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31 * Written by Doug Lea with assistance from members of JCP JSR-166
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36 package java.util.concurrent.atomic;
39 * A {@code long} value that may be updated atomically. See the
40 * {@link java.util.concurrent.atomic} package specification for
41 * description of the properties of atomic variables. An
42 * {@code AtomicLong} is used in applications such as atomically
43 * incremented sequence numbers, and cannot be used as a replacement
44 * for a {@link java.lang.Long}. However, this class does extend
45 * {@code Number} to allow uniform access by tools and utilities that
46 * deal with numerically-based classes.
51 public class AtomicLong extends Number implements java.io.Serializable {
52 private static final long serialVersionUID = 1927816293512124184L;
56 * Returns whether underlying JVM supports lockless CompareAndSet
57 * for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.
59 private static native boolean VMSupportsCS8();
61 private volatile long value;
64 * Creates a new AtomicLong with the given initial value.
66 * @param initialValue the initial value
68 public AtomicLong(long initialValue) {
73 * Creates a new AtomicLong with initial value {@code 0}.
79 * Gets the current value.
81 * @return the current value
83 public final long get() {
88 * Sets to the given value.
90 * @param newValue the new value
92 public final void set(long newValue) {
97 * Eventually sets to the given value.
99 * @param newValue the new value
102 public final void lazySet(long newValue) {
107 * Atomically sets to the given value and returns the old value.
109 * @param newValue the new value
110 * @return the previous value
112 public final long getAndSet(long newValue) {
114 long current = get();
115 if (compareAndSet(current, newValue))
121 * Atomically sets the value to the given updated value
122 * if the current value {@code ==} the expected value.
124 * @param expect the expected value
125 * @param update the new value
126 * @return true if successful. False return indicates that
127 * the actual value was not equal to the expected value.
129 public final boolean compareAndSet(long expect, long update) {
130 if (value == expect) {
139 * Atomically sets the value to the given updated value
140 * if the current value {@code ==} the expected value.
142 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
143 * and does not provide ordering guarantees, so is only rarely an
144 * appropriate alternative to {@code compareAndSet}.
146 * @param expect the expected value
147 * @param update the new value
148 * @return true if successful.
150 public final boolean weakCompareAndSet(long expect, long update) {
151 return compareAndSet(expect, update);
155 * Atomically increments by one the current value.
157 * @return the previous value
159 public final long getAndIncrement() {
161 long current = get();
162 long next = current + 1;
163 if (compareAndSet(current, next))
169 * Atomically decrements by one the current value.
171 * @return the previous value
173 public final long getAndDecrement() {
175 long current = get();
176 long next = current - 1;
177 if (compareAndSet(current, next))
183 * Atomically adds the given value to the current value.
185 * @param delta the value to add
186 * @return the previous value
188 public final long getAndAdd(long delta) {
190 long current = get();
191 long next = current + delta;
192 if (compareAndSet(current, next))
198 * Atomically increments by one the current value.
200 * @return the updated value
202 public final long incrementAndGet() {
204 long current = get();
205 long next = current + 1;
206 if (compareAndSet(current, next))
212 * Atomically decrements by one the current value.
214 * @return the updated value
216 public final long decrementAndGet() {
218 long current = get();
219 long next = current - 1;
220 if (compareAndSet(current, next))
226 * Atomically adds the given value to the current value.
228 * @param delta the value to add
229 * @return the updated value
231 public final long addAndGet(long delta) {
233 long current = get();
234 long next = current + delta;
235 if (compareAndSet(current, next))
241 * Returns the String representation of the current value.
242 * @return the String representation of the current value.
244 public String toString() {
245 return Long.toString(get());
249 public int intValue() {
253 public long longValue() {
257 public float floatValue() {
261 public double doubleValue() {
262 return (double)get();