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/* * @(#)AtomicLong.java 1.12 06/06/15 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package java.util.concurrent.atomic; import sun.misc.Unsafe; /** * A {@code long} value that may be updated atomically. See the * {@link java.util.concurrent.atomic} package specification for * description of the properties of atomic variables. An * {@code AtomicLong} is used in applications such as atomically * incremented sequence numbers, and cannot be used as a replacement * for a {@link java.lang.Long}. However, this class does extend * {@code Number} to allow uniform access by tools and utilities that * deal with numerically-based classes. * * @since 1.5 * @author Doug Lea */ public class AtomicLong extends Number implements java.io.Serializable { private static final long serialVersionUID = 1927816293512124184L; // setup to use Unsafe.compareAndSwapLong for updates private static final Unsafe unsafe = Unsafe.getUnsafe(); private static final long valueOffset; /** * Records whether the underlying JVM supports lockless * CompareAndSet for longs. While the unsafe.CompareAndSetLong * method works in either case, some constructions should be * handled at Java level to avoid locking user-visible locks. */ 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) { while (true) { long current = get(); if (compareAndSet(current, newValue)) return current; } } /** * 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 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>May <a href="package-summary.html#Spurious">fail spuriously</a> * and does not provide ordering guarantees, so is only rarely an * appropriate alternative to {@code compareAndSet}. * * @param expect the expected value * @param update the new value * @return 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() { while (true) { long current = get(); long next = current + 1; if (compareAndSet(current, next)) return current; } } /** * Atomically decrements by one the current value. * * @return the previous value */ public final long getAndDecrement() { while (true) { long current = get(); long next = current - 1; if (compareAndSet(current, next)) return current; } } /** * 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) { while (true) { long current = get(); long next = current + delta; if (compareAndSet(current, next)) return current; } } /** * Atomically increments by one the current value. * * @return the updated value */ public final long incrementAndGet() { for (;;) { long current = get(); long next = current + 1; if (compareAndSet(current, next)) return next; } } /** * Atomically decrements by one the current value. * * @return the updated value */ public final long decrementAndGet() { for (;;) { long current = get(); long next = current - 1; if (compareAndSet(current, next)) return next; } } /** * 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) { for (;;) { long current = get(); long next = current + delta; if (compareAndSet(current, 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()); } public int intValue() { return (int)get(); } public long longValue() { return (long)get(); } public float floatValue() { return (float)get(); } public double doubleValue() { return (double)get(); } }