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root/jsr166/jsr166/src/jsr166y/ForkJoinPool.java

Comparing jsr166/src/jsr166y/ForkJoinPool.java (file contents):
Revision 1.26 by jsr166, Sun Jul 26 13:34:25 2009 UTC vs.
Revision 1.30 by dl, Wed Jul 29 12:05:55 2009 UTC

#	Line 20 | Line 20 | import java.util.concurrent.atomic.Atomi
20		import java.util.concurrent.atomic.AtomicLong;
21
22		/**
23	<	* An {@link ExecutorService} for running {@link ForkJoinTask}s.  A
24	<	* ForkJoinPool provides the entry point for submissions from
23	>	* An {@link ExecutorService} for running {@link ForkJoinTask}s.
24	>	* A ForkJoinPool provides the entry point for submissions from
25		* non-ForkJoinTasks, as well as management and monitoring operations.
26		* Normally a single ForkJoinPool is used for a large number of
27		* submitted tasks. Otherwise, use would not usually outweigh the
#	Line 34 | Line 34 | import java.util.concurrent.atomic.Atomi
34		* (eventually blocking if none exist). This makes them efficient when
35		* most tasks spawn other subtasks (as do most ForkJoinTasks), as well
36		* as the mixed execution of some plain Runnable- or Callable- based
37	<	* activities along with ForkJoinTasks. When setting
38	<	* {@code setAsyncMode}, a ForkJoinPools may also be appropriate for
39	<	* use with fine-grained tasks that are never joined. Otherwise, other
40	<	* ExecutorService implementations are typically more appropriate
41	<	* choices.
37	>	* activities along with ForkJoinTasks. When setting {@linkplain
38	>	* #setAsyncMode async mode}, a ForkJoinPool may also be appropriate
39	>	* for use with fine-grained tasks that are never joined. Otherwise,
40	>	* other ExecutorService implementations are typically more
41	>	* appropriate choices.
42		*
43		* <p>A ForkJoinPool may be constructed with a given parallelism level
44		* (target pool size), which it attempts to maintain by dynamically
45		* adding, suspending, or resuming threads, even if some tasks are
46		* waiting to join others. However, no such adjustments are performed
47		* in the face of blocked IO or other unmanaged synchronization. The
48	<	* nested {@code ManagedBlocker} interface enables extension of
48	>	* nested {@link ManagedBlocker} interface enables extension of
49		* the kinds of synchronization accommodated.  The target parallelism
50	<	* level may also be changed dynamically ({@code setParallelism})
50	>	* level may also be changed dynamically ({@link #setParallelism})
51		* and thread construction can be limited using methods
52	<	* {@code setMaximumPoolSize} and/or
53	<	* {@code setMaintainsParallelism}.
52	>	* {@link #setMaximumPoolSize} and/or
53	>	* {@link #setMaintainsParallelism}.
54		*
55		* <p>In addition to execution and lifecycle control methods, this
56		* class provides status check methods (for example
57	<	* {@code getStealCount}) that are intended to aid in developing,
57	>	* {@link #getStealCount}) that are intended to aid in developing,
58		* tuning, and monitoring fork/join applications. Also, method
59	<	* {@code toString} returns indications of pool state in a
59	>	* {@link #toString} returns indications of pool state in a
60		* convenient form for informal monitoring.
61		*
62		* <p><b>Implementation notes</b>: This implementation restricts the
#	Line 311 | Line 311 | public class ForkJoinPool extends Abstra
311		}
312
313		/**
314	<	* Returns true if argument represents zero active count and
315	<	* nonzero runstate, which is the triggering condition for
314	>	* Returns {@code true} if argument represents zero active count
315	>	* and nonzero runstate, which is the triggering condition for
316		* terminating on shutdown.
317		*/
318		private static boolean canTerminateOnShutdown(int c) {
#	Line 720 | Line 720 | public class ForkJoinPool extends Abstra
720		* Returns the handler for internal worker threads that terminate
721		* due to unrecoverable errors encountered while executing tasks.
722		*
723	<	* @return the handler, or null if none
723	>	* @return the handler, or {@code null} if none
724		*/
725		public Thread.UncaughtExceptionHandler getUncaughtExceptionHandler() {
726		Thread.UncaughtExceptionHandler h;
#	Line 741 | Line 741 | public class ForkJoinPool extends Abstra
741		* as handler.
742		*
743		* @param h the new handler
744	<	* @return the old handler, or null if none
744	>	* @return the old handler, or {@code null} if none
745		* @throws SecurityException if a security manager exists and
746		*         the caller is not permitted to modify threads
747		*         because it does not hold {@link
#	Line 815 | Line 815 | public class ForkJoinPool extends Abstra
815		/**
816		* Returns the number of worker threads that have started but not
817		* yet terminated.  This result returned by this method may differ
818	<	* from {@code getParallelism} when threads are created to
818	>	* from {@link #getParallelism} when threads are created to
819		* maintain parallelism when others are cooperatively blocked.
820		*
821		* @return the number of worker threads
#	Line 851 | Line 851 | public class ForkJoinPool extends Abstra
851
852
853		/**
854	<	* Returns true if this pool dynamically maintains its target
855	<	* parallelism level. If false, new threads are added only to
856	<	* avoid possible starvation.
857	<	* This setting is by default true.
854	>	* Returns {@code true} if this pool dynamically maintains its
855	>	* target parallelism level. If false, new threads are added only
856	>	* to avoid possible starvation.  This setting is by default true.
857		*
858	<	* @return true if maintains parallelism
858	>	* @return {@code true} if maintains parallelism
859		*/
860		public boolean getMaintainsParallelism() {
861		return maintainsParallelism;
#	Line 867 | Line 866 | public class ForkJoinPool extends Abstra
866		* parallelism level. If false, new threads are added only to
867		* avoid possible starvation.
868		*
869	<	* @param enable true to maintains parallelism
869	>	* @param enable {@code true} to maintain parallelism
870		*/
871		public void setMaintainsParallelism(boolean enable) {
872		maintainsParallelism = enable;
#	Line 878 | Line 877 | public class ForkJoinPool extends Abstra
877		* tasks that are never joined. This mode may be more appropriate
878		* than default locally stack-based mode in applications in which
879		* worker threads only process asynchronous tasks.  This method is
880	<	* designed to be invoked only when pool is quiescent, and
880	>	* designed to be invoked only when the pool is quiescent, and
881		* typically only before any tasks are submitted. The effects of
882		* invocations at other times may be unpredictable.
883		*
884	<	* @param async if true, use locally FIFO scheduling
884	>	* @param async if {@code true}, use locally FIFO scheduling
885		* @return the previous mode
886	+	* @see #getAsyncMode
887		*/
888		public boolean setAsyncMode(boolean async) {
889		boolean oldMode = locallyFifo;
#	Line 900 | Line 900 | public class ForkJoinPool extends Abstra
900		}
901
902		/**
903	<	* Returns true if this pool uses local first-in-first-out
903	>	* Returns {@code true} if this pool uses local first-in-first-out
904		* scheduling mode for forked tasks that are never joined.
905		*
906	<	* @return true if this pool uses async mode
906	>	* @return {@code true} if this pool uses async mode
907	>	* @see #setAsyncMode
908		*/
909		public boolean getAsyncMode() {
910		return locallyFifo;
#	Line 944 | Line 945 | public class ForkJoinPool extends Abstra
945		}
946
947		/**
948	<	* Returns true if all worker threads are currently idle. An idle
949	<	* worker is one that cannot obtain a task to execute because none
950	<	* are available to steal from other threads, and there are no
951	<	* pending submissions to the pool. This method is conservative;
952	<	* it might not return true immediately upon idleness of all
953	<	* threads, but will eventually become true if threads remain
954	<	* inactive.
948	>	* Returns {@code true} if all worker threads are currently idle.
949	>	* An idle worker is one that cannot obtain a task to execute
950	>	* because none are available to steal from other threads, and
951	>	* there are no pending submissions to the pool. This method is
952	>	* conservative; it might not return {@code true} immediately upon
953	>	* idleness of all threads, but will eventually become true if
954	>	* threads remain inactive.
955		*
956	<	* @return true if all threads are currently idle
956	>	* @return {@code true} if all threads are currently idle
957		*/
958		public boolean isQuiescent() {
959		return activeCountOf(runControl) == 0;
#	Line 1018 | Line 1019 | public class ForkJoinPool extends Abstra
1019		}
1020
1021		/**
1022	<	* Returns true if there are any tasks submitted to this pool
1023	<	* that have not yet begun executing.
1022	>	* Returns {@code true} if there are any tasks submitted to this
1023	>	* pool that have not yet begun executing.
1024		*
1025		* @return {@code true} if there are any queued submissions
1026		*/
#	Line 1032 | Line 1033 | public class ForkJoinPool extends Abstra
1033		* available.  This method may be useful in extensions to this
1034		* class that re-assign work in systems with multiple pools.
1035		*
1036	<	* @return the next submission, or null if none
1036	>	* @return the next submission, or {@code null} if none
1037		*/
1038		protected ForkJoinTask<?> pollSubmission() {
1039		return submissionQueue.poll();
#	Line 1055 | Line 1056 | public class ForkJoinPool extends Abstra
1056		* @param c the collection to transfer elements into
1057		* @return the number of elements transferred
1058		*/
1059	<	protected int drainTasksTo(Collection<ForkJoinTask<?>> c) {
1059	>	protected int drainTasksTo(Collection<? super ForkJoinTask<?>> c) {
1060		int n = submissionQueue.drainTo(c);
1061		ForkJoinWorkerThread[] ws = workers;
1062		if (ws != null) {
#	Line 1132 | Line 1133 | public class ForkJoinPool extends Abstra
1133		* method may or may not be rejected. Unlike some other executors,
1134		* this method cancels rather than collects non-executed tasks
1135		* upon termination, so always returns an empty list. However, you
1136	<	* can use method {@code drainTasksTo} before invoking this
1136	>	* can use method {@link #drainTasksTo} before invoking this
1137		* method to transfer unexecuted tasks to another collection.
1138		*
1139		* @return an empty list
#	Line 1492 | Line 1493 | public class ForkJoinPool extends Abstra
1493		}
1494
1495		/**
1496	<	* Returns true if worker waiting on sync can proceed:
1496	>	* Returns {@code true} if worker waiting on sync can proceed:
1497		*  - on signal (thread == null)
1498		*  - on event count advance (winning race to notify vs signaller)
1499		*  - on interrupt
#	Line 1500 | Line 1501 | public class ForkJoinPool extends Abstra
1501		* If node was not signalled and event count not advanced on exit,
1502		* then we also help advance event count.
1503		*
1504	<	* @return true if node can be released
1504	>	* @return {@code true} if node can be released
1505		*/
1506		final boolean syncIsReleasable(WaitQueueNode node) {
1507		long prev = node.count;
#	Line 1519 | Line 1520 | public class ForkJoinPool extends Abstra
1520		}
1521
1522		/**
1523	<	* Returns true if a new sync event occurred since last call to
1524	<	* sync or this method, if so, updating caller's count.
1523	>	* Returns {@code true} if a new sync event occurred since last
1524	>	* call to sync or this method, if so, updating caller's count.
1525		*/
1526		final boolean hasNewSyncEvent(ForkJoinWorkerThread w) {
1527		long lc = w.lastEventCount;
#	Line 1604 | Line 1605 | public class ForkJoinPool extends Abstra
1605		}
1606
1607		/**
1608	<	* Returns true if a spare thread appears to be needed.  If
1609	<	* maintaining parallelism, returns true when the deficit in
1608	>	* Returns {@code true} if a spare thread appears to be needed.
1609	>	* If maintaining parallelism, returns true when the deficit in
1610		* running threads is more than the surplus of total threads, and
1611		* there is apparently some work to do.  This self-limiting rule
1612		* means that the more threads that have already been added, the
#	Line 1774 | Line 1775 | public class ForkJoinPool extends Abstra
1775		/**
1776		* Interface for extending managed parallelism for tasks running
1777		* in ForkJoinPools. A ManagedBlocker provides two methods.
1778	<	* Method {@code isReleasable} must return true if blocking is not
1779	<	* necessary. Method {@code block} blocks the current thread if
1780	<	* necessary (perhaps internally invoking {@code isReleasable}
1781	<	* before actually blocking.).
1778	>	* Method {@code isReleasable} must return {@code true} if
1779	>	* blocking is not necessary. Method {@code block} blocks the
1780	>	* current thread if necessary (perhaps internally invoking
1781	>	* {@code isReleasable} before actually blocking.).
1782		*
1783		* <p>For example, here is a ManagedBlocker based on a
1784		* ReentrantLock:
#	Line 1801 | Line 1802 | public class ForkJoinPool extends Abstra
1802		* Possibly blocks the current thread, for example waiting for
1803		* a lock or condition.
1804		*
1805	<	* @return true if no additional blocking is necessary (i.e.,
1806	<	* if isReleasable would return true)
1805	>	* @return {@code true} if no additional blocking is necessary
1806	>	* (i.e., if isReleasable would return true)
1807		* @throws InterruptedException if interrupted while waiting
1808		* (the method is not required to do so, but is allowed to)
1809		*/
1810		boolean block() throws InterruptedException;
1811
1812		/**
1813	<	* Returns true if blocking is unnecessary.
1813	>	* Returns {@code true} if blocking is unnecessary.
1814		*/
1815		boolean isReleasable();
1816		}
#	Line 1819 | Line 1820 | public class ForkJoinPool extends Abstra
1820		* is a ForkJoinWorkerThread, this method possibly arranges for a
1821		* spare thread to be activated if necessary to ensure parallelism
1822		* while the current thread is blocked.  If
1823	<	* {@code maintainParallelism} is true and the pool supports
1823	>	* {@code maintainParallelism} is {@code true} and the pool supports
1824		* it ({@link #getMaintainsParallelism}), this method attempts to
1825		* maintain the pool's nominal parallelism. Otherwise it activates
1826		* a thread only if necessary to avoid complete starvation. This
#	Line 1837 | Line 1838 | public class ForkJoinPool extends Abstra
1838		* be expanded to ensure parallelism, and later adjusted.
1839		*
1840		* @param blocker the blocker
1841	<	* @param maintainParallelism if true and supported by this pool,
1842	<	* attempt to maintain the pool's nominal parallelism; otherwise
1843	<	* activate a thread only if necessary to avoid complete
1844	<	* starvation.
1841	>	* @param maintainParallelism if {@code true} and supported by
1842	>	* this pool, attempt to maintain the pool's nominal parallelism;
1843	>	* otherwise activate a thread only if necessary to avoid
1844	>	* complete starvation.
1845		* @throws InterruptedException if blocker.block did so
1846		*/
1847		public static void managedBlock(ManagedBlocker blocker,
#	Line 1876 | Line 1877 | public class ForkJoinPool extends Abstra
1877		return new AdaptedCallable<T>(callable);
1878		}
1879
1880	<
1880	<	// Unsafe mechanics for jsr166y 3rd party package.
1881	<	private static sun.misc.Unsafe getUnsafe() {
1882	<	try {
1883	<	return sun.misc.Unsafe.getUnsafe();
1884	<	} catch (SecurityException se) {
1885	<	try {
1886	<	return java.security.AccessController.doPrivileged
1887	<	(new java.security.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1888	<	public sun.misc.Unsafe run() throws Exception {
1889	<	return getUnsafeByReflection();
1890	<	}});
1891	<	} catch (java.security.PrivilegedActionException e) {
1892	<	throw new RuntimeException("Could not initialize intrinsics",
1893	<	e.getCause());
1894	<	}
1895	<	}
1896	<	}
1897	<
1898	<	private static sun.misc.Unsafe getUnsafeByReflection()
1899	<	throws NoSuchFieldException, IllegalAccessException {
1900	<	java.lang.reflect.Field f =
1901	<	sun.misc.Unsafe.class.getDeclaredField("theUnsafe");
1902	<	f.setAccessible(true);
1903	<	return (sun.misc.Unsafe) f.get(null);
1904	<	}
1905	<
1906	<	private static long fieldOffset(String fieldName, Class<?> klazz) {
1907	<	try {
1908	<	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(fieldName));
1909	<	} catch (NoSuchFieldException e) {
1910	<	// Convert Exception to Error
1911	<	NoSuchFieldError error = new NoSuchFieldError(fieldName);
1912	<	error.initCause(e);
1913	<	throw error;
1914	<	}
1915	<	}
1880	>	// Unsafe mechanics
1881
1882		private static final sun.misc.Unsafe UNSAFE = getUnsafe();
1883		private static final long eventCountOffset =
1884	<	fieldOffset("eventCount", ForkJoinPool.class);
1884	>	objectFieldOffset("eventCount", ForkJoinPool.class);
1885		private static final long workerCountsOffset =
1886	<	fieldOffset("workerCounts", ForkJoinPool.class);
1886	>	objectFieldOffset("workerCounts", ForkJoinPool.class);
1887		private static final long runControlOffset =
1888	<	fieldOffset("runControl", ForkJoinPool.class);
1888	>	objectFieldOffset("runControl", ForkJoinPool.class);
1889		private static final long syncStackOffset =
1890	<	fieldOffset("syncStack",ForkJoinPool.class);
1890	>	objectFieldOffset("syncStack",ForkJoinPool.class);
1891		private static final long spareStackOffset =
1892	<	fieldOffset("spareStack", ForkJoinPool.class);
1892	>	objectFieldOffset("spareStack", ForkJoinPool.class);
1893
1894		private boolean casEventCount(long cmp, long val) {
1895		return UNSAFE.compareAndSwapLong(this, eventCountOffset, cmp, val);
#	Line 1941 | Line 1906 | public class ForkJoinPool extends Abstra
1906		private boolean casBarrierStack(WaitQueueNode cmp, WaitQueueNode val) {
1907		return UNSAFE.compareAndSwapObject(this, syncStackOffset, cmp, val);
1908		}
1909	+
1910	+	private static long objectFieldOffset(String field, Class<?> klazz) {
1911	+	try {
1912	+	return UNSAFE.objectFieldOffset(klazz.getDeclaredField(field));
1913	+	} catch (NoSuchFieldException e) {
1914	+	// Convert Exception to corresponding Error
1915	+	NoSuchFieldError error = new NoSuchFieldError(field);
1916	+	error.initCause(e);
1917	+	throw error;
1918	+	}
1919	+	}
1920	+
1921	+	/**
1922	+	* Returns a sun.misc.Unsafe.  Suitable for use in a 3rd party package.
1923	+	* Replace with a simple call to Unsafe.getUnsafe when integrating
1924	+	* into a jdk.
1925	+	*
1926	+	* @return a sun.misc.Unsafe
1927	+	*/
1928	+	private static sun.misc.Unsafe getUnsafe() {
1929	+	try {
1930	+	return sun.misc.Unsafe.getUnsafe();
1931	+	} catch (SecurityException se) {
1932	+	try {
1933	+	return java.security.AccessController.doPrivileged
1934	+	(new java.security
1935	+	.PrivilegedExceptionAction<sun.misc.Unsafe>() {
1936	+	public sun.misc.Unsafe run() throws Exception {
1937	+	java.lang.reflect.Field f = sun.misc
1938	+	.Unsafe.class.getDeclaredField("theUnsafe");
1939	+	f.setAccessible(true);
1940	+	return (sun.misc.Unsafe) f.get(null);
1941	+	}});
1942	+	} catch (java.security.PrivilegedActionException e) {
1943	+	throw new RuntimeException("Could not initialize intrinsics",
1944	+	e.getCause());
1945	+	}
1946	+	}
1947	+	}
1948		}

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