/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/publicdomain/zero/1.0/
*/
package molecule.jsr166y;
import molecule.platform.ThreadFactory;
/**
* A thread managed by a {@link ForkJoinPool}, which executes
* {@link ForkJoinTask}s.
* This class is subclassable solely for the sake of adding
* functionality -- there are no overridable methods dealing with
* scheduling or execution. However, you can override initialization
* and termination methods surrounding the main task processing loop.
* If you do create such a subclass, you will also need to supply a
* custom {@link ForkJoinPool.ForkJoinWorkerThreadFactory} to use it
* in a {@code ForkJoinPool}.
*
* @since 1.7
* @author Doug Lea
*/
public class ForkJoinWorkerThread implements Runnable {
/*
* ForkJoinWorkerThreads are managed by ForkJoinPools and perform
* ForkJoinTasks. For explanation, see the internal documentation
* of class ForkJoinPool.
*
* This class just maintains links to its pool and WorkQueue. The
* pool field is set immediately upon construction, but the
* workQueue field is not set until a call to registerWorker
* completes. This leads to a visibility race, that is tolerated
* by requiring that the workQueue field is only accessed by the
* owning thread.
*/
final ForkJoinPool pool; // the pool this thread works in
final ForkJoinPool.WorkQueue workQueue; // work-stealing mechanics
public final Thread thread;
/**
* Creates a ForkJoinWorkerThread operating in the given pool.
*
* @param pool the pool this thread works in
* @throws NullPointerException if pool is null
*/
protected ForkJoinWorkerThread(final ForkJoinPool pool) {
this(pool, new ThreadFactory("fork-join", true));
}
public ForkJoinWorkerThread(ForkJoinPool pool, ThreadFactory factory) {
// Use a placeholder until a useful name can be set in registerWorker
// super("aForkJoinWorkerThread");
this.thread = factory.newThread(this);
this.pool = pool;
this.workQueue = pool.registerWorker(this);
}
public void start() {
this.thread.start();
}
/**
* Returns the pool hosting this thread.
*
* @return the pool
*/
public ForkJoinPool getPool() {
return pool;
}
/**
* Returns the index number of this thread in its pool. The
* returned value ranges from zero to the maximum number of
* threads (minus one) that have ever been created in the pool.
* This method may be useful for applications that track status or
* collect results per-worker rather than per-task.
*
* @return the index number
*/
public int getPoolIndex() {
return workQueue.poolIndex;
}
/**
* Initializes internal state after construction but before
* processing any tasks. If you override this method, you must
* invoke {@code super.onStart()} at the beginning of the method.
* Initialization requires care: Most fields must have legal
* default values, to ensure that attempted accesses from other
* threads work correctly even before this thread starts
* processing tasks.
*/
protected void onStart() {
}
/**
* Performs cleanup associated with termination of this worker
* thread. If you override this method, you must invoke
* {@code super.onTermination} at the end of the overridden method.
*
* @param exception the exception causing this thread to abort due
* to an unrecoverable error, or {@code null} if completed normally
*/
protected void onTermination(Throwable exception) {
}
/**
* This method is required to be public, but should never be
* called explicitly. It performs the main run loop to execute
* {@link ForkJoinTask}s.
*/
public void run() {
Throwable exception = null;
try {
onStart();
pool.runWorker(workQueue);
} catch (Throwable ex) {
exception = ex;
} finally {
try {
onTermination(exception);
} catch (Throwable ex) {
if (exception == null)
exception = ex;
} finally {
pool.deregisterWorker(this, exception);
}
}
}
}