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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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* Written by Doug Lea and Martin Buchholz with assistance from |
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* members of JCP JSR-166 Expert Group and released to the public |
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* domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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/** |
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* A {@code double} 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 AtomicDouble} 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.Double}. 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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* description of the properties of atomic variables. An {@code |
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* AtomicDouble} is used in applications such as atomic summation, and |
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* cannot be used as a replacement for a {@link Double}. However, |
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* this class does extend {@code Number} to allow uniform access by |
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* tools and utilities that deal with numerically-based classes. |
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* |
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* <p>This class differs from the primitive double {@code ==} operator |
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* and from {@link Double#equals} in that it uses purely bitwise |
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* equality in methods such as {@link #compareAndSet}, as if |
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* implemented by: |
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* <pre> {@code |
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* boolean bitEquals(double x, double y) { |
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* long xBits = Double.doubleToRawLongBits(x); |
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* long yBits = Double.doubleToRawLongBits(y); |
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* return xBits == yBits; |
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* }}</pre> |
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* |
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* @since 1.5 |
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* @author Doug Lea |
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* @author Martin Buchholz |
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*/ |
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public class AtomicDouble extends Number implements java.io.Serializable { |
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private static final long serialVersionUID = 1927816293512124184L; |
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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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private static boolean VMSupportsCS8() { |
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try { |
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Class<?> klazz = java.util.concurrent.atomic.AtomicLong.class; |
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java.lang.reflect.Method m = |
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klazz.getDeclaredMethod("VMSupportsCS8", new Class<?>[0]); |
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m.setAccessible(true); |
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return (Boolean) m.invoke(new Class<?>[0]); |
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} catch (Throwable t) { throw new Error(t); } |
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} |
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static { |
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try { |
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long newBits = doubleToRawLongBits(newValue); |
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while (true) { |
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long currentBits = value; |
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if (compareAndSet(currentBits, newBits)) |
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if (unsafe.compareAndSwapLong(this, valueOffset, |
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currentBits, newBits)) |
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return longBitsToDouble(currentBits); |
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} |
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} |
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while (true) { |
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long currentBits = value; |
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long nextBits = doubleToRawLongBits(longBitsToDouble(currentBits) + delta); |
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if (compareAndSet(currentBits, nextBits)) |
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if (unsafe.compareAndSwapLong(this, valueOffset, |
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currentBits, nextBits)) |
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return longBitsToDouble(currentBits); |
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} |
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} |
