/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
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*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* 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.lang.invoke.VarHandle;
import java.util.function.LongBinaryOperator;
import java.util.function.LongUnaryOperator;
/**
* A {@code long} value that may be updated atomically. See the
* {@link VarHandle} specification for descriptions of the properties
* of atomic accesses. 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;
/**
* Records whether the underlying JVM supports lockless
* compareAndSwap for longs. While the intrinsic 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();
/*
* This class intended to be implemented using VarHandles, but there
* are unresolved cyclic startup dependencies.
*/
private static final jdk.internal.misc.Unsafe U = jdk.internal.misc.Unsafe.getUnsafe();
private static final long VALUE;
static {
try {
VALUE = U.objectFieldOffset
(AtomicLong.class.getDeclaredField("value"));
} catch (ReflectiveOperationException e) {
throw new Error(e);
}
}
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() {
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getVolatile}.
*
* @return the current value
*/
public final long get() {
return value;
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setVolatile}.
*
* @param newValue the new value
*/
public final void set(long newValue) {
// Use putLongVolatile instead of ordinary volatile store when
// using compareAndSwapLong, for sake of some 32bit systems.
U.putLongVolatile(this, VALUE, newValue);
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(long newValue) {
U.putLongRelease(this, VALUE, newValue);
}
/**
* Atomically sets the value to {@code newValue} and returns the old value,
* with memory effects as specified by {@link VarHandle#getAndSet}.
*
* @param newValue the new value
* @return the previous value
*/
public final long getAndSet(long newValue) {
return U.getAndSetLong(this, VALUE, newValue);
}
/**
* Atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#compareAndSet}.
*
* @param expectedValue the expected value
* @param newValue 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 expectedValue, long newValue) {
return U.compareAndSwapLong(this, VALUE, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
*
* @deprecated This method has plain memory effects but the method
* name implies volatile memory effects (see methods such as
* {@link #compareAndExchange} and {@link #compareAndSet}). To avoid
* confusion over plain or volatile memory effects it is recommended that
* the method {@link #weakCompareAndSetPlain} be used instead.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @see #weakCompareAndSetPlain
*/
@Deprecated(since="9")
public final boolean weakCompareAndSet(long expectedValue, long newValue) {
return U.weakCompareAndSwapLong(this, VALUE, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by {@link VarHandle#weakCompareAndSetPlain}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetPlain(long expectedValue, long newValue) {
return U.weakCompareAndSwapLong(this, VALUE, expectedValue, newValue);
}
/**
* Atomically increments the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* <p>Equivalent to {@code getAndAdd(1)}.
*
* @return the previous value
*/
public final long getAndIncrement() {
return U.getAndAddLong(this, VALUE, 1L);
}
/**
* Atomically decrements the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* <p>Equivalent to {@code getAndAdd(-1)}.
*
* @return the previous value
*/
public final long getAndDecrement() {
return U.getAndAddLong(this, VALUE, -1L);
}
/**
* Atomically adds the given value to the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* @param delta the value to add
* @return the previous value
*/
public final long getAndAdd(long delta) {
return U.getAndAddLong(this, VALUE, delta);
}
/**
* Atomically increments the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* <p>Equivalent to {@code addAndGet(1)}.
*
* @return the updated value
*/
public final long incrementAndGet() {
return U.getAndAddLong(this, VALUE, 1L) + 1L;
}
/**
* Atomically decrements the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* <p>Equivalent to {@code addAndGet(-1)}.
*
* @return the updated value
*/
public final long decrementAndGet() {
return U.getAndAddLong(this, VALUE, -1L) - 1L;
}
/**
* Atomically adds the given value to the current value,
* with memory effects as specified by {@link VarHandle#getAndAdd}.
*
* @param delta the value to add
* @return the updated value
*/
public final long addAndGet(long delta) {
return U.getAndAddLong(this, VALUE, 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 = get(), next = 0L;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.applyAsLong(prev);
if (weakCompareAndSetVolatile(prev, next))
return prev;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = 0L;
for (boolean haveNext = false;;) {
if (!haveNext)
next = updateFunction.applyAsLong(prev);
if (weakCompareAndSetVolatile(prev, next))
return next;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = 0L;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.applyAsLong(prev, x);
if (weakCompareAndSetVolatile(prev, next))
return prev;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 = get(), next = 0L;
for (boolean haveNext = false;;) {
if (!haveNext)
next = accumulatorFunction.applyAsLong(prev, x);
if (weakCompareAndSetVolatile(prev, next))
return next;
haveNext = (prev == (prev = get()));
}
}
/**
* 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 current value of this {@code AtomicLong} as an {@code int}
* after a narrowing primitive conversion,
* with memory effects as specified by {@link VarHandle#getVolatile}.
* @jls 5.1.3 Narrowing Primitive Conversions
*/
public int intValue() {
return (int)get();
}
/**
* Returns the current value of this {@code AtomicLong} as a {@code long},
* with memory effects as specified by {@link VarHandle#getVolatile}.
* Equivalent to {@link #get()}.
*/
public long longValue() {
return get();
}
/**
* Returns the current value of this {@code AtomicLong} as a {@code float}
* after a widening primitive conversion,
* with memory effects as specified by {@link VarHandle#getVolatile}.
* @jls 5.1.2 Widening Primitive Conversions
*/
public float floatValue() {
return (float)get();
}
/**
* Returns the current value of this {@code AtomicLong} as a {@code double}
* after a widening primitive conversion,
* with memory effects as specified by {@link VarHandle#getVolatile}.
* @jls 5.1.2 Widening Primitive Conversions
*/
public double doubleValue() {
return (double)get();
}
// jdk9
/**
* Returns the current value, with memory semantics of reading as if the
* variable was declared non-{@code volatile}.
*
* @return the value
* @since 9
*/
public final long getPlain() {
return U.getLong(this, VALUE);
}
/**
* Sets the value to {@code newValue}, with memory semantics
* of setting as if the variable was declared non-{@code volatile}
* and non-{@code final}.
*
* @param newValue the new value
* @since 9
*/
public final void setPlain(long newValue) {
U.putLong(this, VALUE, newValue);
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getOpaque}.
*
* @return the value
* @since 9
*/
public final long getOpaque() {
return U.getLongOpaque(this, VALUE);
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setOpaque}.
*
* @param newValue the new value
* @since 9
*/
public final void setOpaque(long newValue) {
U.putLongOpaque(this, VALUE, newValue);
}
/**
* Returns the current value,
* with memory effects as specified by {@link VarHandle#getAcquire}.
*
* @return the value
* @since 9
*/
public final long getAcquire() {
return U.getLongAcquire(this, VALUE);
}
/**
* Sets the value to {@code newValue},
* with memory effects as specified by {@link VarHandle#setRelease}.
*
* @param newValue the new value
* @since 9
*/
public final void setRelease(long newValue) {
U.putLongRelease(this, VALUE, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchange}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final long compareAndExchange(long expectedValue, long newValue) {
return U.compareAndExchangeLongVolatile(this, VALUE, expectedValue, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeAcquire}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final long compareAndExchangeAcquire(long expectedValue, long newValue) {
return U.compareAndExchangeLongAcquire(this, VALUE, expectedValue, newValue);
}
/**
* Atomically sets the value to {@code newValue} if the current value,
* referred to as the <em>witness value</em>, {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#compareAndExchangeRelease}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return the witness value, which will be the same as the
* expected value if successful
* @since 9
*/
public final long compareAndExchangeRelease(long expectedValue, long newValue) {
return U.compareAndExchangeLongRelease(this, VALUE, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSet}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetVolatile(long expectedValue, long newValue) {
return U.weakCompareAndSwapLongVolatile(this, VALUE, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetAcquire}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetAcquire(long expectedValue, long newValue) {
return U.weakCompareAndSwapLongAcquire(this, VALUE, expectedValue, newValue);
}
/**
* Possibly atomically sets the value to {@code newValue}
* if the current value {@code == expectedValue},
* with memory effects as specified by
* {@link VarHandle#weakCompareAndSetRelease}.
*
* @param expectedValue the expected value
* @param newValue the new value
* @return {@code true} if successful
* @since 9
*/
public final boolean weakCompareAndSetRelease(long expectedValue, long newValue) {
return U.weakCompareAndSwapLongRelease(this, VALUE, expectedValue, newValue);
}
}