/*
* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*
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/*
*
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* 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 java.util.function.
LongUnaryOperator;
import java.util.function.
LongBinaryOperator;
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) {
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();
}
}