| /* |
| * Written by Doug Lea with assistance from members of JCP JSR-166 |
| * Expert Group and released to the public domain, as explained at |
| * http://creativecommons.org/licenses/publicdomain |
| */ |
| |
| 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 |
| * 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. |
| * |
| * Initialised in the static block. |
| */ |
| static final boolean VM_SUPPORTS_LONG_CAS; |
| |
| /** |
| * 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); } |
| |
| boolean longCASSupport; |
| try { |
| longCASSupport = VMSupportsCS8(); |
| } catch (UnsatisfiedLinkError e) { |
| // assume there's support if the native isn't provided by the VM |
| longCASSupport = true; |
| } |
| VM_SUPPORTS_LONG_CAS = longCASSupport; |
| } |
| |
| 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; |
| } |
| |
| /** |
| * 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 get(); |
| } |
| |
| public float floatValue() { |
| return (float)get(); |
| } |
| |
| public double doubleValue() { |
| return (double)get(); |
| } |
| |
| } |