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*/ |
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package jsr166y; |
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+ |
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import java.io.Serializable; |
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import java.util.Collection; |
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import java.util.List; |
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* but doing do requires three further considerations: (1) Completion |
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* of few if any <em>other</em> tasks should be dependent on a task |
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* that blocks on external synchronization or IO. Event-style async |
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< |
* tasks that are never joined often fall into this category. (2) To |
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* minimize resource impact, tasks should be small; ideally performing |
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* only the (possibly) blocking action. (3) Unless the {@link |
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* tasks that are never joined (for example, those subclassing {@link |
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* CountedCompleter}) often fall into this category. (2) To minimize |
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* resource impact, tasks should be small; ideally performing only the |
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* (possibly) blocking action. (3) Unless the {@link |
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* ForkJoinPool.ManagedBlocker} API is used, or the number of possibly |
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* blocked tasks is known to be less than the pool's {@link |
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* ForkJoinPool#getParallelism} level, the pool cannot guarantee that |
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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, 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 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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* {@code ClassCastException}. |
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* RecursiveAction} for most computations that do not return results, |
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* {@link RecursiveTask} for those that do, and {@link |
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* CountedCompleter} for those in which completed actions trigger |
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* other actions. Normally, a concrete ForkJoinTask subclass declares |
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* fields comprising its parameters, established in a constructor, and |
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* then defines a {@code compute} method that somehow uses the control |
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* methods supplied by this base class. While these methods have |
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* {@code public} access (to allow instances of different task |
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* subclasses to call each other's methods), some of them may only be |
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* called from within other ForkJoinTasks (as may be determined using |
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* method {@link #inForkJoinPool}). Attempts to invoke them in other |
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* contexts result in exceptions or errors, possibly including {@code |
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* ClassCastException}. |
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* |
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* <p>Method {@link #join} and its variants are appropriate for use |
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* only when completion dependencies are acyclic; that is, the |
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* {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that |
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* may be of use in constructing custom subclasses for problems that |
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* are not statically structured as DAGs. To support such usages a |
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* ForkJoinTask may be atomically <em>tagged</em> with a {@code |
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* short} value using {@link #setForkJoinTaskTag} or {@link |
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> |
* ForkJoinTask may be atomically <em>tagged</em> with a {@code short} |
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* value using {@link #setForkJoinTaskTag} or {@link |
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* #compareAndSetForkJoinTaskTag} and checked using {@link |
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* #getForkJoinTaskTag}. The ForkJoinTask implementation does not |
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* use these {@code protected} methods or tags for any purpose, but |
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* they may be of use in the construction of specialized subclasses. |
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* For example, parallel graph traversals can use the supplied methods |
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* to avoid revisiting nodes/tasks that have already been processed. |
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* Also, completion based designs can use them to record that subtasks |
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* have completed. (Method names for tagging are bulky in part to |
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* encourage definition of methods that reflect their usage patterns.) |
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* #getForkJoinTaskTag}. The ForkJoinTask implementation does not use |
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* these {@code protected} methods or tags for any purpose, but they |
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> |
* may be of use in the construction of specialized subclasses. For |
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* example, parallel graph traversals can use the supplied methods to |
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* avoid revisiting nodes/tasks that have already been processed. |
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* (Method names for tagging are bulky in part to encourage definition |
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* of methods that reflect their usage patterns.) |
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* |
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* <p>Most base support methods are {@code final}, to prevent |
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* overriding of implementations that are intrinsically tied to the |
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} |
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|
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/** |
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* Tries to set SIGNAL status. Used by ForkJoinPool. Other |
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* variants are directly incorporated into externalAwaitDone etc. |
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> |
* Tries to set SIGNAL status unless already completed. Used by |
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> |
* ForkJoinPool. Other variants are directly incorporated into |
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* externalAwaitDone etc. |
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* |
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* @return true if successful |
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*/ |
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final boolean trySetSignal() { |
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< |
int s; |
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< |
return U.compareAndSwapInt(this, STATUS, s = status, s | SIGNAL); |
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> |
int s = status; |
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return s >= 0 && U.compareAndSwapInt(this, STATUS, s, s | SIGNAL); |
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} |
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|
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/** |
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} |
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/** |
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* Records exception and sets exceptional completion. |
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> |
* Records exception and sets status. |
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* |
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* @return status on exit |
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*/ |
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< |
private int setExceptionalCompletion(Throwable ex) { |
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< |
int h = System.identityHashCode(this); |
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< |
final ReentrantLock lock = exceptionTableLock; |
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< |
lock.lock(); |
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< |
try { |
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< |
expungeStaleExceptions(); |
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< |
ExceptionNode[] t = exceptionTable; |
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< |
int i = h & (t.length - 1); |
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< |
for (ExceptionNode e = t[i]; ; e = e.next) { |
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if (e == null) { |
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t[i] = new ExceptionNode(this, ex, t[i]); |
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< |
break; |
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> |
final int recordExceptionalCompletion(Throwable ex) { |
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> |
int s; |
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> |
if ((s = status) >= 0) { |
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> |
int h = System.identityHashCode(this); |
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> |
final ReentrantLock lock = exceptionTableLock; |
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> |
lock.lock(); |
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> |
try { |
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> |
expungeStaleExceptions(); |
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> |
ExceptionNode[] t = exceptionTable; |
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> |
int i = h & (t.length - 1); |
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> |
for (ExceptionNode e = t[i]; ; e = e.next) { |
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if (e == null) { |
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> |
t[i] = new ExceptionNode(this, ex, t[i]); |
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> |
break; |
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> |
} |
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if (e.get() == this) // already present |
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> |
break; |
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} |
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< |
if (e.get() == this) // already present |
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< |
break; |
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> |
} finally { |
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> |
lock.unlock(); |
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} |
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< |
} finally { |
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< |
lock.unlock(); |
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> |
s = setCompletion(EXCEPTIONAL); |
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} |
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< |
return setCompletion(EXCEPTIONAL); |
| 442 |
> |
return s; |
| 443 |
> |
} |
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> |
|
| 445 |
> |
/** |
| 446 |
> |
* Records exception and possibly propagates |
| 447 |
> |
* |
| 448 |
> |
* @return status on exit |
| 449 |
> |
*/ |
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> |
private int setExceptionalCompletion(Throwable ex) { |
| 451 |
> |
int s = recordExceptionalCompletion(ex); |
| 452 |
> |
if ((s & DONE_MASK) == EXCEPTIONAL) |
| 453 |
> |
internalPropagateException(ex); |
| 454 |
> |
return s; |
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> |
} |
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> |
|
| 457 |
> |
/** |
| 458 |
> |
* Hook for exception propagation support for tasks with completers. |
| 459 |
> |
*/ |
| 460 |
> |
void internalPropagateException(Throwable ex) { |
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} |
| 462 |
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|
| 463 |
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/** |
| 539 |
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Throwable ex; |
| 540 |
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if (e == null || (ex = e.ex) == null) |
| 541 |
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return null; |
| 542 |
< |
if (e.thrower != Thread.currentThread().getId()) { |
| 542 |
> |
if (false && e.thrower != Thread.currentThread().getId()) { |
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Class<? extends Throwable> ec = ex.getClass(); |
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try { |
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Constructor<?> noArgCtor = null; |
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} |
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/** |
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< |
* Completes this task. The most recent value established by |
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< |
* {@link #setRawResult} (or {@code null}) will be returned as the |
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< |
* result of subsequent invocations of {@code join} and related |
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< |
* operations. This method may be useful when processing sets of |
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< |
* tasks when some do not otherwise complete normally. Its use in |
| 937 |
< |
* other situations is discouraged. |
| 932 |
> |
* Completes this task normally without setting a value. The most |
| 933 |
> |
* recent value established by {@link #setRawResult} (or {@code |
| 934 |
> |
* null} by default) will be returned as the result of subsequent |
| 935 |
> |
* invocations of {@code join} and related operations. |
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> |
* |
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> |
* @since 1.8 |
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*/ |
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|
public final void quietlyComplete() { |
| 940 |
|
setCompletion(NORMAL); |
| 1259 |
|
protected abstract void setRawResult(V value); |
| 1260 |
|
|
| 1261 |
|
/** |
| 1262 |
< |
* Immediately performs the base action of this task. This method |
| 1263 |
< |
* is designed to support extensions, and should not in general be |
| 1264 |
< |
* called otherwise. The return value controls whether this task |
| 1265 |
< |
* is considered to be done normally. It may return false in |
| 1262 |
> |
* Immediately performs the base action of this task and returns |
| 1263 |
> |
* true if, upon return from this method, this task is guaranteed |
| 1264 |
> |
* to have completed normally. This method may return false |
| 1265 |
> |
* otherwise, to indicate that this task is not necessarily |
| 1266 |
> |
* complete (or is not known to be complete), for example in |
| 1267 |
|
* asynchronous actions that require explicit invocations of |
| 1268 |
< |
* {@link #complete} to become joinable. It may also throw an |
| 1269 |
< |
* (unchecked) exception to indicate abnormal exit. |
| 1268 |
> |
* completion methods. This method may also throw an (unchecked) |
| 1269 |
> |
* exception to indicate abnormal exit. This method is designed to |
| 1270 |
> |
* support extensions, and should not in general be called |
| 1271 |
> |
* otherwise. |
| 1272 |
|
* |
| 1273 |
< |
* @return {@code true} if completed normally |
| 1273 |
> |
* @return {@code true} if this task is known to have completed normally |
| 1274 |
|
*/ |
| 1275 |
|
protected abstract boolean exec(); |
| 1276 |
|
|
