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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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package jsr166e.extra; |
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import static java.lang.Double.doubleToRawLongBits; |
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import static java.lang.Double.longBitsToDouble; |
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import sun.misc.Unsafe; |
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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 accumulation, |
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* and 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><a name="bitEquals">This class compares primitive {@code double} |
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* values in methods such as {@link #compareAndSet} by comparing their |
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* bitwise representation using {@link Double#doubleToRawLongBits}, |
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* which differs from both the primitive double {@code ==} operator |
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* and from {@link Double#equals}, as if implemented by: |
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* <pre> {@code |
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* static 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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* @see jsr166e.DoubleAdder |
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* @see jsr166e.DoubleMaxUpdater |
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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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private static final long serialVersionUID = -8405198993435143622L; |
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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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/** |
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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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private transient volatile long value; |
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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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(AtomicDouble.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 AtomicDouble with the given initial value. |
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* Creates a new {@code AtomicDouble} 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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} |
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/** |
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* Creates a new AtomicDouble with initial value {@code 0.0}. |
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* Creates a new {@code AtomicDouble} with initial value {@code 0.0}. |
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*/ |
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public AtomicDouble() { this(0.0); } |
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public AtomicDouble() { |
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// assert doubleToRawLongBits(0.0) == 0L; |
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} |
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/** |
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* Gets the current value. |
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* @param newValue the new value |
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*/ |
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public final void set(double newValue) { |
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value = doubleToRawLongBits(newValue); |
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long next = doubleToRawLongBits(newValue); |
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value = next; |
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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(double newValue) { |
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unsafe.putOrderedLong(this, valueOffset, doubleToRawLongBits(newValue)); |
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long next = doubleToRawLongBits(newValue); |
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unsafe.putOrderedLong(this, valueOffset, next); |
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} |
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/** |
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* @return the previous value |
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*/ |
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public final double getAndSet(double newValue) { |
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long newBits = doubleToRawLongBits(newValue); |
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long next = 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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return longBitsToDouble(currentBits); |
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long current = value; |
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if (unsafe.compareAndSwapLong(this, valueOffset, current, next)) |
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return longBitsToDouble(current); |
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} |
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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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* if the current value is <a href="#bitEquals">bitwise equal</a> |
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* to 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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* @return {@code true} if successful. False return indicates that |
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* the actual value was not bitwise equal to the expected value. |
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*/ |
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public final boolean compareAndSet(double expect, double update) { |
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return unsafe.compareAndSwapLong(this, valueOffset, |
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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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* if the current value is <a href="#bitEquals">bitwise equal</a> |
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* to 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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* <p>May <a |
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* href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious"> |
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* 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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* @return {@code true} if successful |
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*/ |
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public final boolean weakCompareAndSet(double expect, double update) { |
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return compareAndSet(expect, update); |
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*/ |
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public final double getAndAdd(double delta) { |
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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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return longBitsToDouble(currentBits); |
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long current = value; |
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double currentVal = longBitsToDouble(current); |
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double nextVal = currentVal + delta; |
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long next = doubleToRawLongBits(nextVal); |
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if (unsafe.compareAndSwapLong(this, valueOffset, current, next)) |
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return currentVal; |
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} |
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} |
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|
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* @return the updated value |
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*/ |
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public final double addAndGet(double delta) { |
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for (;;) { |
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double current = get(); |
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double next = current + delta; |
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if (compareAndSet(current, next)) |
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return next; |
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while (true) { |
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long current = value; |
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double currentVal = longBitsToDouble(current); |
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double nextVal = currentVal + delta; |
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long next = doubleToRawLongBits(nextVal); |
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if (unsafe.compareAndSwapLong(this, valueOffset, current, next)) |
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return nextVal; |
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} |
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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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* @return the String representation of the current value |
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*/ |
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public String toString() { |
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return Double.toString(get()); |
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} |
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/** |
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* Returns the value of this {@code AtomicDouble} as an {@code int} |
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* after a narrowing primitive conversion. |
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*/ |
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public int intValue() { |
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return (int)get(); |
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return (int) get(); |
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} |
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|
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/** |
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* Returns the value of this {@code AtomicDouble} as a {@code long}. |
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* Returns the value of this {@code AtomicDouble} as a {@code long} |
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> |
* after a narrowing primitive conversion. |
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*/ |
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public long longValue() { |
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< |
return (long)get(); |
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> |
return (long) get(); |
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} |
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|
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/** |
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* Returns the value of this {@code AtomicDouble} as a {@code float} |
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* after a widening primitive conversion. |
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* after a narrowing primitive conversion. |
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*/ |
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public float floatValue() { |
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return (float)get(); |
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> |
return (float) get(); |
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} |
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|
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/** |
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* Returns the value of this {@code AtomicDouble} as a {@code double} |
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* after a widening primitive conversion. |
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> |
* Returns the value of this {@code AtomicDouble} as a {@code double}. |
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*/ |
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public double doubleValue() { |
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return get(); |
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} |
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|
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/** |
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* Saves the state to a stream (that is, serializes it). |
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* |
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* @serialData The current value is emitted (a {@code double}). |
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*/ |
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private void writeObject(java.io.ObjectOutputStream s) |
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throws java.io.IOException{ |
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s.defaultWriteObject(); |
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|
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s.writeDouble(get()); |
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} |
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|
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/** |
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* Reconstitutes the instance from a stream (that is, deserializes it). |
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*/ |
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private void readObject(java.io.ObjectInputStream s) |
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throws java.io.IOException, ClassNotFoundException { |
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s.defaultReadObject(); |
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|
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set(s.readDouble()); |
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} |
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|
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// Unsafe mechanics |
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private static final sun.misc.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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(AtomicDouble.class.getDeclaredField("value")); |
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} catch (Exception ex) { throw new Error(ex); } |
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+ |
} |
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+ |
|
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+ |
/** |
| 247 |
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* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
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* Replace with a simple call to Unsafe.getUnsafe when integrating |
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* into a jdk. |
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+ |
* |
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* @return a sun.misc.Unsafe |
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*/ |
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+ |
private static sun.misc.Unsafe getUnsafe() { |
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+ |
try { |
| 255 |
+ |
return sun.misc.Unsafe.getUnsafe(); |
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+ |
} catch (SecurityException se) { |
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+ |
try { |
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+ |
return java.security.AccessController.doPrivileged |
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+ |
(new java.security |
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+ |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
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+ |
public sun.misc.Unsafe run() throws Exception { |
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+ |
java.lang.reflect.Field f = sun.misc |
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+ |
.Unsafe.class.getDeclaredField("theUnsafe"); |
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+ |
f.setAccessible(true); |
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+ |
return (sun.misc.Unsafe) f.get(null); |
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+ |
}}); |
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+ |
} catch (java.security.PrivilegedActionException e) { |
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+ |
throw new RuntimeException("Could not initialize intrinsics", |
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+ |
e.getCause()); |
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+ |
} |
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} |
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+ |
} |
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} |
