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package jsr166e; |
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import java.util.Random; |
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import java.util.concurrent.atomic.AtomicInteger; |
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import java.util.concurrent.atomic.AtomicLong; |
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/** |
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* A package-local class holding common representation and mechanics |
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* for classes supporting dynamic striping on 64bit values. The class |
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* extends Number so that concrete subclasses can publicly do so. |
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* extends Number so that concrete subclasses must publicly do so. |
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*/ |
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abstract class Striped64 extends Number { |
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/* |
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* |
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* A single spinlock ("busy") is used for initializing and |
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* resizing the table, as well as populating slots with new Cells. |
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* There is no need for a blocking lock: When the lock is not |
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* There is no need for a blocking lock; when the lock is not |
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* available, threads try other slots (or the base). During these |
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* retries, there is increased contention and reduced locality, |
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* which is still better than alternatives. |
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*/ |
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/** |
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* Padded variant of AtomicLong supporting only raw accesses plus |
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* CAS The value field is placed between pads, hoping that the JVM |
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* doesn't reorder them. |
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* Padded variant of AtomicLong supporting only raw accesses plus CAS. |
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* The value field is placed between pads, hoping that the JVM doesn't |
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* reorder them. |
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* |
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* JVM intrinsics note: It would be possible to use a release-only |
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* form of CAS here, if it were provided. |
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} |
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/** |
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* Holder for the thread-local hash code. The code is initially |
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* random, but may be set to a different value upon collisions. |
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* ThreadLocal holding a single-slot int array holding hash code. |
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* Unlike the JDK8 version of this class, we use a suboptimal |
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* int[] representation to avoid introducing a new type that can |
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* impede class-unloading when ThreadLocals are not removed. |
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*/ |
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static final class HashCode { |
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static final Random rng = new Random(); |
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int code; |
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HashCode() { |
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int h = rng.nextInt(); // Avoid zero to allow xorShift rehash |
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code = (h == 0) ? 1 : h; |
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} |
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} |
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/** |
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* The corresponding ThreadLocal class |
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*/ |
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static final class ThreadHashCode extends ThreadLocal<HashCode> { |
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public HashCode initialValue() { return new HashCode(); } |
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} |
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static final ThreadLocal<int[]> threadHashCode = new ThreadLocal<int[]>(); |
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/** |
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* Static per-thread hash codes. Shared across all instances to |
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* reduce ThreadLocal pollution and because adjustments due to |
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* collisions in one table are likely to be appropriate for |
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* others. |
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* Generator of new random hash codes |
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*/ |
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static final ThreadHashCode threadHashCode = new ThreadHashCode(); |
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static final Random rng = new Random(); |
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/** Nomber of CPUS, to place bound on table size */ |
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/** Number of CPUS, to place bound on table size */ |
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static final int NCPU = Runtime.getRuntime().availableProcessors(); |
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/** |
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/** |
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* Base value, used mainly when there is no contention, but also as |
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* a fallback during table initializion races. Updated via CAS. |
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* a fallback during table initialization races. Updated via CAS. |
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*/ |
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transient volatile long base; |
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} |
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/** |
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* CAS the base field |
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* CASes the base field. |
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*/ |
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final boolean casBase(long cmp, long val) { |
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return UNSAFE.compareAndSwapLong(this, baseOffset, cmp, val); |
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} |
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/** |
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* CAS the busy field from 0 to 1 to acquire lock. |
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* CASes the busy field from 0 to 1 to acquire lock. |
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*/ |
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final boolean casBusy() { |
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return UNSAFE.compareAndSwapInt(this, busyOffset, 0, 1); |
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* @param hc the hash code holder |
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* @param wasUncontended false if CAS failed before call |
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*/ |
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final void retryUpdate(long x, HashCode hc, boolean wasUncontended) { |
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int h = hc.code; |
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final void retryUpdate(long x, int[] hc, boolean wasUncontended) { |
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int h; |
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if (hc == null) { |
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threadHashCode.set(hc = new int[1]); // Initialize randomly |
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int r = rng.nextInt(); // Avoid zero to allow xorShift rehash |
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h = hc[0] = (r == 0) ? 1 : r; |
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} |
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else |
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h = hc[0]; |
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boolean collide = false; // True if last slot nonempty |
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for (;;) { |
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Cell[] as; Cell a; int n; long v; |
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h ^= h << 13; // Rehash |
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h ^= h >>> 17; |
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h ^= h << 5; |
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hc[0] = h; // Record index for next time |
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} |
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else if (busy == 0 && cells == as && casBusy()) { |
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boolean init = false; |
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else if (casBase(v = base, fn(v, x))) |
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break; // Fall back on using base |
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} |
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hc.code = h; // Record index for next time |
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} |
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/** |
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* Set base and all cells to the given value |
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* Sets base and all cells to the given value. |
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*/ |
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final void internalReset(long initialValue) { |
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Cell[] as = cells; |
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private static sun.misc.Unsafe getUnsafe() { |
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try { |
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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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} catch (SecurityException tryReflectionInstead) {} |
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try { |
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return java.security.AccessController.doPrivileged |
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(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() { |
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public sun.misc.Unsafe run() throws Exception { |
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Class<sun.misc.Unsafe> k = sun.misc.Unsafe.class; |
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for (java.lang.reflect.Field f : k.getDeclaredFields()) { |
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f.setAccessible(true); |
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Object x = f.get(null); |
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if (k.isInstance(x)) |
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return k.cast(x); |
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} |
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throw new NoSuchFieldError("the Unsafe"); |
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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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} |
