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/* |
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* Written by Doug Lea with assistance from members of JCP JSR-166 |
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* Expert Group and released to the public domain, as explained at |
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* http://creativecommons.org/publicdomain/zero/1.0/ |
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*/ |
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|
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package jsr166e; |
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|
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/** |
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* A thread managed by a {@link ForkJoinPool}, which executes |
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* {@link ForkJoinTask}s. |
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* This class is subclassable solely for the sake of adding |
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* functionality -- there are no overridable methods dealing with |
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* scheduling or execution. However, you can override initialization |
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* and termination methods surrounding the main task processing loop. |
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* If you do create such a subclass, you will also need to supply a |
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* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to |
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* {@linkplain ForkJoinPool#ForkJoinPool use it} in a {@code ForkJoinPool}. |
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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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public class ForkJoinWorkerThread extends Thread { |
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/* |
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* ForkJoinWorkerThreads are managed by ForkJoinPools and perform |
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* ForkJoinTasks. For explanation, see the internal documentation |
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* of class ForkJoinPool. |
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* |
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* This class just maintains links to its pool and WorkQueue. The |
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* pool field is set immediately upon construction, but the |
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* workQueue field is not set until a call to registerWorker |
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* completes. This leads to a visibility race, that is tolerated |
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* by requiring that the workQueue field is only accessed by the |
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* owning thread. |
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*/ |
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|
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final ForkJoinPool pool; // the pool this thread works in |
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final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics |
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|
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/** |
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* Creates a ForkJoinWorkerThread operating in the given pool. |
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* |
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* @param pool the pool this thread works in |
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* @throws NullPointerException if pool is null |
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*/ |
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protected ForkJoinWorkerThread(ForkJoinPool pool) { |
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// Use a placeholder until a useful name can be set in registerWorker |
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super("aForkJoinWorkerThread"); |
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this.pool = pool; |
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this.workQueue = pool.registerWorker(this); |
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} |
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|
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/** |
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* Returns the pool hosting this thread. |
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* |
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* @return the pool |
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*/ |
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public ForkJoinPool getPool() { |
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return pool; |
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} |
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|
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/** |
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* Returns the unique index number of this thread in its pool. |
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* The returned value ranges from zero to the maximum number of |
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* threads (minus one) that may exist in the pool, and does not |
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* change during the lifetime of the thread. This method may be |
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* useful for applications that track status or collect results |
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* per-worker-thread rather than per-task. |
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* |
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* @return the index number |
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*/ |
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public int getPoolIndex() { |
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return workQueue.poolIndex >>> 1; // ignore odd/even tag bit |
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} |
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|
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/** |
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* Initializes internal state after construction but before |
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* processing any tasks. If you override this method, you must |
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* invoke {@code super.onStart()} at the beginning of the method. |
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* Initialization requires care: Most fields must have legal |
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* default values, to ensure that attempted accesses from other |
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* threads work correctly even before this thread starts |
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* processing tasks. |
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*/ |
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protected void onStart() { |
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} |
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|
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/** |
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* Performs cleanup associated with termination of this worker |
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* thread. If you override this method, you must invoke |
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* {@code super.onTermination} at the end of the overridden method. |
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* |
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* @param exception the exception causing this thread to abort due |
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* to an unrecoverable error, or {@code null} if completed normally |
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*/ |
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protected void onTermination(Throwable exception) { |
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} |
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|
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/** |
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* This method is required to be public, but should never be |
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* called explicitly. It performs the main run loop to execute |
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* {@link ForkJoinTask}s. |
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*/ |
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public void run() { |
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Throwable exception = null; |
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try { |
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onStart(); |
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pool.runWorker(workQueue); |
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} catch (Throwable ex) { |
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exception = ex; |
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} finally { |
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try { |
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onTermination(exception); |
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} catch (Throwable ex) { |
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if (exception == null) |
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exception = ex; |
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} finally { |
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pool.deregisterWorker(this, exception); |
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} |
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} |
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} |
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} |
