12 |
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import java.util.Collection; |
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import java.util.Collections; |
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import java.util.List; |
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import java.util.RandomAccess; |
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import java.util.Map; |
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import java.util.WeakHashMap; |
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|
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* subtasks may be hosted by a small number of actual threads in a |
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* ForkJoinPool, at the price of some usage limitations. |
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* |
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* <p> A "main" ForkJoinTask begins execution when submitted to a |
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* {@link ForkJoinPool}. Once started, it will usually in turn start |
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* other subtasks. As indicated by the name of this class, many |
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* programs using ForkJoinTasks employ only methods {@code fork} and |
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* {@code join}, or derivatives such as {@code invokeAll}. However, |
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* this class also provides a number of other methods that can come |
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* into play in advanced usages, as well as extension mechanics that |
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* allow support of new forms of fork/join processing. |
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* <p>A "main" {@code ForkJoinTask} begins execution when submitted |
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* to a {@link ForkJoinPool}. Once started, it will usually in turn |
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* start other subtasks. As indicated by the name of this class, |
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* many programs using {@code ForkJoinTask} employ only methods |
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* {@link #fork} and {@link #join}, or derivatives such as {@link |
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* #invokeAll}. However, this class also provides a number of other |
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* methods that can come into play in advanced usages, as well as |
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* extension mechanics that allow support of new forms of fork/join |
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* processing. |
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* |
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* <p>A ForkJoinTask is a lightweight form of {@link Future}. The |
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* efficiency of ForkJoinTasks stems from a set of restrictions (that |
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* are only partially statically enforceable) reflecting their |
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* intended use as computational tasks calculating pure functions or |
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* operating on purely isolated objects. The primary coordination |
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* mechanisms are {@link #fork}, that arranges asynchronous execution, |
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* and {@link #join}, that doesn't proceed until the task's result has |
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* been computed. Computations should avoid {@code synchronized} |
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* methods or blocks, and should minimize other blocking |
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* synchronization apart from joining other tasks or using |
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* synchronizers such as Phasers that are advertised to cooperate with |
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* fork/join scheduling. Tasks should also not perform blocking IO, |
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* and should ideally access variables that are completely independent |
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* of those accessed by other running tasks. Minor breaches of these |
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* restrictions, for example using shared output streams, may be |
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* tolerable in practice, but frequent use may result in poor |
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* performance, and the potential to indefinitely stall if the number |
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* of threads not waiting for IO or other external synchronization |
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* becomes exhausted. This usage restriction is in part enforced by |
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* not permitting checked exceptions such as {@code IOExceptions} |
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* to be thrown. However, computations may still encounter unchecked |
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* exceptions, that are rethrown to callers attempting join |
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* them. These exceptions may additionally include |
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* RejectedExecutionExceptions stemming from internal resource |
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* exhaustion such as failure to allocate internal task queues. |
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* <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}. |
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* The efficiency of {@code ForkJoinTask}s stems from a set of |
38 |
> |
* restrictions (that are only partially statically enforceable) |
39 |
> |
* reflecting their intended use as computational tasks calculating |
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> |
* pure functions or operating on purely isolated objects. The |
41 |
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* primary coordination mechanisms are {@link #fork}, that arranges |
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* asynchronous execution, and {@link #join}, that doesn't proceed |
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* until the task's result has been computed. Computations should |
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* avoid {@code synchronized} methods or blocks, and should minimize |
45 |
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* other blocking synchronization apart from joining other tasks or |
46 |
> |
* using synchronizers such as Phasers that are advertised to |
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> |
* cooperate with fork/join scheduling. Tasks should also not perform |
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* blocking IO, and should ideally access variables that are |
49 |
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* completely independent of those accessed by other running |
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* tasks. Minor breaches of these restrictions, for example using |
51 |
> |
* shared output streams, may be tolerable in practice, but frequent |
52 |
> |
* use may result in poor performance, and the potential to |
53 |
> |
* indefinitely stall if the number of threads not waiting for IO or |
54 |
> |
* other external synchronization becomes exhausted. This usage |
55 |
> |
* restriction is in part enforced by not permitting checked |
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> |
* exceptions such as {@code IOExceptions} to be thrown. However, |
57 |
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* computations may still encounter unchecked exceptions, that are |
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* rethrown to callers attempting to join them. These exceptions may |
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* additionally include RejectedExecutionExceptions stemming from |
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* internal resource exhaustion such as failure to allocate internal |
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* task queues. |
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* |
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* <p>The primary method for awaiting completion and extracting |
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* results of a task is {@link #join}, but there are several variants: |
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* execute other tasks while awaiting joins, which is sometimes more |
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* efficient but only applies when all subtasks are known to be |
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* strictly tree-structured. Method {@link #invoke} is semantically |
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* equivalent to {@code fork(); join()} but always attempts to |
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* begin execution in the current thread. The "<em>quiet</em>" forms |
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* of these methods do not extract results or report exceptions. These |
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* equivalent to {@code fork(); join()} but always attempts to begin |
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* execution in the current thread. The "<em>quiet</em>" forms of |
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* these methods do not extract results or report exceptions. These |
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* may be useful when a set of tasks are being executed, and you need |
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* to delay processing of results or exceptions until all complete. |
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* Method {@code invokeAll} (available in multiple versions) |
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* performs the most common form of parallel invocation: forking a set |
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* of tasks and joining them all. |
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* |
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* <p> The ForkJoinTask class is not usually directly subclassed. |
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* <p>The execution status of tasks may be queried at several levels |
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* of detail: {@link #isDone} is true if a task completed in any way |
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* (including the case where a task was cancelled without executing); |
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* {@link #isCancelled} is true if completion was due to cancellation; |
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* {@link #isCompletedNormally} is true if a task completed without |
85 |
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* cancellation or encountering an exception; {@link |
86 |
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* #isCompletedExceptionally} is true if if the task encountered an |
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* exception (in which case {@link #getException} returns the |
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> |
* exception); {@link #isCancelled} is true if the task was cancelled |
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* (in which case {@link #getException} returns a {@link |
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* java.util.concurrent.CancellationException}); and {@link |
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* #isCompletedAbnormally} is true if a task was either cancelled or |
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* encountered an exception. |
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* |
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* <p>The ForkJoinTask class is not usually directly subclassed. |
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* Instead, you subclass one of the abstract classes that support a |
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* particular style of fork/join processing. Normally, a concrete |
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* particular style of fork/join processing, typically {@link |
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> |
* RecursiveAction} for computations that do not return results, or |
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* {@link RecursiveTask} for those that do. Normally, a concrete |
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* ForkJoinTask subclass declares fields comprising its parameters, |
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* established in a constructor, and then defines a {@code compute} |
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* method that somehow uses the control methods supplied by this base |
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* class. While these methods have {@code public} access (to allow |
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* instances of different task subclasses to call each others |
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> |
* instances of different task subclasses to call each other's |
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* methods), some of them may only be called from within other |
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* ForkJoinTasks (as may be determined using method {@link |
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* #inForkJoinPool}). Attempts to invoke them in other contexts |
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* result in exceptions or errors, possibly including |
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* ClassCastException. |
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* |
110 |
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* <p>Most base support methods are {@code final} because their |
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* implementations are intrinsically tied to the underlying |
112 |
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* lightweight task scheduling framework, and so cannot be overridden. |
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* Developers creating new basic styles of fork/join processing should |
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* minimally implement {@code protected} methods |
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* {@link #exec}, {@link #setRawResult}, and |
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* {@link #getRawResult}, while also introducing an abstract |
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* computational method that can be implemented in its subclasses, |
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* possibly relying on other {@code protected} methods provided |
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* by this class. |
110 |
> |
* <p>Most base support methods are {@code final}, to prevent |
111 |
> |
* overriding of implementations that are intrinsically tied to the |
112 |
> |
* underlying lightweight task scheduling framework. Developers |
113 |
> |
* creating new basic styles of fork/join processing should minimally |
114 |
> |
* implement {@code protected} methods {@link #exec}, {@link |
115 |
> |
* #setRawResult}, and {@link #getRawResult}, while also introducing |
116 |
> |
* an abstract computational method that can be implemented in its |
117 |
> |
* subclasses, possibly relying on other {@code protected} methods |
118 |
> |
* provided by this class. |
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* |
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* <p>ForkJoinTasks should perform relatively small amounts of |
121 |
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* computations, otherwise splitting into smaller tasks. As a very |
122 |
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* rough rule of thumb, a task should perform more than 100 and less |
123 |
< |
* than 10000 basic computational steps. If tasks are too big, then |
124 |
< |
* parallelism cannot improve throughput. If too small, then memory |
125 |
< |
* and internal task maintenance overhead may overwhelm processing. |
121 |
> |
* computation. Large tasks should be split into smaller subtasks, |
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> |
* usually via recursive decomposition. As a very rough rule of thumb, |
123 |
> |
* a task should perform more than 100 and less than 10000 basic |
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> |
* computational steps. If tasks are too big, then parallelism cannot |
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> |
* improve throughput. If too small, then memory and internal task |
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> |
* maintenance overhead may overwhelm processing. |
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> |
* |
128 |
> |
* <p>This class provides {@code adapt} methods for {@link |
129 |
> |
* java.lang.Runnable} and {@link java.util.concurrent.Callable}, that |
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> |
* may be of use when mixing execution of ForkJoinTasks with other |
131 |
> |
* kinds of tasks. When all tasks are of this form, consider using a |
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* pool in {@link ForkJoinPool#setAsyncMode async mode}. |
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* |
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* <p>ForkJoinTasks are {@code Serializable}, which enables them |
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* to be used in extensions such as remote execution frameworks. It is |
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* in general sensible to serialize tasks only before or after, but |
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* not during execution. Serialization is not relied on during |
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* execution itself. |
134 |
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* <p>ForkJoinTasks are {@code Serializable}, which enables them to be |
135 |
> |
* used in extensions such as remote execution frameworks. It is |
136 |
> |
* sensible to serialize tasks only before or after, but not during, |
137 |
> |
* execution. Serialization is not relied on during execution itself. |
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* |
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* @since 1.7 |
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* @author Doug Lea |
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*/ |
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private V reportFutureResult() |
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throws ExecutionException, InterruptedException { |
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+ |
if (Thread.interrupted()) |
400 |
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throw new InterruptedException(); |
401 |
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int s = status & COMPLETION_MASK; |
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if (s < NORMAL) { |
403 |
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Throwable ex; |
405 |
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throw new CancellationException(); |
406 |
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if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
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throw new ExecutionException(ex); |
382 |
– |
if (Thread.interrupted()) |
383 |
– |
throw new InterruptedException(); |
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} |
409 |
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return getRawResult(); |
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} |
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*/ |
416 |
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private V reportTimedFutureResult() |
417 |
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throws InterruptedException, ExecutionException, TimeoutException { |
418 |
+ |
if (Thread.interrupted()) |
419 |
+ |
throw new InterruptedException(); |
420 |
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Throwable ex; |
421 |
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int s = status & COMPLETION_MASK; |
422 |
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if (s == NORMAL) |
425 |
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throw new CancellationException(); |
426 |
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if (s == EXCEPTIONAL && (ex = exceptionMap.get(this)) != null) |
427 |
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throw new ExecutionException(ex); |
402 |
– |
if (Thread.interrupted()) |
403 |
– |
throw new InterruptedException(); |
428 |
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throw new TimeoutException(); |
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} |
430 |
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|
510 |
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/** |
511 |
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* Arranges to asynchronously execute this task. While it is not |
512 |
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* necessarily enforced, it is a usage error to fork a task more |
513 |
< |
* than once unless it has completed and been reinitialized. This |
490 |
< |
* method may be invoked only from within ForkJoinTask |
491 |
< |
* computations (as may be determined using method {@link |
492 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
493 |
< |
* in exceptions or errors, possibly including ClassCastException. |
513 |
> |
* than once unless it has completed and been reinitialized. |
514 |
|
* |
515 |
< |
* @return {@code this}, to simplify usage. |
515 |
> |
* <p>This method may be invoked only from within {@code |
516 |
> |
* ForkJoinTask} computations (as may be determined using method |
517 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
518 |
> |
* result in exceptions or errors, possibly including {@code |
519 |
> |
* ClassCastException}. |
520 |
> |
* |
521 |
> |
* @return {@code this}, to simplify usage |
522 |
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*/ |
523 |
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public final ForkJoinTask<V> fork() { |
524 |
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((ForkJoinWorkerThread) Thread.currentThread()) |
528 |
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|
529 |
|
/** |
530 |
|
* Returns the result of the computation when it is ready. |
531 |
< |
* This method differs from {@code get} in that abnormal |
532 |
< |
* completion results in RuntimeExceptions or Errors, not |
533 |
< |
* ExecutionExceptions. |
531 |
> |
* This method differs from {@link #get()} in that |
532 |
> |
* abnormal completion results in {@code RuntimeException} or |
533 |
> |
* {@code Error}, not {@code ExecutionException}. |
534 |
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* |
535 |
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* @return the computed result |
536 |
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*/ |
543 |
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|
544 |
|
/** |
545 |
|
* Commences performing this task, awaits its completion if |
546 |
< |
* necessary, and return its result. |
546 |
> |
* necessary, and return its result, or throws an (unchecked) |
547 |
> |
* exception if the underlying computation did so. |
548 |
|
* |
522 |
– |
* @throws Throwable (a RuntimeException, Error, or unchecked |
523 |
– |
* exception) if the underlying computation did so |
549 |
|
* @return the computed result |
550 |
|
*/ |
551 |
|
public final V invoke() { |
556 |
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} |
557 |
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|
558 |
|
/** |
559 |
< |
* Forks both tasks, returning when {@code isDone} holds for |
560 |
< |
* both of them or an exception is encountered. This method may be |
561 |
< |
* invoked only from within ForkJoinTask computations (as may be |
562 |
< |
* determined using method {@link #inForkJoinPool}). Attempts to |
563 |
< |
* invoke in other contexts result in exceptions or errors, |
564 |
< |
* possibly including ClassCastException. |
565 |
< |
* |
566 |
< |
* @param t1 one task |
567 |
< |
* @param t2 the other task |
568 |
< |
* @throws NullPointerException if t1 or t2 are null |
569 |
< |
* @throws RuntimeException or Error if either task did so |
559 |
> |
* Forks the given tasks, returning when {@code isDone} holds for |
560 |
> |
* each task or an (unchecked) exception is encountered, in which |
561 |
> |
* case the exception is rethrown. If more than one task |
562 |
> |
* encounters an exception, then this method throws any one of |
563 |
> |
* these exceptions. The individual status of each task may be |
564 |
> |
* checked using {@link #getException()} and related methods. |
565 |
> |
* |
566 |
> |
* <p>This method may be invoked only from within {@code |
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 {@code |
570 |
> |
* ClassCastException}. |
571 |
> |
* |
572 |
> |
* @param t1 the first task |
573 |
> |
* @param t2 the second task |
574 |
> |
* @throws NullPointerException if any task is null |
575 |
|
*/ |
576 |
< |
public static void invokeAll(ForkJoinTask<?>t1, ForkJoinTask<?> t2) { |
576 |
> |
public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) { |
577 |
|
t2.fork(); |
578 |
|
t1.invoke(); |
579 |
|
t2.join(); |
580 |
|
} |
581 |
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|
582 |
|
/** |
583 |
< |
* Forks the given tasks, returning when {@code isDone} holds |
584 |
< |
* for all of them. If any task encounters an exception, others |
585 |
< |
* may be cancelled. This method may be invoked only from within |
586 |
< |
* ForkJoinTask computations (as may be determined using method |
587 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
588 |
< |
* result in exceptions or errors, possibly including |
589 |
< |
* ClassCastException. |
583 |
> |
* Forks the given tasks, returning when {@code isDone} holds for |
584 |
> |
* each task or an (unchecked) exception is encountered, in which |
585 |
> |
* case the exception is rethrown. If any task encounters an |
586 |
> |
* exception, others may be, but are not guaranteed to be, |
587 |
> |
* cancelled. If more than one task encounters an exception, then |
588 |
> |
* this method throws any one of these exceptions. The individual |
589 |
> |
* status of each task may be checked using {@link #getException()} |
590 |
> |
* and related methods. |
591 |
> |
* |
592 |
> |
* <p>This method may be invoked only from within {@code |
593 |
> |
* ForkJoinTask} computations (as may be determined using method |
594 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
595 |
> |
* result in exceptions or errors, possibly including {@code |
596 |
> |
* ClassCastException}. |
597 |
|
* |
598 |
< |
* @param tasks the array of tasks |
599 |
< |
* @throws NullPointerException if tasks or any element are null |
563 |
< |
* @throws RuntimeException or Error if any task did so |
598 |
> |
* @param tasks the tasks |
599 |
> |
* @throws NullPointerException if any task is null |
600 |
|
*/ |
601 |
|
public static void invokeAll(ForkJoinTask<?>... tasks) { |
602 |
|
Throwable ex = null; |
632 |
|
} |
633 |
|
|
634 |
|
/** |
635 |
< |
* Forks all tasks in the collection, returning when |
636 |
< |
* {@code isDone} holds for all of them. If any task |
637 |
< |
* encounters an exception, others may be cancelled. This method |
638 |
< |
* may be invoked only from within ForkJoinTask computations (as |
639 |
< |
* may be determined using method {@link |
640 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
641 |
< |
* in exceptions or errors, possibly including ClassCastException. |
635 |
> |
* Forks all tasks in the specified collection, returning when |
636 |
> |
* {@code isDone} holds for each task or an (unchecked) exception |
637 |
> |
* is encountered. If any task encounters an exception, others |
638 |
> |
* may be, but are not guaranteed to be, cancelled. If more than |
639 |
> |
* one task encounters an exception, then this method throws any |
640 |
> |
* one of these exceptions. The individual status of each task |
641 |
> |
* may be checked using {@link #getException()} and related |
642 |
> |
* methods. The behavior of this operation is undefined if the |
643 |
> |
* specified collection is modified while the operation is in |
644 |
> |
* progress. |
645 |
> |
* |
646 |
> |
* <p>This method may be invoked only from within {@code |
647 |
> |
* ForkJoinTask} computations (as may be determined using method |
648 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
649 |
> |
* result in exceptions or errors, possibly including {@code |
650 |
> |
* ClassCastException}. |
651 |
|
* |
652 |
|
* @param tasks the collection of tasks |
653 |
|
* @return the tasks argument, to simplify usage |
654 |
|
* @throws NullPointerException if tasks or any element are null |
610 |
– |
* @throws RuntimeException or Error if any task did so |
655 |
|
*/ |
656 |
|
public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) { |
657 |
< |
if (!(tasks instanceof List<?>)) { |
657 |
> |
if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) { |
658 |
|
invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()])); |
659 |
|
return tasks; |
660 |
|
} |
695 |
|
} |
696 |
|
|
697 |
|
/** |
698 |
+ |
* Attempts to cancel execution of this task. This attempt will |
699 |
+ |
* fail if the task has already completed, has already been |
700 |
+ |
* cancelled, or could not be cancelled for some other reason. If |
701 |
+ |
* successful, and this task has not started when cancel is |
702 |
+ |
* called, execution of this task is suppressed, {@link |
703 |
+ |
* #isCancelled} will report true, and {@link #join} will result |
704 |
+ |
* in a {@code CancellationException} being thrown. |
705 |
+ |
* |
706 |
+ |
* <p>This method may be overridden in subclasses, but if so, must |
707 |
+ |
* still ensure that these minimal properties hold. In particular, |
708 |
+ |
* the {@code cancel} method itself must not throw exceptions. |
709 |
+ |
* |
710 |
+ |
* <p>This method is designed to be invoked by <em>other</em> |
711 |
+ |
* tasks. To terminate the current task, you can just return or |
712 |
+ |
* throw an unchecked exception from its computation method, or |
713 |
+ |
* invoke {@link #completeExceptionally}. |
714 |
+ |
* |
715 |
+ |
* @param mayInterruptIfRunning this value is ignored in the |
716 |
+ |
* default implementation because tasks are not |
717 |
+ |
* cancelled via interruption |
718 |
+ |
* |
719 |
+ |
* @return {@code true} if this task is now cancelled |
720 |
+ |
*/ |
721 |
+ |
public boolean cancel(boolean mayInterruptIfRunning) { |
722 |
+ |
setCompletion(CANCELLED); |
723 |
+ |
return (status & COMPLETION_MASK) == CANCELLED; |
724 |
+ |
} |
725 |
+ |
|
726 |
+ |
/** |
727 |
|
* Returns {@code true} if the computation performed by this task |
728 |
|
* has completed (or has been cancelled). |
729 |
|
* |
743 |
|
} |
744 |
|
|
745 |
|
/** |
746 |
< |
* Asserts that the results of this task's computation will not be |
674 |
< |
* used. If a cancellation occurs before attempting to execute this |
675 |
< |
* task, execution will be suppressed, {@link #isCancelled} |
676 |
< |
* will report true, and {@link #join} will result in a |
677 |
< |
* {@code CancellationException} being thrown. Otherwise, when |
678 |
< |
* cancellation races with completion, there are no guarantees |
679 |
< |
* about whether {@code isCancelled} will report {@code true}, |
680 |
< |
* whether {@code join} will return normally or via an exception, |
681 |
< |
* or whether these behaviors will remain consistent upon repeated |
682 |
< |
* invocation. |
683 |
< |
* |
684 |
< |
* <p>This method may be overridden in subclasses, but if so, must |
685 |
< |
* still ensure that these minimal properties hold. In particular, |
686 |
< |
* the cancel method itself must not throw exceptions. |
687 |
< |
* |
688 |
< |
* <p> This method is designed to be invoked by <em>other</em> |
689 |
< |
* tasks. To terminate the current task, you can just return or |
690 |
< |
* throw an unchecked exception from its computation method, or |
691 |
< |
* invoke {@link #completeExceptionally}. |
746 |
> |
* Returns {@code true} if this task threw an exception or was cancelled. |
747 |
|
* |
748 |
< |
* @param mayInterruptIfRunning this value is ignored in the |
749 |
< |
* default implementation because tasks are not in general |
750 |
< |
* cancelled via interruption |
748 |
> |
* @return {@code true} if this task threw an exception or was cancelled |
749 |
> |
*/ |
750 |
> |
public final boolean isCompletedAbnormally() { |
751 |
> |
return (status & COMPLETION_MASK) < NORMAL; |
752 |
> |
} |
753 |
> |
|
754 |
> |
/** |
755 |
> |
* Returns {@code true} if this task completed without throwing an |
756 |
> |
* exception and was not cancelled. |
757 |
|
* |
758 |
< |
* @return {@code true} if this task is now cancelled |
758 |
> |
* @return {@code true} if this task completed without throwing an |
759 |
> |
* exception and was not cancelled |
760 |
|
*/ |
761 |
< |
public boolean cancel(boolean mayInterruptIfRunning) { |
762 |
< |
setCompletion(CANCELLED); |
701 |
< |
return (status & COMPLETION_MASK) == CANCELLED; |
761 |
> |
public final boolean isCompletedNormally() { |
762 |
> |
return (status & COMPLETION_MASK) == NORMAL; |
763 |
|
} |
764 |
|
|
765 |
|
/** |
766 |
< |
* Returns {@code true} if this task threw an exception or was cancelled. |
766 |
> |
* Returns {@code true} if this task threw an exception. |
767 |
|
* |
768 |
< |
* @return {@code true} if this task threw an exception or was cancelled |
768 |
> |
* @return {@code true} if this task threw an exception |
769 |
|
*/ |
770 |
< |
public final boolean isCompletedAbnormally() { |
771 |
< |
return (status & COMPLETION_MASK) < NORMAL; |
770 |
> |
public final boolean isCompletedExceptionally() { |
771 |
> |
return (status & COMPLETION_MASK) == EXCEPTIONAL; |
772 |
|
} |
773 |
|
|
774 |
|
/** |
775 |
|
* Returns the exception thrown by the base computation, or a |
776 |
< |
* CancellationException if cancelled, or null if none or if the |
777 |
< |
* method has not yet completed. |
776 |
> |
* {@code CancellationException} if cancelled, or {@code null} if |
777 |
> |
* none or if the method has not yet completed. |
778 |
|
* |
779 |
|
* @return the exception, or {@code null} if none |
780 |
|
*/ |
793 |
|
* {@code join} and related operations. This method may be used |
794 |
|
* to induce exceptions in asynchronous tasks, or to force |
795 |
|
* completion of tasks that would not otherwise complete. Its use |
796 |
< |
* in other situations is likely to be wrong. This method is |
796 |
> |
* in other situations is discouraged. This method is |
797 |
|
* overridable, but overridden versions must invoke {@code super} |
798 |
|
* implementation to maintain guarantees. |
799 |
|
* |
813 |
|
* operations. This method may be used to provide results for |
814 |
|
* asynchronous tasks, or to provide alternative handling for |
815 |
|
* tasks that would not otherwise complete normally. Its use in |
816 |
< |
* other situations is likely to be wrong. This method is |
816 |
> |
* other situations is discouraged. This method is |
817 |
|
* overridable, but overridden versions must invoke {@code super} |
818 |
|
* implementation to maintain guarantees. |
819 |
|
* |
852 |
|
* there are no potential dependencies between continuation of the |
853 |
|
* current task and that of any other task that might be executed |
854 |
|
* while helping. (This usually holds for pure divide-and-conquer |
855 |
< |
* tasks). This method may be invoked only from within |
856 |
< |
* ForkJoinTask computations (as may be determined using method |
857 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
858 |
< |
* result in exceptions or errors, possibly including |
859 |
< |
* ClassCastException. |
855 |
> |
* tasks). |
856 |
> |
* |
857 |
> |
* <p>This method may be invoked only from within {@code |
858 |
> |
* ForkJoinTask} computations (as may be determined using method |
859 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
860 |
> |
* result in exceptions or errors, possibly including {@code |
861 |
> |
* ClassCastException}. |
862 |
|
* |
863 |
|
* @return the computed result |
864 |
|
*/ |
871 |
|
|
872 |
|
/** |
873 |
|
* Possibly executes other tasks until this task is ready. This |
874 |
< |
* method may be invoked only from within ForkJoinTask |
875 |
< |
* computations (as may be determined using method {@link |
876 |
< |
* #inForkJoinPool}). Attempts to invoke in other contexts result |
877 |
< |
* in exceptions or errors, possibly including ClassCastException. |
874 |
> |
* method may be useful when processing collections of tasks when |
875 |
> |
* some have been cancelled or otherwise known to have aborted. |
876 |
> |
* |
877 |
> |
* <p>This method may be invoked only from within {@code |
878 |
> |
* ForkJoinTask} computations (as may be determined using method |
879 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
880 |
> |
* result in exceptions or errors, possibly including {@code |
881 |
> |
* ClassCastException}. |
882 |
|
*/ |
883 |
|
public final void quietlyHelpJoin() { |
884 |
|
if (status >= 0) { |
917 |
|
|
918 |
|
/** |
919 |
|
* Possibly executes tasks until the pool hosting the current task |
920 |
< |
* {@link ForkJoinPool#isQuiescent}. This method may be of use in |
921 |
< |
* designs in which many tasks are forked, but none are explicitly |
922 |
< |
* joined, instead executing them until all are processed. |
920 |
> |
* {@link ForkJoinPool#isQuiescent is quiescent}. This method may |
921 |
> |
* be of use in designs in which many tasks are forked, but none |
922 |
> |
* are explicitly joined, instead executing them until all are |
923 |
> |
* processed. |
924 |
> |
* |
925 |
> |
* <p>This method may be invoked only from within {@code |
926 |
> |
* ForkJoinTask} computations (as may be determined using method |
927 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
928 |
> |
* result in exceptions or errors, possibly including {@code |
929 |
> |
* ClassCastException}. |
930 |
|
*/ |
931 |
|
public static void helpQuiesce() { |
932 |
|
((ForkJoinWorkerThread) Thread.currentThread()) |
939 |
|
* this task, but only if reuse occurs when this task has either |
940 |
|
* never been forked, or has been forked, then completed and all |
941 |
|
* outstanding joins of this task have also completed. Effects |
942 |
< |
* under any other usage conditions are not guaranteed, and are |
943 |
< |
* almost surely wrong. This method may be useful when executing |
942 |
> |
* under any other usage conditions are not guaranteed. |
943 |
> |
* This method may be useful when executing |
944 |
|
* pre-constructed trees of subtasks in loops. |
945 |
|
*/ |
946 |
|
public void reinitialize() { |
953 |
|
* Returns the pool hosting the current task execution, or null |
954 |
|
* if this task is executing outside of any ForkJoinPool. |
955 |
|
* |
956 |
+ |
* @see #inForkJoinPool |
957 |
|
* @return the pool, or {@code null} if none |
958 |
|
*/ |
959 |
|
public static ForkJoinPool getPool() { |
979 |
|
* by the current thread, and has not commenced executing in |
980 |
|
* another thread. This method may be useful when arranging |
981 |
|
* alternative local processing of tasks that could have been, but |
982 |
< |
* were not, stolen. This method may be invoked only from within |
983 |
< |
* ForkJoinTask computations (as may be determined using method |
984 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
985 |
< |
* result in exceptions or errors, possibly including |
986 |
< |
* ClassCastException. |
982 |
> |
* were not, stolen. |
983 |
> |
* |
984 |
> |
* <p>This method may be invoked only from within {@code |
985 |
> |
* ForkJoinTask} computations (as may be determined using method |
986 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
987 |
> |
* result in exceptions or errors, possibly including {@code |
988 |
> |
* ClassCastException}. |
989 |
|
* |
990 |
|
* @return {@code true} if unforked |
991 |
|
*/ |
1000 |
|
* value may be useful for heuristic decisions about whether to |
1001 |
|
* fork other tasks. |
1002 |
|
* |
1003 |
+ |
* <p>This method may be invoked only from within {@code |
1004 |
+ |
* ForkJoinTask} computations (as may be determined using method |
1005 |
+ |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1006 |
+ |
* result in exceptions or errors, possibly including {@code |
1007 |
+ |
* ClassCastException}. |
1008 |
+ |
* |
1009 |
|
* @return the number of tasks |
1010 |
|
*/ |
1011 |
|
public static int getQueuedTaskCount() { |
1023 |
|
* tasks, and to process computations locally if this threshold is |
1024 |
|
* exceeded. |
1025 |
|
* |
1026 |
+ |
* <p>This method may be invoked only from within {@code |
1027 |
+ |
* ForkJoinTask} computations (as may be determined using method |
1028 |
+ |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1029 |
+ |
* result in exceptions or errors, possibly including {@code |
1030 |
+ |
* ClassCastException}. |
1031 |
+ |
* |
1032 |
|
* @return the surplus number of tasks, which may be negative |
1033 |
|
*/ |
1034 |
|
public static int getSurplusQueuedTaskCount() { |
1064 |
|
* called otherwise. The return value controls whether this task |
1065 |
|
* is considered to be done normally. It may return false in |
1066 |
|
* asynchronous actions that require explicit invocations of |
1067 |
< |
* {@link #complete} to become joinable. It may throw exceptions |
1068 |
< |
* to indicate abnormal exit. |
1067 |
> |
* {@link #complete} to become joinable. It may also throw an |
1068 |
> |
* (unchecked) exception to indicate abnormal exit. |
1069 |
|
* |
1070 |
|
* @return {@code true} if completed normally |
982 |
– |
* @throws Error or RuntimeException if encountered during computation |
1071 |
|
*/ |
1072 |
|
protected abstract boolean exec(); |
1073 |
|
|
1079 |
|
* null even if a task exists but cannot be accessed without |
1080 |
|
* contention with other threads. This method is designed |
1081 |
|
* primarily to support extensions, and is unlikely to be useful |
1082 |
< |
* otherwise. This method may be invoked only from within |
1083 |
< |
* ForkJoinTask computations (as may be determined using method |
1084 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1085 |
< |
* result in exceptions or errors, possibly including |
1086 |
< |
* ClassCastException. |
1082 |
> |
* otherwise. |
1083 |
> |
* |
1084 |
> |
* <p>This method may be invoked only from within {@code |
1085 |
> |
* ForkJoinTask} computations (as may be determined using method |
1086 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1087 |
> |
* result in exceptions or errors, possibly including {@code |
1088 |
> |
* ClassCastException}. |
1089 |
|
* |
1090 |
|
* @return the next task, or {@code null} if none are available |
1091 |
|
*/ |
1098 |
|
* Unschedules and returns, without executing, the next task |
1099 |
|
* queued by the current thread but not yet executed. This method |
1100 |
|
* is designed primarily to support extensions, and is unlikely to |
1101 |
< |
* be useful otherwise. This method may be invoked only from |
1102 |
< |
* within ForkJoinTask computations (as may be determined using |
1103 |
< |
* method {@link #inForkJoinPool}). Attempts to invoke in other |
1104 |
< |
* contexts result in exceptions or errors, possibly including |
1105 |
< |
* ClassCastException. |
1101 |
> |
* be useful otherwise. |
1102 |
> |
* |
1103 |
> |
* <p>This method may be invoked only from within {@code |
1104 |
> |
* ForkJoinTask} computations (as may be determined using method |
1105 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1106 |
> |
* result in exceptions or errors, possibly including {@code |
1107 |
> |
* ClassCastException}. |
1108 |
|
* |
1109 |
|
* @return the next task, or {@code null} if none are available |
1110 |
|
*/ |
1121 |
|
* {@code null} result does not necessarily imply quiescence |
1122 |
|
* of the pool this task is operating in. This method is designed |
1123 |
|
* primarily to support extensions, and is unlikely to be useful |
1124 |
< |
* otherwise. This method may be invoked only from within |
1125 |
< |
* ForkJoinTask computations (as may be determined using method |
1126 |
< |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1127 |
< |
* result in exceptions or errors, possibly including |
1128 |
< |
* ClassCastException. |
1124 |
> |
* otherwise. |
1125 |
> |
* |
1126 |
> |
* <p>This method may be invoked only from within {@code |
1127 |
> |
* ForkJoinTask} computations (as may be determined using method |
1128 |
> |
* {@link #inForkJoinPool}). Attempts to invoke in other contexts |
1129 |
> |
* result in exceptions or errors, possibly including {@code |
1130 |
> |
* ClassCastException}. |
1131 |
|
* |
1132 |
|
* @return a task, or {@code null} if none are available |
1133 |
|
*/ |
1167 |
|
*/ |
1168 |
|
static final class AdaptedCallable<T> extends ForkJoinTask<T> |
1169 |
|
implements RunnableFuture<T> { |
1170 |
< |
final Callable<T> callable; |
1170 |
> |
final Callable<? extends T> callable; |
1171 |
|
T result; |
1172 |
< |
AdaptedCallable(Callable<T> callable) { |
1172 |
> |
AdaptedCallable(Callable<? extends T> callable) { |
1173 |
|
if (callable == null) throw new NullPointerException(); |
1174 |
|
this.callable = callable; |
1175 |
|
} |
1192 |
|
} |
1193 |
|
|
1194 |
|
/** |
1195 |
< |
* Returns a new ForkJoinTask that performs the {@code run} |
1196 |
< |
* method of the given Runnable as its action, and returns a null |
1197 |
< |
* result upon {@code join}. |
1195 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1196 |
> |
* method of the given {@code Runnable} as its action, and returns |
1197 |
> |
* a null result upon {@link #join}. |
1198 |
|
* |
1199 |
|
* @param runnable the runnable action |
1200 |
|
* @return the task |
1201 |
|
*/ |
1202 |
< |
public static ForkJoinTask<Void> adapt(Runnable runnable) { |
1202 |
> |
public static ForkJoinTask<?> adapt(Runnable runnable) { |
1203 |
|
return new AdaptedRunnable<Void>(runnable, null); |
1204 |
|
} |
1205 |
|
|
1206 |
|
/** |
1207 |
< |
* Returns a new ForkJoinTask that performs the {@code run} |
1208 |
< |
* method of the given Runnable as its action, and returns the |
1209 |
< |
* given result upon {@code join}. |
1207 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code run} |
1208 |
> |
* method of the given {@code Runnable} as its action, and returns |
1209 |
> |
* the given result upon {@link #join}. |
1210 |
|
* |
1211 |
|
* @param runnable the runnable action |
1212 |
|
* @param result the result upon completion |
1217 |
|
} |
1218 |
|
|
1219 |
|
/** |
1220 |
< |
* Returns a new ForkJoinTask that performs the {@code call} |
1221 |
< |
* method of the given Callable as its action, and returns its |
1222 |
< |
* result upon {@code join}, translating any checked |
1223 |
< |
* exceptions encountered into {@code RuntimeException}. |
1220 |
> |
* Returns a new {@code ForkJoinTask} that performs the {@code call} |
1221 |
> |
* method of the given {@code Callable} as its action, and returns |
1222 |
> |
* its result upon {@link #join}, translating any checked exceptions |
1223 |
> |
* encountered into {@code RuntimeException}. |
1224 |
|
* |
1225 |
|
* @param callable the callable action |
1226 |
|
* @return the task |
1227 |
|
*/ |
1228 |
< |
public static <T> ForkJoinTask<T> adapt(Callable<T> callable) { |
1228 |
> |
public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) { |
1229 |
|
return new AdaptedCallable<T>(callable); |
1230 |
|
} |
1231 |
|
|