/*
* 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/publicdomain/zero/1.0/
*/
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.
*/
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><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 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());
}
/**
* Returns the value of this {@code AtomicLong} as an {@code int}
* after a narrowing primitive conversion.
*/
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.
*/
public float floatValue() {
return (float)get();
}
/**
* Returns the value of this {@code AtomicLong} as a {@code double}
* after a widening primitive conversion.
*/
public double doubleValue() {
return (double)get();
}
}