| 1 |
|
/* |
| 2 |
< |
* Written by Doug Lea with assistance from members of JCP JSR-166 |
| 3 |
< |
* Expert Group and released to the public domain, as explained at |
| 2 |
> |
* Written by Doug Lea and Martin Buchholz with assistance from |
| 3 |
> |
* members of JCP JSR-166 Expert Group and released to the public |
| 4 |
> |
* domain, as explained at |
| 5 |
|
* http://creativecommons.org/publicdomain/zero/1.0/ |
| 6 |
|
*/ |
| 7 |
|
|
| 8 |
|
package jsr166e.extra; |
| 9 |
|
import static java.lang.Double.doubleToRawLongBits; |
| 10 |
|
import static java.lang.Double.longBitsToDouble; |
| 10 |
– |
import sun.misc.Unsafe; |
| 11 |
|
|
| 12 |
|
/** |
| 13 |
|
* A {@code double} value that may be updated atomically. See the |
| 14 |
|
* {@link java.util.concurrent.atomic} package specification for |
| 15 |
< |
* description of the properties of atomic variables. An |
| 16 |
< |
* {@code AtomicDouble} is used in applications such as atomically |
| 17 |
< |
* incremented sequence numbers, and cannot be used as a replacement |
| 18 |
< |
* for a {@link java.lang.Double}. However, this class does extend |
| 19 |
< |
* {@code Number} to allow uniform access by tools and utilities that |
| 20 |
< |
* deal with numerically-based classes. |
| 15 |
> |
* description of the properties of atomic variables. An {@code |
| 16 |
> |
* AtomicDouble} is used in applications such as atomic accumulation, |
| 17 |
> |
* and cannot be used as a replacement for a {@link Double}. However, |
| 18 |
> |
* this class does extend {@code Number} to allow uniform access by |
| 19 |
> |
* tools and utilities that deal with numerically-based classes. |
| 20 |
> |
* |
| 21 |
> |
* <p>This class differs from the primitive double {@code ==} operator |
| 22 |
> |
* and from {@link Double#equals} in that it uses purely bitwise |
| 23 |
> |
* equality in methods such as {@link #compareAndSet}, as if |
| 24 |
> |
* implemented by: |
| 25 |
> |
* <pre> {@code |
| 26 |
> |
* boolean bitEquals(double x, double y) { |
| 27 |
> |
* long xBits = Double.doubleToRawLongBits(x); |
| 28 |
> |
* long yBits = Double.doubleToRawLongBits(y); |
| 29 |
> |
* return xBits == yBits; |
| 30 |
> |
* }}</pre> |
| 31 |
|
* |
| 22 |
– |
* @since 1.5 |
| 32 |
|
* @author Doug Lea |
| 33 |
+ |
* @author Martin Buchholz |
| 34 |
|
*/ |
| 35 |
|
public class AtomicDouble extends Number implements java.io.Serializable { |
| 36 |
< |
private static final long serialVersionUID = 1927816293512124184L; |
| 36 |
> |
static final long serialVersionUID = -8405198993435143622L; |
| 37 |
|
|
| 38 |
|
// setup to use Unsafe.compareAndSwapLong for updates |
| 39 |
< |
private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| 39 |
> |
private static final sun.misc.Unsafe unsafe = getUnsafe(); |
| 40 |
|
private static final long valueOffset; |
| 41 |
|
|
| 42 |
|
/** |
| 51 |
|
* Returns whether underlying JVM supports lockless CompareAndSet |
| 52 |
|
* for longs. Called only once and cached in VM_SUPPORTS_LONG_CAS. |
| 53 |
|
*/ |
| 54 |
< |
private static native boolean VMSupportsCS8(); |
| 54 |
> |
private static boolean VMSupportsCS8() { |
| 55 |
> |
final Class<?> klazz = java.util.concurrent.atomic.AtomicLong.class; |
| 56 |
> |
return java.security.AccessController.doPrivileged |
| 57 |
> |
(new java.security.PrivilegedAction<Boolean>() { |
| 58 |
> |
public Boolean run() { |
| 59 |
> |
try { |
| 60 |
> |
java.lang.reflect.Method m = |
| 61 |
> |
klazz.getDeclaredMethod("VMSupportsCS8", new Class<?>[0]); |
| 62 |
> |
m.setAccessible(true); |
| 63 |
> |
return (Boolean) m.invoke(new Class<?>[0]); |
| 64 |
> |
} catch (Throwable t) { throw new Error(t); } |
| 65 |
> |
}}); |
| 66 |
> |
} |
| 67 |
|
|
| 68 |
|
static { |
| 69 |
|
try { |
| 110 |
|
* Eventually sets to the given value. |
| 111 |
|
* |
| 112 |
|
* @param newValue the new value |
| 91 |
– |
* @since 1.6 |
| 113 |
|
*/ |
| 114 |
|
public final void lazySet(double newValue) { |
| 115 |
|
unsafe.putOrderedLong(this, valueOffset, doubleToRawLongBits(newValue)); |
| 125 |
|
long newBits = doubleToRawLongBits(newValue); |
| 126 |
|
while (true) { |
| 127 |
|
long currentBits = value; |
| 128 |
< |
if (compareAndSet(currentBits, newBits)) |
| 128 |
> |
if (unsafe.compareAndSwapLong(this, valueOffset, |
| 129 |
> |
currentBits, newBits)) |
| 130 |
|
return longBitsToDouble(currentBits); |
| 131 |
|
} |
| 132 |
|
} |
| 172 |
|
while (true) { |
| 173 |
|
long currentBits = value; |
| 174 |
|
long nextBits = doubleToRawLongBits(longBitsToDouble(currentBits) + delta); |
| 175 |
< |
if (compareAndSet(currentBits, nextBits)) |
| 175 |
> |
if (unsafe.compareAndSwapLong(this, valueOffset, |
| 176 |
> |
currentBits, nextBits)) |
| 177 |
|
return longBitsToDouble(currentBits); |
| 178 |
|
} |
| 179 |
|
} |
| 233 |
|
return get(); |
| 234 |
|
} |
| 235 |
|
|
| 236 |
+ |
/** |
| 237 |
+ |
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
| 238 |
+ |
* Replace with a simple call to Unsafe.getUnsafe when integrating |
| 239 |
+ |
* into a jdk. |
| 240 |
+ |
* |
| 241 |
+ |
* @return a sun.misc.Unsafe |
| 242 |
+ |
*/ |
| 243 |
+ |
private static sun.misc.Unsafe getUnsafe() { |
| 244 |
+ |
try { |
| 245 |
+ |
return sun.misc.Unsafe.getUnsafe(); |
| 246 |
+ |
} catch (SecurityException se) { |
| 247 |
+ |
try { |
| 248 |
+ |
return java.security.AccessController.doPrivileged |
| 249 |
+ |
(new java.security |
| 250 |
+ |
.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
| 251 |
+ |
public sun.misc.Unsafe run() throws Exception { |
| 252 |
+ |
java.lang.reflect.Field f = sun.misc |
| 253 |
+ |
.Unsafe.class.getDeclaredField("theUnsafe"); |
| 254 |
+ |
f.setAccessible(true); |
| 255 |
+ |
return (sun.misc.Unsafe) f.get(null); |
| 256 |
+ |
}}); |
| 257 |
+ |
} catch (java.security.PrivilegedActionException e) { |
| 258 |
+ |
throw new RuntimeException("Could not initialize intrinsics", |
| 259 |
+ |
e.getCause()); |
| 260 |
+ |
} |
| 261 |
+ |
} |
| 262 |
+ |
} |
| 263 |
+ |
|
| 264 |
|
} |
