
jaroslav@1890:                 "[Read locks = " + r + "]";
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * The lock returned by method {@link ReentrantReadWriteLock#writeLock}.
jaroslav@1890:      */
jaroslav@1890:     public static class WriteLock implements Lock, java.io.Serializable {
jaroslav@1890:         private static final long serialVersionUID = -4992448646407690164L;
jaroslav@1890:         private final Sync sync;
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Constructor for use by subclasses
jaroslav@1890:          *
jaroslav@1890:          * @param lock the outer lock object
jaroslav@1890:          * @throws NullPointerException if the lock is null
jaroslav@1890:          */
jaroslav@1890:         protected WriteLock(ReentrantReadWriteLock lock) {
jaroslav@1890:             sync = lock.sync;
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the write lock.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the write lock if neither the read nor write lock
jaroslav@1890:          * are held by another thread
jaroslav@1890:          * and returns immediately, setting the write lock hold count to
jaroslav@1890:          * one.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread already holds the write lock then the
jaroslav@1890:          * hold count is incremented by one and the method returns
jaroslav@1890:          * immediately.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the lock is held by another thread then the current
jaroslav@1890:          * thread becomes disabled for thread scheduling purposes and
jaroslav@1890:          * lies dormant until the write lock has been acquired, at which
jaroslav@1890:          * time the write lock hold count is set to one.
jaroslav@1890:          */
jaroslav@1890:         public void lock() {
jaroslav@1890:             sync.acquire(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the write lock unless the current thread is
jaroslav@1890:          * {@linkplain Thread#interrupt interrupted}.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the write lock if neither the read nor write lock
jaroslav@1890:          * are held by another thread
jaroslav@1890:          * and returns immediately, setting the write lock hold count to
jaroslav@1890:          * one.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread already holds this lock then the
jaroslav@1890:          * hold count is incremented by one and the method returns
jaroslav@1890:          * immediately.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the lock is held by another thread then the current
jaroslav@1890:          * thread becomes disabled for thread scheduling purposes and
jaroslav@1890:          * lies dormant until one of two things happens:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>The write lock is acquired by the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>Some other thread {@linkplain Thread#interrupt interrupts}
jaroslav@1890:          * the current thread.
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is acquired by the current thread then the
jaroslav@1890:          * lock hold count is set to one.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>has its interrupted status set on entry to this method;
jaroslav@1890:          * or
jaroslav@1890:          *
jaroslav@1890:          * <li>is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:          * acquiring the write lock,
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * then {@link InterruptedException} is thrown and the current
jaroslav@1890:          * thread's interrupted status is cleared.
jaroslav@1890:          *
jaroslav@1890:          * <p>In this implementation, as this method is an explicit
jaroslav@1890:          * interruption point, preference is given to responding to
jaroslav@1890:          * the interrupt over normal or reentrant acquisition of the
jaroslav@1890:          * lock.
jaroslav@1890:          *
jaroslav@1890:          * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:          */
jaroslav@1890:         public void lockInterruptibly() throws InterruptedException {
jaroslav@1890:             sync.acquireInterruptibly(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the write lock only if it is not held by another thread
jaroslav@1890:          * at the time of invocation.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the write lock if neither the read nor write lock
jaroslav@1890:          * are held by another thread
jaroslav@1890:          * and returns immediately with the value {@code true},
jaroslav@1890:          * setting the write lock hold count to one. Even when this lock has
jaroslav@1890:          * been set to use a fair ordering policy, a call to
jaroslav@1890:          * {@code tryLock()} <em>will</em> immediately acquire the
jaroslav@1890:          * lock if it is available, whether or not other threads are
jaroslav@1890:          * currently waiting for the write lock.  This &quot;barging&quot;
jaroslav@1890:          * behavior can be useful in certain circumstances, even
jaroslav@1890:          * though it breaks fairness. If you want to honor the
jaroslav@1890:          * fairness setting for this lock, then use {@link
jaroslav@1890:          * #tryLock(long, TimeUnit) tryLock(0, TimeUnit.SECONDS) }
jaroslav@1890:          * which is almost equivalent (it also detects interruption).
jaroslav@1890:          *
jaroslav@1890:          * <p> If the current thread already holds this lock then the
jaroslav@1890:          * hold count is incremented by one and the method returns
jaroslav@1890:          * {@code true}.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the lock is held by another thread then this method
jaroslav@1890:          * will return immediately with the value {@code false}.
jaroslav@1890:          *
jaroslav@1890:          * @return {@code true} if the lock was free and was acquired
jaroslav@1890:          * by the current thread, or the write lock was already held
jaroslav@1890:          * by the current thread; and {@code false} otherwise.
jaroslav@1890:          */
jaroslav@1890:         public boolean tryLock( ) {
jaroslav@1890:             return sync.tryWriteLock();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Acquires the write lock if it is not held by another thread
jaroslav@1890:          * within the given waiting time and the current thread has
jaroslav@1890:          * not been {@linkplain Thread#interrupt interrupted}.
jaroslav@1890:          *
jaroslav@1890:          * <p>Acquires the write lock if neither the read nor write lock
jaroslav@1890:          * are held by another thread
jaroslav@1890:          * and returns immediately with the value {@code true},
jaroslav@1890:          * setting the write lock hold count to one. If this lock has been
jaroslav@1890:          * set to use a fair ordering policy then an available lock
jaroslav@1890:          * <em>will not</em> be acquired if any other threads are
jaroslav@1890:          * waiting for the write lock. This is in contrast to the {@link
jaroslav@1890:          * #tryLock()} method. If you want a timed {@code tryLock}
jaroslav@1890:          * that does permit barging on a fair lock then combine the
jaroslav@1890:          * timed and un-timed forms together:
jaroslav@1890:          *
jaroslav@1890:          * <pre>if (lock.tryLock() || lock.tryLock(timeout, unit) ) { ... }
jaroslav@1890:          * </pre>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread already holds this lock then the
jaroslav@1890:          * hold count is incremented by one and the method returns
jaroslav@1890:          * {@code true}.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the lock is held by another thread then the current
jaroslav@1890:          * thread becomes disabled for thread scheduling purposes and
jaroslav@1890:          * lies dormant until one of three things happens:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>The write lock is acquired by the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>Some other thread {@linkplain Thread#interrupt interrupts}
jaroslav@1890:          * the current thread; or
jaroslav@1890:          *
jaroslav@1890:          * <li>The specified waiting time elapses
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * <p>If the write lock is acquired then the value {@code true} is
jaroslav@1890:          * returned and the write lock hold count is set to one.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread:
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>has its interrupted status set on entry to this method;
jaroslav@1890:          * or
jaroslav@1890:          *
jaroslav@1890:          * <li>is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:          * acquiring the write lock,
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * then {@link InterruptedException} is thrown and the current
jaroslav@1890:          * thread's interrupted status is cleared.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the specified waiting time elapses then the value
jaroslav@1890:          * {@code false} is returned.  If the time is less than or
jaroslav@1890:          * equal to zero, the method will not wait at all.
jaroslav@1890:          *
jaroslav@1890:          * <p>In this implementation, as this method is an explicit
jaroslav@1890:          * interruption point, preference is given to responding to
jaroslav@1890:          * the interrupt over normal or reentrant acquisition of the
jaroslav@1890:          * lock, and over reporting the elapse of the waiting time.
jaroslav@1890:          *
jaroslav@1890:          * @param timeout the time to wait for the write lock
jaroslav@1890:          * @param unit the time unit of the timeout argument
jaroslav@1890:          *
jaroslav@1890:          * @return {@code true} if the lock was free and was acquired
jaroslav@1890:          * by the current thread, or the write lock was already held by the
jaroslav@1890:          * current thread; and {@code false} if the waiting time
jaroslav@1890:          * elapsed before the lock could be acquired.
jaroslav@1890:          *
jaroslav@1890:          * @throws InterruptedException if the current thread is interrupted
jaroslav@1890:          * @throws NullPointerException if the time unit is null
jaroslav@1890:          *
jaroslav@1890:          */
jaroslav@1890:         public boolean tryLock(long timeout, TimeUnit unit)
jaroslav@1890:                 throws InterruptedException {
jaroslav@1890:             return sync.tryAcquireNanos(1, unit.toNanos(timeout));
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Attempts to release this lock.
jaroslav@1890:          *
jaroslav@1890:          * <p>If the current thread is the holder of this lock then
jaroslav@1890:          * the hold count is decremented. If the hold count is now
jaroslav@1890:          * zero then the lock is released.  If the current thread is
jaroslav@1890:          * not the holder of this lock then {@link
jaroslav@1890:          * IllegalMonitorStateException} is thrown.
jaroslav@1890:          *
jaroslav@1890:          * @throws IllegalMonitorStateException if the current thread does not
jaroslav@1890:          * hold this lock.
jaroslav@1890:          */
jaroslav@1890:         public void unlock() {
jaroslav@1890:             sync.release(1);
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns a {@link Condition} instance for use with this
jaroslav@1890:          * {@link Lock} instance.
jaroslav@1890:          * <p>The returned {@link Condition} instance supports the same
jaroslav@1890:          * usages as do the {@link Object} monitor methods ({@link
jaroslav@1890:          * Object#wait() wait}, {@link Object#notify notify}, and {@link
jaroslav@1890:          * Object#notifyAll notifyAll}) when used with the built-in
jaroslav@1890:          * monitor lock.
jaroslav@1890:          *
jaroslav@1890:          * <ul>
jaroslav@1890:          *
jaroslav@1890:          * <li>If this write lock is not held when any {@link
jaroslav@1890:          * Condition} method is called then an {@link
jaroslav@1890:          * IllegalMonitorStateException} is thrown.  (Read locks are
jaroslav@1890:          * held independently of write locks, so are not checked or
jaroslav@1890:          * affected. However it is essentially always an error to
jaroslav@1890:          * invoke a condition waiting method when the current thread
jaroslav@1890:          * has also acquired read locks, since other threads that
jaroslav@1890:          * could unblock it will not be able to acquire the write
jaroslav@1890:          * lock.)
jaroslav@1890:          *
jaroslav@1890:          * <li>When the condition {@linkplain Condition#await() waiting}
jaroslav@1890:          * methods are called the write lock is released and, before
jaroslav@1890:          * they return, the write lock is reacquired and the lock hold
jaroslav@1890:          * count restored to what it was when the method was called.
jaroslav@1890:          *
jaroslav@1890:          * <li>If a thread is {@linkplain Thread#interrupt interrupted} while
jaroslav@1890:          * waiting then the wait will terminate, an {@link
jaroslav@1890:          * InterruptedException} will be thrown, and the thread's
jaroslav@1890:          * interrupted status will be cleared.
jaroslav@1890:          *
jaroslav@1890:          * <li> Waiting threads are signalled in FIFO order.
jaroslav@1890:          *
jaroslav@1890:          * <li>The ordering of lock reacquisition for threads returning
jaroslav@1890:          * from waiting methods is the same as for threads initially
jaroslav@1890:          * acquiring the lock, which is in the default case not specified,
jaroslav@1890:          * but for <em>fair</em> locks favors those threads that have been
jaroslav@1890:          * waiting the longest.
jaroslav@1890:          *
jaroslav@1890:          * </ul>
jaroslav@1890:          *
jaroslav@1890:          * @return the Condition object
jaroslav@1890:          */
jaroslav@1890:         public Condition newCondition() {
jaroslav@1890:             return sync.newCondition();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Returns a string identifying this lock, as well as its lock
jaroslav@1890:          * state.  The state, in brackets includes either the String
jaroslav@1890:          * {@code "Unlocked"} or the String {@code "Locked by"}
jaroslav@1890:          * followed by the {@linkplain Thread#getName name} of the owning thread.
jaroslav@1890:          *
jaroslav@1890:          * @return a string identifying this lock, as well as its lock state
jaroslav@1890:          */
jaroslav@1890:         public String toString() {
jaroslav@1890:             Thread o = sync.getOwner();
jaroslav@1890:             return super.toString() + ((o == null) ?
jaroslav@1890:                                        "[Unlocked]" :
jaroslav@1890:                                        "[Locked by thread " + o.getName() + "]");
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Queries if this write lock is held by the current thread.
jaroslav@1890:          * Identical in effect to {@link
jaroslav@1890:          * ReentrantReadWriteLock#isWriteLockedByCurrentThread}.
jaroslav@1890:          *
jaroslav@1890:          * @return {@code true} if the current thread holds this lock and
jaroslav@1890:          *         {@code false} otherwise
jaroslav@1890:          * @since 1.6
jaroslav@1890:          */
jaroslav@1890:         public boolean isHeldByCurrentThread() {
jaroslav@1890:             return sync.isHeldExclusively();
jaroslav@1890:         }
jaroslav@1890: 
jaroslav@1890:         /**
jaroslav@1890:          * Queries the number of holds on this write lock by the current
jaroslav@1890:          * thread.  A thread has a hold on a lock for each lock action
jaroslav@1890:          * that is not matched by an unlock action.  Identical in effect
jaroslav@1890:          * to {@link ReentrantReadWriteLock#getWriteHoldCount}.
jaroslav@1890:          *
jaroslav@1890:          * @return the number of holds on this lock by the current thread,
jaroslav@1890:          *         or zero if this lock is not held by the current thread
jaroslav@1890:          * @since 1.6
jaroslav@1890:          */
jaroslav@1890:         public int getHoldCount() {
jaroslav@1890:             return sync.getWriteHoldCount();
jaroslav@1890:         }
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     // Instrumentation and status
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns {@code true} if this lock has fairness set true.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if this lock has fairness set true
jaroslav@1890:      */
jaroslav@1890:     public final boolean isFair() {
jaroslav@1890:         return sync instanceof FairSync;
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns the thread that currently owns the write lock, or
jaroslav@1890:      * {@code null} if not owned. When this method is called by a
jaroslav@1890:      * thread that is not the owner, the return value reflects a
jaroslav@1890:      * best-effort approximation of current lock status. For example,
jaroslav@1890:      * the owner may be momentarily {@code null} even if there are
jaroslav@1890:      * threads trying to acquire the lock but have not yet done so.
jaroslav@1890:      * This method is designed to facilitate construction of
jaroslav@1890:      * subclasses that provide more extensive lock monitoring
jaroslav@1890:      * facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the owner, or {@code null} if not owned
jaroslav@1890:      */
jaroslav@1890:     protected Thread getOwner() {
jaroslav@1890:         return sync.getOwner();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries the number of read locks held for this lock. This
jaroslav@1890:      * method is designed for use in monitoring system state, not for
jaroslav@1890:      * synchronization control.
jaroslav@1890:      * @return the number of read locks held.
jaroslav@1890:      */
jaroslav@1890:     public int getReadLockCount() {
jaroslav@1890:         return sync.getReadLockCount();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries if the write lock is held by any thread. This method is
jaroslav@1890:      * designed for use in monitoring system state, not for
jaroslav@1890:      * synchronization control.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if any thread holds the write lock and
jaroslav@1890:      *         {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public boolean isWriteLocked() {
jaroslav@1890:         return sync.isWriteLocked();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries if the write lock is held by the current thread.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if the current thread holds the write lock and
jaroslav@1890:      *         {@code false} otherwise
jaroslav@1890:      */
jaroslav@1890:     public boolean isWriteLockedByCurrentThread() {
jaroslav@1890:         return sync.isHeldExclusively();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries the number of reentrant write holds on this lock by the
jaroslav@1890:      * current thread.  A writer thread has a hold on a lock for
jaroslav@1890:      * each lock action that is not matched by an unlock action.
jaroslav@1890:      *
jaroslav@1890:      * @return the number of holds on the write lock by the current thread,
jaroslav@1890:      *         or zero if the write lock is not held by the current thread
jaroslav@1890:      */
jaroslav@1890:     public int getWriteHoldCount() {
jaroslav@1890:         return sync.getWriteHoldCount();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries the number of reentrant read holds on this lock by the
jaroslav@1890:      * current thread.  A reader thread has a hold on a lock for
jaroslav@1890:      * each lock action that is not matched by an unlock action.
jaroslav@1890:      *
jaroslav@1890:      * @return the number of holds on the read lock by the current thread,
jaroslav@1890:      *         or zero if the read lock is not held by the current thread
jaroslav@1890:      * @since 1.6
jaroslav@1890:      */
jaroslav@1890:     public int getReadHoldCount() {
jaroslav@1890:         return sync.getReadHoldCount();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing threads that may be waiting to
jaroslav@1890:      * acquire the write lock.  Because the actual set of threads may
jaroslav@1890:      * change dynamically while constructing this result, the returned
jaroslav@1890:      * collection is only a best-effort estimate.  The elements of the
jaroslav@1890:      * returned collection are in no particular order.  This method is
jaroslav@1890:      * designed to facilitate construction of subclasses that provide
jaroslav@1890:      * more extensive lock monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getQueuedWriterThreads() {
jaroslav@1890:         return sync.getExclusiveQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing threads that may be waiting to
jaroslav@1890:      * acquire the read lock.  Because the actual set of threads may
jaroslav@1890:      * change dynamically while constructing this result, the returned
jaroslav@1890:      * collection is only a best-effort estimate.  The elements of the
jaroslav@1890:      * returned collection are in no particular order.  This method is
jaroslav@1890:      * designed to facilitate construction of subclasses that provide
jaroslav@1890:      * more extensive lock monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getQueuedReaderThreads() {
jaroslav@1890:         return sync.getSharedQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether any threads are waiting to acquire the read or
jaroslav@1890:      * write lock. Note that because cancellations may occur at any
jaroslav@1890:      * time, a {@code true} return does not guarantee that any other
jaroslav@1890:      * thread will ever acquire a lock.  This method is designed
jaroslav@1890:      * primarily for use in monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @return {@code true} if there may be other threads waiting to
jaroslav@1890:      *         acquire the lock
jaroslav@1890:      */
jaroslav@1890:     public final boolean hasQueuedThreads() {
jaroslav@1890:         return sync.hasQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether the given thread is waiting to acquire either
jaroslav@1890:      * the read or write lock. Note that because cancellations may
jaroslav@1890:      * occur at any time, a {@code true} return does not guarantee
jaroslav@1890:      * that this thread will ever acquire a lock.  This method is
jaroslav@1890:      * designed primarily for use in monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @param thread the thread
jaroslav@1890:      * @return {@code true} if the given thread is queued waiting for this lock
jaroslav@1890:      * @throws NullPointerException if the thread is null
jaroslav@1890:      */
jaroslav@1890:     public final boolean hasQueuedThread(Thread thread) {
jaroslav@1890:         return sync.isQueued(thread);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of the number of threads waiting to acquire
jaroslav@1890:      * either the read or write lock.  The value is only an estimate
jaroslav@1890:      * because the number of threads may change dynamically while this
jaroslav@1890:      * method traverses internal data structures.  This method is
jaroslav@1890:      * designed for use in monitoring of the system state, not for
jaroslav@1890:      * synchronization control.
jaroslav@1890:      *
jaroslav@1890:      * @return the estimated number of threads waiting for this lock
jaroslav@1890:      */
jaroslav@1890:     public final int getQueueLength() {
jaroslav@1890:         return sync.getQueueLength();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing threads that may be waiting to
jaroslav@1890:      * acquire either the read or write lock.  Because the actual set
jaroslav@1890:      * of threads may change dynamically while constructing this
jaroslav@1890:      * result, the returned collection is only a best-effort estimate.
jaroslav@1890:      * The elements of the returned collection are in no particular
jaroslav@1890:      * order.  This method is designed to facilitate construction of
jaroslav@1890:      * subclasses that provide more extensive monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getQueuedThreads() {
jaroslav@1890:         return sync.getQueuedThreads();
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Queries whether any threads are waiting on the given condition
jaroslav@1890:      * associated with the write lock. Note that because timeouts and
jaroslav@1890:      * interrupts may occur at any time, a {@code true} return does
jaroslav@1890:      * not guarantee that a future {@code signal} will awaken any
jaroslav@1890:      * threads.  This method is designed primarily for use in
jaroslav@1890:      * monitoring of the system state.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return {@code true} if there are any waiting threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     public boolean hasWaiters(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.hasWaiters((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns an estimate of the number of threads waiting on the
jaroslav@1890:      * given condition associated with the write lock. Note that because
jaroslav@1890:      * timeouts and interrupts may occur at any time, the estimate
jaroslav@1890:      * serves only as an upper bound on the actual number of waiters.
jaroslav@1890:      * This method is designed for use in monitoring of the system
jaroslav@1890:      * state, not for synchronization control.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return the estimated number of waiting threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     public int getWaitQueueLength(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.getWaitQueueLength((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a collection containing those threads that may be
jaroslav@1890:      * waiting on the given condition associated with the write lock.
jaroslav@1890:      * Because the actual set of threads may change dynamically while
jaroslav@1890:      * constructing this result, the returned collection is only a
jaroslav@1890:      * best-effort estimate. The elements of the returned collection
jaroslav@1890:      * are in no particular order.  This method is designed to
jaroslav@1890:      * facilitate construction of subclasses that provide more
jaroslav@1890:      * extensive condition monitoring facilities.
jaroslav@1890:      *
jaroslav@1890:      * @param condition the condition
jaroslav@1890:      * @return the collection of threads
jaroslav@1890:      * @throws IllegalMonitorStateException if this lock is not held
jaroslav@1890:      * @throws IllegalArgumentException if the given condition is
jaroslav@1890:      *         not associated with this lock
jaroslav@1890:      * @throws NullPointerException if the condition is null
jaroslav@1890:      */
jaroslav@1890:     protected Collection<Thread> getWaitingThreads(Condition condition) {
jaroslav@1890:         if (condition == null)
jaroslav@1890:             throw new NullPointerException();
jaroslav@1890:         if (!(condition instanceof AbstractQueuedSynchronizer.ConditionObject))
jaroslav@1890:             throw new IllegalArgumentException("not owner");
jaroslav@1890:         return sync.getWaitingThreads((AbstractQueuedSynchronizer.ConditionObject)condition);
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890:     /**
jaroslav@1890:      * Returns a string identifying this lock, as well as its lock state.
jaroslav@1890:      * The state, in brackets, includes the String {@code "Write locks ="}
jaroslav@1890:      * followed by the number of reentrantly held write locks, and the
jaroslav@1890:      * String {@code "Read locks ="} followed by the number of held
jaroslav@1890:      * read locks.
jaroslav@1890:      *
jaroslav@1890:      * @return a string identifying this lock, as well as its lock state
jaroslav@1890:      */
jaroslav@1890:     public String toString() {
jaroslav@1890:         int c = sync.getCount();
jaroslav@1890:         int w = Sync.exclusiveCount(c);
jaroslav@1890:         int r = Sync.sharedCount(c);
jaroslav@1890: 
jaroslav@1890:         return super.toString() +
jaroslav@1890:             "[Write locks = " + w + ", Read locks = " + r + "]";
jaroslav@1890:     }
jaroslav@1890: 
jaroslav@1890: }