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JDK1.8
// 大部分和AtomicInteger没有太多差别，只标记不同的地方
public class AtomicLong extends Number implements java.io.Serializable {private static final long serialVersionUID = 1927816293512124184L;// setup to use Unsafe.compareAndSwapLong for updates// 通过unsafe来进行更新赋值private static final Unsafe unsafe = Unsafe.getUnsafe();private static final long valueOffset;/*** Records whether the underlying JVM supports lockless* compareAndSwap for longs. While the Unsafe.compareAndSwapLong* method works in either case, some constructions should be* handled at Java level to avoid locking user-visible locks.*/// 这里VM_SUPPORTS_LONG_CAS是一个静态变量，加载时调用VMSupportsCS8方法// VMSupportsCS8判断当前的JVM是否支持无锁的CAS，只调用一次并缓存下来static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8();/*** Returns whether underlying JVM supports lockless CompareAndSet* for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS.*/private static native boolean VMSupportsCS8();static {try {valueOffset = unsafe.objectFieldOffset(AtomicLong.class.getDeclaredField("value"));} catch (Exception ex) { throw new Error(ex); }}private volatile long value;/*** Creates a new AtomicLong with the given initial value.** @param initialValue the initial value*/public AtomicLong(long initialValue) {value = initialValue;}/*** Creates a new AtomicLong with initial value {@code 0}.*/public AtomicLong() {}/*** Gets the current value.** @return the current value*/public final long get() {return value;}/*** Sets to the given value.** @param newValue the new value*/public final void set(long newValue) {value = newValue;}/*** Eventually sets to the given value.** @param newValue the new value* @since 1.6*/public final void lazySet(long newValue) {unsafe.putOrderedLong(this, valueOffset, newValue);}/*** Atomically sets to the given value and returns the old value.** @param newValue the new value* @return the previous value*/public final long getAndSet(long newValue) {return unsafe.getAndSetLong(this, valueOffset, newValue);}/*** Atomically sets the value to the given updated value* if the current value {@code ==} the expected value.** @param expect the expected value* @param update the new value* @return {@code true} if successful. False return indicates that* the actual value was not equal to the expected value.*/public final boolean compareAndSet(long expect, long update) {return unsafe.compareAndSwapLong(this, valueOffset, expect, update);}/*** Atomically sets the value to the given updated value* if the current value {@code ==} the expected value.** <p><a href="package-summary.html#weakCompareAndSet">May fail* spuriously and does not provide ordering guarantees</a>, so is* only rarely an appropriate alternative to {@code compareAndSet}.** @param expect the expected value* @param update the new value* @return {@code true} if successful*/public final boolean weakCompareAndSet(long expect, long update) {return unsafe.compareAndSwapLong(this, valueOffset, expect, update);}/*** Atomically increments by one the current value.** @return the previous value*/public final long getAndIncrement() {return unsafe.getAndAddLong(this, valueOffset, 1L);}/*** Atomically decrements by one the current value.** @return the previous value*/public final long getAndDecrement() {return unsafe.getAndAddLong(this, valueOffset, -1L);}/*** Atomically adds the given value to the current value.** @param delta the value to add* @return the previous value*/public final long getAndAdd(long delta) {return unsafe.getAndAddLong(this, valueOffset, delta);}/*** Atomically increments by one the current value.** @return the updated value*/public final long incrementAndGet() {return unsafe.getAndAddLong(this, valueOffset, 1L) + 1L;}/*** Atomically decrements by one the current value.** @return the updated value*/public final long decrementAndGet() {return unsafe.getAndAddLong(this, valueOffset, -1L) - 1L;}/*** Atomically adds the given value to the current value.** @param delta the value to add* @return the updated value*/public final long addAndGet(long delta) {return unsafe.getAndAddLong(this, valueOffset, delta) + delta;}/*** Atomically updates the current value with the results of* applying the given function, returning the previous value. The* function should be side-effect-free, since it may be re-applied* when attempted updates fail due to contention among threads.** @param updateFunction a side-effect-free function* @return the previous value* @since 1.8*/public final long getAndUpdate(LongUnaryOperator updateFunction) {long prev, next;do {prev = get();next = updateFunction.applyAsLong(prev);} while (!compareAndSet(prev, next));return prev;}/*** Atomically updates the current value with the results of* applying the given function, returning the updated value. The* function should be side-effect-free, since it may be re-applied* when attempted updates fail due to contention among threads.** @param updateFunction a side-effect-free function* @return the updated value* @since 1.8*/public final long updateAndGet(LongUnaryOperator updateFunction) {long prev, next;do {prev = get();next = updateFunction.applyAsLong(prev);} while (!compareAndSet(prev, next));return next;}/*** Atomically updates the current value with the results of* applying the given function to the current and given values,* returning the previous value. The function should be* side-effect-free, since it may be re-applied when attempted* updates fail due to contention among threads. The function* is applied with the current value as its first argument,* and the given update as the second argument.** @param x the update value* @param accumulatorFunction a side-effect-free function of two arguments* @return the previous value* @since 1.8*/public final long getAndAccumulate(long x,LongBinaryOperator accumulatorFunction) {long prev, next;do {prev = get();next = accumulatorFunction.applyAsLong(prev, x);} while (!compareAndSet(prev, next));return prev;}/*** Atomically updates the current value with the results of* applying the given function to the current and given values,* returning the updated value. The function should be* side-effect-free, since it may be re-applied when attempted* updates fail due to contention among threads. The function* is applied with the current value as its first argument,* and the given update as the second argument.** @param x the update value* @param accumulatorFunction a side-effect-free function of two arguments* @return the updated value* @since 1.8*/public final long accumulateAndGet(long x,LongBinaryOperator accumulatorFunction) {long prev, next;do {prev = get();next = accumulatorFunction.applyAsLong(prev, x);} while (!compareAndSet(prev, next));return next;}/*** Returns the String representation of the current value.* @return the String representation of the current value*/public String toString() {return Long.toString(get());}/*** Returns the value of this {@code AtomicLong} as an {@code int}* after a narrowing primitive conversion.* @jls 5.1.3 Narrowing Primitive Conversions*/public int intValue() {return (int)get();}/*** Returns the value of this {@code AtomicLong} as a {@code long}.*/public long longValue() {return get();}/*** Returns the value of this {@code AtomicLong} as a {@code float}* after a widening primitive conversion.* @jls 5.1.2 Widening Primitive Conversions*/public float floatValue() {return (float)get();}/*** Returns the value of this {@code AtomicLong} as a {@code double}* after a widening primitive conversion.* @jls 5.1.2 Widening Primitive Conversions*/public double doubleValue() {return (double)get();}}
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