| 16 |
|
import java.util.WeakHashMap; |
| 17 |
|
|
| 18 |
|
/** |
| 19 |
< |
* Abstract base class for tasks that run within a {@link |
| 20 |
< |
* ForkJoinPool}. A ForkJoinTask is a thread-like entity that is much |
| 19 |
> |
* Abstract base class for tasks that run within a {@link ForkJoinPool}. |
| 20 |
> |
* A {@code ForkJoinTask} is a thread-like entity that is much |
| 21 |
|
* lighter weight than a normal thread. Huge numbers of tasks and |
| 22 |
|
* subtasks may be hosted by a small number of actual threads in a |
| 23 |
|
* ForkJoinPool, at the price of some usage limitations. |
| 24 |
|
* |
| 25 |
< |
* <p> A "main" ForkJoinTask begins execution when submitted to a |
| 26 |
< |
* {@link ForkJoinPool}. Once started, it will usually in turn start |
| 27 |
< |
* other subtasks. As indicated by the name of this class, many |
| 28 |
< |
* programs using ForkJoinTasks employ only methods {@code fork} and |
| 29 |
< |
* {@code join}, or derivatives such as {@code invokeAll}. However, |
| 30 |
< |
* this class also provides a number of other methods that can come |
| 31 |
< |
* into play in advanced usages, as well as extension mechanics that |
| 32 |
< |
* allow support of new forms of fork/join processing. |
| 25 |
> |
* <p>A "main" {@code ForkJoinTask} begins execution when submitted |
| 26 |
> |
* to a {@link ForkJoinPool}. Once started, it will usually in turn |
| 27 |
> |
* start other subtasks. As indicated by the name of this class, |
| 28 |
> |
* many programs using {@code ForkJoinTask} employ only methods |
| 29 |
> |
* {@link #fork} and {@link #join}, or derivatives such as {@link |
| 30 |
> |
* #invokeAll}. However, this class also provides a number of other |
| 31 |
> |
* methods that can come into play in advanced usages, as well as |
| 32 |
> |
* extension mechanics that allow support of new forms of fork/join |
| 33 |
> |
* processing. |
| 34 |
|
* |
| 35 |
< |
* <p>A ForkJoinTask is a lightweight form of {@link Future}. The |
| 36 |
< |
* efficiency of ForkJoinTasks stems from a set of restrictions (that |
| 37 |
< |
* are only partially statically enforceable) reflecting their |
| 38 |
< |
* intended use as computational tasks calculating pure functions or |
| 39 |
< |
* operating on purely isolated objects. The primary coordination |
| 40 |
< |
* mechanisms are {@link #fork}, that arranges asynchronous execution, |
| 41 |
< |
* and {@link #join}, that doesn't proceed until the task's result has |
| 42 |
< |
* been computed. Computations should avoid {@code synchronized} |
| 43 |
< |
* methods or blocks, and should minimize other blocking |
| 44 |
< |
* synchronization apart from joining other tasks or using |
| 45 |
< |
* synchronizers such as Phasers that are advertised to cooperate with |
| 46 |
< |
* fork/join scheduling. Tasks should also not perform blocking IO, |
| 47 |
< |
* and should ideally access variables that are completely independent |
| 48 |
< |
* of those accessed by other running tasks. Minor breaches of these |
| 49 |
< |
* restrictions, for example using shared output streams, may be |
| 50 |
< |
* tolerable in practice, but frequent use may result in poor |
| 51 |
< |
* performance, and the potential to indefinitely stall if the number |
| 52 |
< |
* of threads not waiting for IO or other external synchronization |
| 53 |
< |
* becomes exhausted. This usage restriction is in part enforced by |
| 54 |
< |
* not permitting checked exceptions such as {@code IOExceptions} |
| 55 |
< |
* to be thrown. However, computations may still encounter unchecked |
| 56 |
< |
* exceptions, that are rethrown to callers attempting join |
| 57 |
< |
* them. These exceptions may additionally include |
| 58 |
< |
* RejectedExecutionExceptions stemming from internal resource |
| 59 |
< |
* exhaustion such as failure to allocate internal task queues. |
| 35 |
> |
* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
| 36 |
> |
* The efficiency of {@code ForkJoinTask}s stems from a set of |
| 37 |
> |
* restrictions (that are only partially statically enforceable) |
| 38 |
> |
* reflecting their intended use as computational tasks calculating |
| 39 |
> |
* pure functions or operating on purely isolated objects. The |
| 40 |
> |
* primary coordination mechanisms are {@link #fork}, that arranges |
| 41 |
> |
* asynchronous execution, and {@link #join}, that doesn't proceed |
| 42 |
> |
* until the task's result has been computed. Computations should |
| 43 |
> |
* avoid {@code synchronized} methods or blocks, and should minimize |
| 44 |
> |
* other blocking synchronization apart from joining other tasks or |
| 45 |
> |
* using synchronizers such as Phasers that are advertised to |
| 46 |
> |
* cooperate with fork/join scheduling. Tasks should also not perform |
| 47 |
> |
* blocking IO, and should ideally access variables that are |
| 48 |
> |
* completely independent of those accessed by other running |
| 49 |
> |
* tasks. Minor breaches of these restrictions, for example using |
| 50 |
> |
* shared output streams, may be tolerable in practice, but frequent |
| 51 |
> |
* use may result in poor performance, and the potential to |
| 52 |
> |
* indefinitely stall if the number of threads not waiting for IO or |
| 53 |
> |
* other external synchronization becomes exhausted. This usage |
| 54 |
> |
* restriction is in part enforced by not permitting checked |
| 55 |
> |
* exceptions such as {@code IOExceptions} to be thrown. However, |
| 56 |
> |
* computations may still encounter unchecked exceptions, that are |
| 57 |
> |
* rethrown to callers attempting join them. These exceptions may |
| 58 |
> |
* additionally include RejectedExecutionExceptions stemming from |
| 59 |
> |
* internal resource exhaustion such as failure to allocate internal |
| 60 |
> |
* task queues. |
| 61 |
|
* |
| 62 |
|
* <p>The primary method for awaiting completion and extracting |
| 63 |
|
* results of a task is {@link #join}, but there are several variants: |
| 76 |
|
* performs the most common form of parallel invocation: forking a set |
| 77 |
|
* of tasks and joining them all. |
| 78 |
|
* |
| 79 |
< |
* <p> The ForkJoinTask class is not usually directly subclassed. |
| 79 |
> |
* <p>The ForkJoinTask class is not usually directly subclassed. |
| 80 |
|
* Instead, you subclass one of the abstract classes that support a |
| 81 |
< |
* particular style of fork/join processing. Normally, a concrete |
| 81 |
> |
* particular style of fork/join processing, typically {@link |
| 82 |
> |
* RecursiveAction} for computations that do not return results, or |
| 83 |
> |
* {@link RecursiveTask} for those that do. Normally, a concrete |
| 84 |
|
* ForkJoinTask subclass declares fields comprising its parameters, |
| 85 |
|
* established in a constructor, and then defines a {@code compute} |
| 86 |
|
* method that somehow uses the control methods supplied by this base |
| 110 |
|
* parallelism cannot improve throughput. If too small, then memory |
| 111 |
|
* and internal task maintenance overhead may overwhelm processing. |
| 112 |
|
* |
| 113 |
+ |
* <p>This class provides {@code adapt} methods for {@link |
| 114 |
+ |
* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that |
| 115 |
+ |
* may be of use when mixing execution of ForkJoinTasks with other |
| 116 |
+ |
* kinds of tasks. When all tasks are of this form, consider using a |
| 117 |
+ |
* pool in {@link ForkJoinPool#setAsyncMode}. |
| 118 |
+ |
* |
| 119 |
|
* <p>ForkJoinTasks are {@code Serializable}, which enables them |
| 120 |
|
* to be used in extensions such as remote execution frameworks. It is |
| 121 |
|
* in general sensible to serialize tasks only before or after, but |
| 257 |
|
synchronized (this) { |
| 258 |
|
try { |
| 259 |
|
while (status >= 0) { |
| 260 |
< |
long nt = nanos - System.nanoTime() - startTime; |
| 260 |
> |
long nt = nanos - (System.nanoTime() - startTime); |
| 261 |
|
if (nt <= 0) |
| 262 |
|
break; |
| 263 |
|
wait(nt / 1000000, (int) (nt % 1000000)); |
| 541 |
|
} |
| 542 |
|
|
| 543 |
|
/** |
| 544 |
< |
* Forks both tasks, returning when {@code isDone} holds for |
| 545 |
< |
* both of them or an exception is encountered. This method may be |
| 544 |
> |
* Forks the given tasks, returning when {@code isDone} holds for |
| 545 |
> |
* each task or an exception is encountered. This method may be |
| 546 |
|
* invoked only from within ForkJoinTask computations (as may be |
| 547 |
|
* determined using method {@link #inForkJoinPool}). Attempts to |
| 548 |
|
* invoke in other contexts result in exceptions or errors, |
| 549 |
|
* possibly including ClassCastException. |
| 550 |
|
* |
| 551 |
< |
* @param t1 one task |
| 552 |
< |
* @param t2 the other task |
| 553 |
< |
* @throws NullPointerException if t1 or t2 are null |
| 554 |
< |
* @throws RuntimeException or Error if either task did so |
| 551 |
> |
* @param t1 the first task |
| 552 |
> |
* @param t2 the second task |
| 553 |
> |
* @throws NullPointerException if any task is null |
| 554 |
> |
* @throws RuntimeException or Error if a task did so |
| 555 |
|
*/ |
| 556 |
|
public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) { |
| 557 |
|
t2.fork(); |
| 560 |
|
} |
| 561 |
|
|
| 562 |
|
/** |
| 563 |
< |
* Forks the given tasks, returning when {@code isDone} holds |
| 564 |
< |
* for all of them. If any task encounters an exception, others |
| 565 |
< |
* may be cancelled. This method may be invoked only from within |
| 563 |
> |
* Forks the given tasks, returning when {@code isDone} holds for |
| 564 |
> |
* each task or an exception is encountered. If any task |
| 565 |
> |
* encounters an exception, others may be, but are not guaranteed |
| 566 |
> |
* to be, cancelled. This method may be invoked only from within |
| 567 |
|
* ForkJoinTask computations (as may be determined using method |
| 568 |
|
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
| 569 |
|
* result in exceptions or errors, possibly including |
| 570 |
|
* ClassCastException. |
| 571 |
|
* |
| 572 |
< |
* @param tasks the array of tasks |
| 572 |
> |
* Overloadings of this method exist for the special cases |
| 573 |
> |
* of one to four arguments. |
| 574 |
> |
* |
| 575 |
> |
* @param tasks the tasks |
| 576 |
|
* @throws NullPointerException if tasks or any element are null |
| 577 |
|
* @throws RuntimeException or Error if any task did so |
| 578 |
|
*/ |
| 610 |
|
} |
| 611 |
|
|
| 612 |
|
/** |
| 613 |
< |
* Forks all tasks in the collection, returning when |
| 614 |
< |
* {@code isDone} holds for all of them. If any task |
| 615 |
< |
* encounters an exception, others may be cancelled. This method |
| 616 |
< |
* may be invoked only from within ForkJoinTask computations (as |
| 617 |
< |
* may be determined using method {@link |
| 618 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
| 619 |
< |
* in exceptions or errors, possibly including ClassCastException. |
| 613 |
> |
* Forks all tasks in the collection, returning when {@code |
| 614 |
> |
* isDone} holds for each task or an exception is encountered. If |
| 615 |
> |
* any task encounters an exception, others may be, but are not |
| 616 |
> |
* guaranteed to be, cancelled. This method may be invoked only |
| 617 |
> |
* from within ForkJoinTask computations (as may be determined |
| 618 |
> |
* using method {@link #inForkJoinPool}). Attempts to invoke in |
| 619 |
> |
* other contexts result in exceptions or errors, possibly |
| 620 |
> |
* including ClassCastException. |
| 621 |
|
* |
| 622 |
|
* @param tasks the collection of tasks |
| 623 |
|
* @return the tasks argument, to simplify usage |
| 700 |
|
* still ensure that these minimal properties hold. In particular, |
| 701 |
|
* the cancel method itself must not throw exceptions. |
| 702 |
|
* |
| 703 |
< |
* <p> This method is designed to be invoked by <em>other</em> |
| 703 |
> |
* <p>This method is designed to be invoked by <em>other</em> |
| 704 |
|
* tasks. To terminate the current task, you can just return or |
| 705 |
|
* throw an unchecked exception from its computation method, or |
| 706 |
|
* invoke {@link #completeExceptionally}. |
| 747 |
|
* {@code join} and related operations. This method may be used |
| 748 |
|
* to induce exceptions in asynchronous tasks, or to force |
| 749 |
|
* completion of tasks that would not otherwise complete. Its use |
| 750 |
< |
* in other situations is likely to be wrong. This method is |
| 750 |
> |
* in other situations is discouraged. This method is |
| 751 |
|
* overridable, but overridden versions must invoke {@code super} |
| 752 |
|
* implementation to maintain guarantees. |
| 753 |
|
* |
| 767 |
|
* operations. This method may be used to provide results for |
| 768 |
|
* asynchronous tasks, or to provide alternative handling for |
| 769 |
|
* tasks that would not otherwise complete normally. Its use in |
| 770 |
< |
* other situations is likely to be wrong. This method is |
| 770 |
> |
* other situations is discouraged. This method is |
| 771 |
|
* overridable, but overridden versions must invoke {@code super} |
| 772 |
|
* implementation to maintain guarantees. |
| 773 |
|
* |
| 792 |
|
|
| 793 |
|
public final V get(long timeout, TimeUnit unit) |
| 794 |
|
throws InterruptedException, ExecutionException, TimeoutException { |
| 795 |
+ |
long nanos = unit.toNanos(timeout); |
| 796 |
|
ForkJoinWorkerThread w = getWorker(); |
| 797 |
|
if (w == null || status < 0 || !w.unpushTask(this) || !tryQuietlyInvoke()) |
| 798 |
< |
awaitDone(w, unit.toNanos(timeout)); |
| 798 |
> |
awaitDone(w, nanos); |
| 799 |
|
return reportTimedFutureResult(); |
| 800 |
|
} |
| 801 |
|
|
| 867 |
|
* Possibly executes tasks until the pool hosting the current task |
| 868 |
|
* {@link ForkJoinPool#isQuiescent}. This method may be of use in |
| 869 |
|
* designs in which many tasks are forked, but none are explicitly |
| 870 |
< |
* joined, instead executing them until all are processed. |
| 870 |
> |
* joined, instead executing them until all are processed. This |
| 871 |
> |
* method may be invoked only from within ForkJoinTask |
| 872 |
> |
* computations (as may be determined using method {@link |
| 873 |
> |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
| 874 |
> |
* in exceptions or errors, possibly including ClassCastException. |
| 875 |
|
*/ |
| 876 |
|
public static void helpQuiesce() { |
| 877 |
|
((ForkJoinWorkerThread) Thread.currentThread()) |
| 885 |
|
* never been forked, or has been forked, then completed and all |
| 886 |
|
* outstanding joins of this task have also completed. Effects |
| 887 |
|
* under any other usage conditions are not guaranteed, and are |
| 888 |
< |
* almost surely wrong. This method may be useful when executing |
| 888 |
> |
* discouraged. This method may be useful when executing |
| 889 |
|
* pre-constructed trees of subtasks in loops. |
| 890 |
|
*/ |
| 891 |
|
public void reinitialize() { |
| 898 |
|
* Returns the pool hosting the current task execution, or null |
| 899 |
|
* if this task is executing outside of any ForkJoinPool. |
| 900 |
|
* |
| 901 |
+ |
* @see #inForkJoinPool |
| 902 |
|
* @return the pool, or {@code null} if none |
| 903 |
|
*/ |
| 904 |
|
public static ForkJoinPool getPool() { |
| 941 |
|
* Returns an estimate of the number of tasks that have been |
| 942 |
|
* forked by the current worker thread but not yet executed. This |
| 943 |
|
* value may be useful for heuristic decisions about whether to |
| 944 |
< |
* fork other tasks. |
| 945 |
< |
* |
| 944 |
> |
* fork other tasks. This method may be invoked only from within |
| 945 |
> |
* ForkJoinTask computations (as may be determined using method |
| 946 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
| 947 |
> |
* result in exceptions or errors, possibly including |
| 948 |
> |
* ClassCastException. |
| 949 |
|
* @return the number of tasks |
| 950 |
|
*/ |
| 951 |
|
public static int getQueuedTaskCount() { |
| 961 |
|
* usages of ForkJoinTasks, at steady state, each worker should |
| 962 |
|
* aim to maintain a small constant surplus (for example, 3) of |
| 963 |
|
* tasks, and to process computations locally if this threshold is |
| 964 |
< |
* exceeded. |
| 965 |
< |
* |
| 964 |
> |
* exceeded. This method may be invoked only from within |
| 965 |
> |
* ForkJoinTask computations (as may be determined using method |
| 966 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
| 967 |
> |
* result in exceptions or errors, possibly including |
| 968 |
> |
* ClassCastException. * |
| 969 |
|
* @return the surplus number of tasks, which may be negative |
| 970 |
|
*/ |
| 971 |
|
public static int getSurplusQueuedTaskCount() { |
| 1010 |
|
protected abstract boolean exec(); |
| 1011 |
|
|
| 1012 |
|
/** |
| 1013 |
< |
* Returns, but does not unschedule or execute, the task queued by |
| 1014 |
< |
* the current thread but not yet executed, if one is |
| 1013 |
> |
* Returns, but does not unschedule or execute, a task queued by |
| 1014 |
> |
* the current thread but not yet executed, if one is immediately |
| 1015 |
|
* available. There is no guarantee that this task will actually |
| 1016 |
< |
* be polled or executed next. This method is designed primarily |
| 1017 |
< |
* to support extensions, and is unlikely to be useful otherwise. |
| 1018 |
< |
* This method may be invoked only from within ForkJoinTask |
| 1019 |
< |
* computations (as may be determined using method {@link |
| 1020 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
| 1021 |
< |
* in exceptions or errors, possibly including ClassCastException. |
| 1016 |
> |
* be polled or executed next. Conversely, this method may return |
| 1017 |
> |
* null even if a task exists but cannot be accessed without |
| 1018 |
> |
* contention with other threads. This method is designed |
| 1019 |
> |
* primarily to support extensions, and is unlikely to be useful |
| 1020 |
> |
* otherwise. This method may be invoked only from within |
| 1021 |
> |
* ForkJoinTask computations (as may be determined using method |
| 1022 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
| 1023 |
> |
* result in exceptions or errors, possibly including |
| 1024 |
> |
* ClassCastException. |
| 1025 |
|
* |
| 1026 |
|
* @return the next task, or {@code null} if none are available |
| 1027 |
|
*/ |
| 1068 |
|
.pollTask(); |
| 1069 |
|
} |
| 1070 |
|
|
| 1071 |
< |
// adaptors |
| 1071 |
> |
/** |
| 1072 |
> |
* Adaptor for Runnables. This implements RunnableFuture |
| 1073 |
> |
* to be compliant with AbstractExecutorService constraints |
| 1074 |
> |
* when used in ForkJoinPool. |
| 1075 |
> |
*/ |
| 1076 |
> |
static final class AdaptedRunnable<T> extends ForkJoinTask<T> |
| 1077 |
> |
implements RunnableFuture<T> { |
| 1078 |
> |
final Runnable runnable; |
| 1079 |
> |
final T resultOnCompletion; |
| 1080 |
> |
T result; |
| 1081 |
> |
AdaptedRunnable(Runnable runnable, T result) { |
| 1082 |
> |
if (runnable == null) throw new NullPointerException(); |
| 1083 |
> |
this.runnable = runnable; |
| 1084 |
> |
this.resultOnCompletion = result; |
| 1085 |
> |
} |
| 1086 |
> |
public T getRawResult() { return result; } |
| 1087 |
> |
public void setRawResult(T v) { result = v; } |
| 1088 |
> |
public boolean exec() { |
| 1089 |
> |
runnable.run(); |
| 1090 |
> |
result = resultOnCompletion; |
| 1091 |
> |
return true; |
| 1092 |
> |
} |
| 1093 |
> |
public void run() { invoke(); } |
| 1094 |
> |
private static final long serialVersionUID = 5232453952276885070L; |
| 1095 |
> |
} |
| 1096 |
> |
|
| 1097 |
> |
/** |
| 1098 |
> |
* Adaptor for Callables |
| 1099 |
> |
*/ |
| 1100 |
> |
static final class AdaptedCallable<T> extends ForkJoinTask<T> |
| 1101 |
> |
implements RunnableFuture<T> { |
| 1102 |
> |
final Callable<? extends T> callable; |
| 1103 |
> |
T result; |
| 1104 |
> |
AdaptedCallable(Callable<? extends T> callable) { |
| 1105 |
> |
if (callable == null) throw new NullPointerException(); |
| 1106 |
> |
this.callable = callable; |
| 1107 |
> |
} |
| 1108 |
> |
public T getRawResult() { return result; } |
| 1109 |
> |
public void setRawResult(T v) { result = v; } |
| 1110 |
> |
public boolean exec() { |
| 1111 |
> |
try { |
| 1112 |
> |
result = callable.call(); |
| 1113 |
> |
return true; |
| 1114 |
> |
} catch (Error err) { |
| 1115 |
> |
throw err; |
| 1116 |
> |
} catch (RuntimeException rex) { |
| 1117 |
> |
throw rex; |
| 1118 |
> |
} catch (Exception ex) { |
| 1119 |
> |
throw new RuntimeException(ex); |
| 1120 |
> |
} |
| 1121 |
> |
} |
| 1122 |
> |
public void run() { invoke(); } |
| 1123 |
> |
private static final long serialVersionUID = 2838392045355241008L; |
| 1124 |
> |
} |
| 1125 |
|
|
| 1126 |
|
/** |
| 1127 |
|
* Returns a new ForkJoinTask that performs the {@code run} |
| 1131 |
|
* @param runnable the runnable action |
| 1132 |
|
* @return the task |
| 1133 |
|
*/ |
| 1134 |
< |
public static ForkJoinTask<Void> adapt(Runnable runnable) { |
| 1135 |
< |
return new ForkJoinPool.AdaptedRunnable<Void>(runnable, null); |
| 1134 |
> |
public static ForkJoinTask<?> adapt(Runnable runnable) { |
| 1135 |
> |
return new AdaptedRunnable<Void>(runnable, null); |
| 1136 |
|
} |
| 1137 |
|
|
| 1138 |
|
/** |
| 1145 |
|
* @return the task |
| 1146 |
|
*/ |
| 1147 |
|
public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) { |
| 1148 |
< |
return new ForkJoinPool.AdaptedRunnable<T>(runnable, result); |
| 1148 |
> |
return new AdaptedRunnable<T>(runnable, result); |
| 1149 |
|
} |
| 1150 |
|
|
| 1151 |
|
/** |
| 1157 |
|
* @param callable the callable action |
| 1158 |
|
* @return the task |
| 1159 |
|
*/ |
| 1160 |
< |
public static <T> ForkJoinTask<T> adapt(Callable<T> callable) { |
| 1161 |
< |
return new ForkJoinPool.AdaptedCallable<T>(callable); |
| 1160 |
> |
public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { |
| 1161 |
> |
return new AdaptedCallable<T>(callable); |
| 1162 |
|
} |
| 1163 |
|
|
| 1164 |
|
// Serialization support |
