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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. Use, modify, and |
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* redistribute this code in any way without acknowledgement. |
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*/ |
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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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/** |
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* An AtomicInteger maintains an <tt>int</tt> value that is updated |
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* atomically. |
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* @since 1.5 |
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* @author Doug Lea |
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*/ |
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public final class AtomicInteger implements java.io.Serializable { |
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// setup to use Unsafe.compareAndSwapInt 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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static { |
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try { |
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valueOffset = unsafe.objectFieldOffset |
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(AtomicInteger.class.getDeclaredField("value")); |
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} |
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catch(Exception ex) { throw new Error(ex); } |
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} |
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|
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private volatile int value; |
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|
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/** |
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* Create a new AtomicInteger with the given initial value; |
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* @param initialValue the initial value |
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*/ |
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public AtomicInteger(int initialValue) { |
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value = initialValue; |
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} |
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|
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/** |
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* Get the current value |
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* @return the current value |
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*/ |
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public int get() { |
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return value; |
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} |
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|
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/** |
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* Set to the given value |
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* @param newValue the new value |
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*/ |
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public void set(int newValue) { |
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value = newValue; |
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} |
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|
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/** |
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* Set to the give value and return the old value |
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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 int getAndSet(int newValue) { |
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for (;;) { |
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int current = get(); |
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if (compareAndSet(current, newValue)) |
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return current; |
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} |
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} |
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|
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/** |
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* Atomically increment the current value. |
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* @return the previous value; |
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*/ |
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public int getAndIncrement() { |
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for (;;) { |
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int current = get(); |
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int next = current + 1; |
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if (compareAndSet(current, next)) |
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return current; |
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} |
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} |
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|
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|
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/** |
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* Atomically decrement the current value. |
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* @return the previous value; |
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*/ |
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public int getAndDecrement() { |
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for (;;) { |
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int current = get(); |
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int next = current - 1; |
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if (compareAndSet(current, next)) |
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return current; |
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} |
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} |
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|
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|
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/** |
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* Atomically add the given value to current value. |
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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 int getAndAdd(int delta) { |
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for (;;) { |
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int current = get(); |
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int next = current + delta; |
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if (compareAndSet(current, next)) |
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return current; |
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} |
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} |
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|
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|
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/** |
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* Atomically set the value to the given updated value |
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* if the current value <tt>==</tt> the expected value. |
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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 boolean compareAndSet(int expect, int update) { |
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return unsafe.compareAndSwapInt(this, valueOffset, expect, update); |
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} |
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|
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/** |
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* Atomically set the value to the given updated value |
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* if the current value <tt>==</tt> the expected value. |
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* May fail spuriously. |
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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 boolean weakCompareAndSet(int expect, int update) { |
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return unsafe.compareAndSwapInt(this, valueOffset, expect, update); |
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} |
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|
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} |
