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*/ |
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package jsr166e; |
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|
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/** |
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* A resultless {@link ForkJoinTask} with a completion action |
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* A {@link ForkJoinTask} with a completion action |
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* performed when triggered and there are no remaining pending |
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* actions. Uses of CountedCompleter are similar to those of other |
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* completion based components (such as {@link |
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* decremented; otherwise, the completion action is performed, and if |
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* this completer itself has a completer, the process is continued |
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* with its completer. As is the case with related synchronization |
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* components such as {@link Phaser} and {@link |
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* java.util.concurrent.Semaphore} these methods affect only internal |
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* counts; they do not establish any further internal bookkeeping. In |
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* particular, the identities of pending tasks are not maintained. As |
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* illustrated below, you can create subclasses that do record some or |
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* all pended tasks or their results when needed. |
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* components such as {@link java.util.concurrent.Phaser Phaser} and |
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* {@link java.util.concurrent.Semaphore Semaphore}, these methods |
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* affect only internal counts; they do not establish any further |
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* internal bookkeeping. In particular, the identities of pending |
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* tasks are not maintained. As illustrated below, you can create |
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* subclasses that do record some or all pending tasks or their |
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* results when needed. |
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* |
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* <p>A concrete CountedCompleter class must define method {@link |
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* #compute}, that should, in almost all use cases, invoke {@code |
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* normal completion, and method {@link #onExceptionalCompletion} to |
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* perform an action upon any exception. |
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* |
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* <p>CountedCompleters most often do not bear results, in which case |
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* they are normally declared as {@code CountedCompleter<Void>}, and |
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* will always return {@code null} as a result value. In other cases, |
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* you should override method {@link #getRawResult} to provide a |
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* result from {@code join(), invoke()}, and related methods. (Method |
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* {@link #setRawResult} by default plays no role in CountedCompleters |
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* but may be overridden for example to maintain fields holding result |
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* data.) |
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* |
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* <p>A CountedCompleter that does not itself have a completer (i.e., |
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* one for which {@link #getCompleter} returns {@code null}) can be |
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* used as a regular ForkJoinTask with this added functionality. |
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* <p><b>Parallel recursive decomposition.</b> CountedCompleters may |
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* be arranged in trees similar to those often used with {@link |
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* RecursiveAction}s, although the constructions involved in setting |
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* them up typically vary. Even though they entail a bit more |
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* them up typically vary. Here, the completer of each task is its |
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* parent in the computation tree. Even though they entail a bit more |
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* bookkeeping, CountedCompleters may be better choices when applying |
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* a possibly time-consuming operation (that cannot be further |
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* subdivided) to each element of an array or collection; especially |
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* <pre> {@code |
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* class MyOperation<E> { void apply(E e) { ... } } |
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* |
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* class ForEach<E> extends CountedCompleter { |
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* class ForEach<E> extends CountedCompleter<Void> { |
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* |
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* public static <E> void forEach(ForkJoinPool pool, E[] array, MyOperation<E> op) { |
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* pool.invoke(new ForEach<E>(null, array, op, 0, array.length)); |
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* } |
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* |
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* final E[] array; final MyOperation<E> op; final int lo, hi; |
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* ForEach(CountedCompleter p, E[] array, MyOperation<E> op, int lo, int hi) { |
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* ForEach(CountedCompleter<?> p, E[] array, MyOperation<E> op, int lo, int hi) { |
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* super(p); |
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* this.array = array; this.op = op; this.lo = lo; this.hi = hi; |
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* } |
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* |
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* As a further improvement, notice that the left task need not even |
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* exist. Instead of creating a new one, we can iterate using the |
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* original task, and add a pending count for each fork: |
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* original task, and add a pending count for each fork. Additionally, |
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* this version uses {@code helpComplete} to streamline assistance in |
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* the execution of forked tasks. |
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* |
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* <pre> {@code |
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* class ForEach<E> ... |
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* } |
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* if (h > l) |
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* op.apply(array[l]); |
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* tryComplete(); |
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* helpComplete(); |
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* } |
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* }</pre> |
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* |
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* and reductions are all of type {@code E}), one way to do this in |
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* divide and conquer designs is to have each subtask record its |
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* sibling, so that it can be accessed in method {@code onCompletion}. |
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* For clarity, this class uses explicit left and right subtasks, but |
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* variants of other streamlinings seen in the above example may also |
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* apply. |
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* This technique applies to reductions in which the order of |
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* combining left and right results does not matter; ordered |
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* reductions require explicit left/right designations. Variants of |
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* other streamlinings seen in the above examples may also apply. |
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* |
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* <pre> {@code |
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* class MyMapper<E> { E apply(E v) { ... } } |
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* class MyReducer<E> { E apply(E x, E y) { ... } } |
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* class MapReducer<E> extends CountedCompleter { |
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* class MapReducer<E> extends CountedCompleter<E> { |
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* final E[] array; final MyMapper<E> mapper; |
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* final MyReducer<E> reducer; final int lo, hi; |
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* MapReducer sibling; |
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* MapReducer<E> sibling; |
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* E result; |
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* MapReducer(CountedCompleter p, E[] array, MyMapper<E> mapper, |
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* MyReducer<E> reducer, int lo, int hi) { |
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* result = reducer.apply(child.result, sib.result); |
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* } |
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* } |
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* public E getRawResult() { return result; } |
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* |
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* public static <E> E mapReduce(ForkJoinPool pool, E[] array, |
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* MyMapper<E> mapper, MyReducer<E> reducer) { |
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* MapReducer<E> mr = new MapReducer<E>(null, array, mapper, |
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* reducer, 0, array.length); |
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* pool.invoke(mr); |
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* return mr.result; |
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* return pool.invoke(new MapReducer<E>(null, array, mapper, |
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* reducer, 0, array.length)); |
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* } |
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* } }</pre> |
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* |
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* triggers another async task. For example: |
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* |
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* <pre> {@code |
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* class HeaderBuilder extends CountedCompleter { ... } |
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* class BodyBuilder extends CountedCompleter { ... } |
240 |
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* class PacketSender extends CountedCompleter { |
238 |
> |
* class HeaderBuilder extends CountedCompleter<...> { ... } |
239 |
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* class BodyBuilder extends CountedCompleter<...> { ... } |
240 |
> |
* class PacketSender extends CountedCompleter<...> { |
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* PacketSender(...) { super(null, 1); ... } // trigger on second completion |
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* public void compute() { } // never called |
243 |
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* public void onCompletion(CountedCompleter caller) { sendPacket(); } |
243 |
> |
* public void onCompletion(CountedCompleter<?> caller) { sendPacket(); } |
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* } |
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* // sample use: |
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* PacketSender p = new PacketSender(); |
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* @since 1.8 |
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* @author Doug Lea |
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*/ |
254 |
< |
public abstract class CountedCompleter extends ForkJoinTask<Void> { |
254 |
> |
public abstract class CountedCompleter<T> extends ForkJoinTask<T> { |
255 |
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private static final long serialVersionUID = 5232453752276485070L; |
256 |
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|
257 |
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/** This task's completer, or null if none */ |
258 |
< |
final CountedCompleter completer; |
258 |
> |
final CountedCompleter<?> completer; |
259 |
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/** The number of pending tasks until completion */ |
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volatile int pending; |
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|
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* @param completer this tasks completer, or {@code null} if none |
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* @param initialPendingCount the initial pending count |
268 |
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*/ |
269 |
< |
protected CountedCompleter(CountedCompleter completer, |
269 |
> |
protected CountedCompleter(CountedCompleter<?> completer, |
270 |
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int initialPendingCount) { |
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this.completer = completer; |
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this.pending = initialPendingCount; |
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* |
279 |
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* @param completer this tasks completer, or {@code null} if none |
280 |
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*/ |
281 |
< |
protected CountedCompleter(CountedCompleter completer) { |
281 |
> |
protected CountedCompleter(CountedCompleter<?> completer) { |
282 |
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this.completer = completer; |
283 |
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} |
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|
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* @param caller the task invoking this method (which may |
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* be this task itself). |
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*/ |
307 |
< |
public void onCompletion(CountedCompleter caller) { |
307 |
> |
public void onCompletion(CountedCompleter<?> caller) { |
308 |
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} |
309 |
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|
310 |
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/** |
324 |
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* @return true if this exception should be propagated to this |
325 |
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* tasks completer, if one exists. |
326 |
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*/ |
327 |
< |
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter caller) { |
327 |
> |
public boolean onExceptionalCompletion(Throwable ex, CountedCompleter<?> caller) { |
328 |
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return true; |
329 |
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} |
330 |
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|
334 |
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* |
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* @return the completer |
336 |
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*/ |
337 |
< |
public final CountedCompleter getCompleter() { |
337 |
> |
public final CountedCompleter<?> getCompleter() { |
338 |
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return completer; |
339 |
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} |
340 |
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|
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} |
380 |
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|
381 |
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/** |
382 |
+ |
* Returns the root of the current computation; i.e., this |
383 |
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* task if it has no completer, else its completer's root. |
384 |
+ |
* |
385 |
+ |
* @return the root of the current computation |
386 |
+ |
*/ |
387 |
+ |
public final CountedCompleter<?> getRoot() { |
388 |
+ |
CountedCompleter<?> a = this, p; |
389 |
+ |
while ((p = a.completer) != null) |
390 |
+ |
a = p; |
391 |
+ |
return a; |
392 |
+ |
} |
393 |
+ |
|
394 |
+ |
/** |
395 |
|
* If the pending count is nonzero, decrements the count; |
396 |
|
* otherwise invokes {@link #onCompletion} and then similarly |
397 |
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* tries to complete this task's completer, if one exists, |
398 |
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* else marks this task as complete. |
399 |
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*/ |
400 |
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public final void tryComplete() { |
401 |
< |
CountedCompleter a = this, s = a; |
401 |
> |
CountedCompleter<?> a = this, s = a; |
402 |
|
for (int c;;) { |
403 |
|
if ((c = a.pending) == 0) { |
404 |
|
a.onCompletion(s); |
413 |
|
} |
414 |
|
|
415 |
|
/** |
416 |
+ |
* Identical to {@link #tryComplete}, but may additionally execute |
417 |
+ |
* other tasks within the current computation (i.e., those |
418 |
+ |
* with the same {@link #getRoot}. |
419 |
+ |
*/ |
420 |
+ |
public final void helpComplete() { |
421 |
+ |
CountedCompleter<?> a = this, s = a; |
422 |
+ |
for (int c;;) { |
423 |
+ |
if ((c = a.pending) == 0) { |
424 |
+ |
a.onCompletion(s); |
425 |
+ |
if ((a = (s = a).completer) == null) { |
426 |
+ |
s.quietlyComplete(); |
427 |
+ |
return; |
428 |
+ |
} |
429 |
+ |
} |
430 |
+ |
else if (U.compareAndSwapInt(a, PENDING, c, c - 1)) { |
431 |
+ |
CountedCompleter<?> root = a.getRoot(); |
432 |
+ |
Thread thread = Thread.currentThread(); |
433 |
+ |
ForkJoinPool.WorkQueue wq = |
434 |
+ |
(thread instanceof ForkJoinWorkerThread)? |
435 |
+ |
((ForkJoinWorkerThread)thread).workQueue : null; |
436 |
+ |
ForkJoinTask<?> t; |
437 |
+ |
while ((t = (wq != null) ? wq.popCC(root) : |
438 |
+ |
ForkJoinPool.popCCFromCommonPool(root)) != null) { |
439 |
+ |
t.doExec(); |
440 |
+ |
if (root.isDone()) |
441 |
+ |
break; |
442 |
+ |
} |
443 |
+ |
return; |
444 |
+ |
} |
445 |
+ |
} |
446 |
+ |
} |
447 |
+ |
|
448 |
+ |
/** |
449 |
|
* Regardless of pending count, invokes {@link #onCompletion}, |
450 |
< |
* marks this task as complete with a {@code null} return value, |
451 |
< |
* and further triggers {@link #tryComplete} on this task's |
452 |
< |
* completer, if one exists. This method may be useful when |
453 |
< |
* forcing completion as soon as any one (versus all) of several |
454 |
< |
* subtask results are obtained. |
450 |
> |
* marks this task as complete and further triggers {@link |
451 |
> |
* #tryComplete} on this task's completer, if one exists. This |
452 |
> |
* method may be useful when forcing completion as soon as any one |
453 |
> |
* (versus all) of several subtask results are obtained. The |
454 |
> |
* given rawResult is used as an argument to {@link #setRawResult} |
455 |
> |
* before marking this task as complete; its value is meaningful |
456 |
> |
* only for classes overriding {@code setRawResult}. |
457 |
|
* |
458 |
< |
* @param mustBeNull the {@code null} completion value |
458 |
> |
* @param rawResult the raw result |
459 |
|
*/ |
460 |
< |
public void complete(Void mustBeNull) { |
461 |
< |
CountedCompleter p; |
460 |
> |
public void complete(T rawResult) { |
461 |
> |
CountedCompleter<?> p; |
462 |
|
onCompletion(this); |
463 |
+ |
setRawResult(rawResult); |
464 |
|
quietlyComplete(); |
465 |
|
if ((p = completer) != null) |
466 |
|
p.tryComplete(); |
470 |
|
* Support for FJT exception propagation |
471 |
|
*/ |
472 |
|
void internalPropagateException(Throwable ex) { |
473 |
< |
CountedCompleter a = this, s = a; |
473 |
> |
CountedCompleter<?> a = this, s = a; |
474 |
|
while (a.onExceptionalCompletion(ex, s) && |
475 |
|
(a = (s = a).completer) != null && a.status >= 0) |
476 |
|
a.recordExceptionalCompletion(ex); |
485 |
|
} |
486 |
|
|
487 |
|
/** |
488 |
< |
* Always returns {@code null}. |
488 |
> |
* Returns the result of the computation. By default |
489 |
> |
* returns {@code null}, which is appropriate for {@code Void} |
490 |
> |
* actions, but in other cases should be overridden. |
491 |
|
* |
492 |
< |
* @return {@code null} always |
492 |
> |
* @return the result of the computation |
493 |
|
*/ |
494 |
< |
public final Void getRawResult() { return null; } |
494 |
> |
public T getRawResult() { return null; } |
495 |
|
|
496 |
|
/** |
497 |
< |
* Requires null completion value. |
497 |
> |
* A method that result-bearing CountedCompleters may optionally |
498 |
> |
* use to help maintain result data. By default, does nothing. |
499 |
|
*/ |
500 |
< |
protected final void setRawResult(Void mustBeNull) { } |
500 |
> |
protected void setRawResult(T t) { } |
501 |
|
|
502 |
|
// Unsafe mechanics |
503 |
|
private static final sun.misc.Unsafe U; |
512 |
|
} |
513 |
|
} |
514 |
|
|
451 |
– |
|
515 |
|
/** |
516 |
|
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package. |
517 |
|
* Replace with a simple call to Unsafe.getUnsafe when integrating |