author | chegar |
Thu, 10 Jan 2013 21:52:38 +0000 | |
changeset 15020 | 50394fa17c1b |
parent 14325 | 622c473a21aa |
child 15267 | c884f548a25f |
permissions | -rw-r--r-- |
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/* |
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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* |
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* This code is free software; you can redistribute it and/or modify it |
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* under the terms of the GNU General Public License version 2 only, as |
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* published by the Free Software Foundation. Oracle designates this |
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* particular file as subject to the "Classpath" exception as provided |
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* by Oracle in the LICENSE file that accompanied this code. |
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* |
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* This code is distributed in the hope that it will be useful, but WITHOUT |
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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* version 2 for more details (a copy is included in the LICENSE file that |
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* accompanied this code). |
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* |
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* You should have received a copy of the GNU General Public License version |
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* 2 along with this work; if not, write to the Free Software Foundation, |
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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* |
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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* or visit www.oracle.com if you need additional information or have any |
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* questions. |
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*/ |
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/* |
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* This file is available under and governed by the GNU General Public |
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* License version 2 only, as published by the Free Software Foundation. |
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* However, the following notice accompanied the original version of this |
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* file: |
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* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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package java.util.concurrent.atomic; |
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import sun.misc.Unsafe; |
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/** |
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* A {@code long} value that may be updated atomically. See the |
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* {@link java.util.concurrent.atomic} package specification for |
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* description of the properties of atomic variables. An |
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* {@code AtomicLong} is used in applications such as atomically |
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* incremented sequence numbers, and cannot be used as a replacement |
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* for a {@link java.lang.Long}. However, this class does extend |
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* {@code Number} to allow uniform access by tools and utilities that |
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* deal with numerically-based classes. |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public class AtomicLong extends Number implements java.io.Serializable { |
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private static final long serialVersionUID = 1927816293512124184L; |
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// setup to use Unsafe.compareAndSwapLong for updates |
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private static final Unsafe unsafe = Unsafe.getUnsafe(); |
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private static final long valueOffset; |
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/** |
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* Records whether the underlying JVM supports lockless |
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* compareAndSwap for longs. While the Unsafe.compareAndSwapLong |
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* method works in either case, some constructions should be |
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* handled at Java level to avoid locking user-visible locks. |
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*/ |
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static final boolean VM_SUPPORTS_LONG_CAS = VMSupportsCS8(); |
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/** |
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* Returns whether underlying JVM supports lockless CompareAndSet |
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* for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS. |
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*/ |
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private static native boolean VMSupportsCS8(); |
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static { |
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try { |
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valueOffset = unsafe.objectFieldOffset |
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(AtomicLong.class.getDeclaredField("value")); |
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} catch (Exception ex) { throw new Error(ex); } |
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} |
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private volatile long value; |
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/** |
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* Creates a new AtomicLong with the given initial value. |
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* |
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* @param initialValue the initial value |
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*/ |
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public AtomicLong(long initialValue) { |
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value = initialValue; |
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} |
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/** |
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* Creates a new AtomicLong with initial value {@code 0}. |
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*/ |
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public AtomicLong() { |
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} |
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/** |
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* Gets the current value. |
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* |
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* @return the current value |
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*/ |
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public final long get() { |
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return value; |
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} |
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/** |
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* Sets to the given value. |
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* |
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* @param newValue the new value |
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*/ |
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public final void set(long newValue) { |
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value = newValue; |
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} |
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/** |
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* Eventually sets to the given value. |
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* |
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* @param newValue the new value |
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* @since 1.6 |
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*/ |
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public final void lazySet(long newValue) { |
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unsafe.putOrderedLong(this, valueOffset, newValue); |
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} |
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/** |
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* Atomically sets to the given value and returns the old value. |
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* |
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* @param newValue the new value |
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* @return the previous value |
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*/ |
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public final long getAndSet(long newValue) { |
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return unsafe.getAndSetLong(this, valueOffset, newValue); |
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} |
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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} the expected value. |
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* |
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* @param expect the expected value |
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* @param update the new value |
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* @return true if successful. False return indicates that |
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* the actual value was not equal to the expected value. |
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*/ |
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public final boolean compareAndSet(long expect, long update) { |
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return unsafe.compareAndSwapLong(this, valueOffset, expect, update); |
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} |
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/** |
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* Atomically sets the value to the given updated value |
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* if the current value {@code ==} the expected value. |
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* |
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* <p>May <a href="package-summary.html#Spurious">fail spuriously</a> |
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* and does not provide ordering guarantees, so is only rarely an |
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* appropriate alternative to {@code compareAndSet}. |
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* |
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* @param expect the expected value |
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* @param update the new value |
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* @return true if successful |
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*/ |
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public final boolean weakCompareAndSet(long expect, long update) { |
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return unsafe.compareAndSwapLong(this, valueOffset, expect, update); |
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} |
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/** |
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* Atomically increments by one the current value. |
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* |
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* @return the previous value |
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*/ |
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public final long getAndIncrement() { |
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return getAndAdd(1); |
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} |
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/** |
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* Atomically decrements by one the current value. |
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* |
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* @return the previous value |
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*/ |
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public final long getAndDecrement() { |
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return getAndAdd(-1); |
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} |
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/** |
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* Atomically adds the given value to the current value. |
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* |
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* @param delta the value to add |
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* @return the previous value |
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*/ |
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public final long getAndAdd(long delta) { |
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return unsafe.getAndAddLong(this, valueOffset, delta); |
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} |
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/** |
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* Atomically increments by one the current value. |
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* |
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* @return the updated value |
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*/ |
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public final long incrementAndGet() { |
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return getAndAdd(1) + 1; |
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} |
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/** |
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* Atomically decrements by one the current value. |
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* |
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* @return the updated value |
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*/ |
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public final long decrementAndGet() { |
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return getAndAdd(-1) - 1; |
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} |
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/** |
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* Atomically adds the given value to the current value. |
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* |
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* @param delta the value to add |
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* @return the updated value |
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*/ |
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public final long addAndGet(long delta) { |
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return getAndAdd(delta) + delta; |
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} |
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/** |
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* Returns the String representation of the current value. |
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* @return the String representation of the current value |
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*/ |
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public String toString() { |
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return Long.toString(get()); |
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} |
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/** |
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* Returns the value of this {@code AtomicLong} as an {@code int} |
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* after a narrowing primitive conversion. |
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* @jls 5.1.3 Narrowing Primitive Conversions |
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*/ |
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public int intValue() { |
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return (int)get(); |
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} |
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/** |
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* Returns the value of this {@code AtomicLong} as a {@code long}. |
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*/ |
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public long longValue() { |
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return get(); |
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} |
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/** |
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* Returns the value of this {@code AtomicLong} as a {@code float} |
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* after a widening primitive conversion. |
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* @jls 5.1.2 Widening Primitive Conversions |
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*/ |
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public float floatValue() { |
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return (float)get(); |
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} |
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/** |
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* Returns the value of this {@code AtomicLong} as a {@code double} |
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* after a widening primitive conversion. |
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* @jls 5.1.2 Widening Primitive Conversions |
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*/ |
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public double doubleValue() { |
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return (double)get(); |
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} |
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} |