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8234131: Miscellaneous changes imported from jsr166 CVS 2021-01

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8257671: ThreadPoolExecutor.Discard*Policy: rejected tasks are not cancelled

Reviewed-by: alanb, prappo, dl
This commit is contained in:
Martin Buchholz 2021-01-09 21:59:27 +00:00
parent 63e3bd7613
commit 270014ab4e
41 changed files with 273 additions and 207 deletions
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38
src/java.base/share/classes/java/util/concurrent/ThreadPoolExecutor.java
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@ -221,13 +221,18 @@ import java.util.concurrent.locks.ReentrantLock;
* simple feedback control mechanism that will slow down the rate that
* new tasks are submitted.
*
* <li>In {@link ThreadPoolExecutor.DiscardPolicy}, a task that
* cannot be executed is simply dropped.
* <li>In {@link ThreadPoolExecutor.DiscardPolicy}, a task that cannot
* be executed is simply dropped. This policy is designed only for
* those rare cases in which task completion is never relied upon.
*
* <li>In {@link ThreadPoolExecutor.DiscardOldestPolicy}, if the
* executor is not shut down, the task at the head of the work queue
* is dropped, and then execution is retried (which can fail again,
* causing this to be repeated.)
* causing this to be repeated.) This policy is rarely acceptable. In
* nearly all cases, you should also cancel the task to cause an
* exception in any component waiting for its completion, and/or log
* the failure, as illustrated in {@link
* ThreadPoolExecutor.DiscardOldestPolicy} documentation.
*
* </ol>
*
@ -272,7 +277,7 @@ import java.util.concurrent.locks.ReentrantLock;
*
* </dl>
*
* <p><b>Extension example</b>. Most extensions of this class
* <p><b>Extension example.</b> Most extensions of this class
* override one or more of the protected hook methods. For example,
* here is a subclass that adds a simple pause/resume feature:
*
@ -1149,8 +1154,10 @@ public class ThreadPoolExecutor extends AbstractExecutorService {
/**
* Creates a new {@code ThreadPoolExecutor} with the given initial
* parameters, the default thread factory and the default rejected
* execution handler.
* parameters, the
* {@linkplain Executors#defaultThreadFactory default thread factory}
* and the {@linkplain ThreadPoolExecutor.AbortPolicy
* default rejected execution handler}.
*
* <p>It may be more convenient to use one of the {@link Executors}
* factory methods instead of this general purpose constructor.
@ -1184,7 +1191,7 @@ public class ThreadPoolExecutor extends AbstractExecutorService {
/**
* Creates a new {@code ThreadPoolExecutor} with the given initial
* parameters and {@linkplain ThreadPoolExecutor.AbortPolicy
* parameters and the {@linkplain ThreadPoolExecutor.AbortPolicy
* default rejected execution handler}.
*
* @param corePoolSize the number of threads to keep in the pool, even
@ -1220,7 +1227,7 @@ public class ThreadPoolExecutor extends AbstractExecutorService {
/**
* Creates a new {@code ThreadPoolExecutor} with the given initial
* parameters and
* parameters and the
* {@linkplain Executors#defaultThreadFactory default thread factory}.
*
* @param corePoolSize the number of threads to keep in the pool, even
@ -2081,7 +2088,20 @@ public class ThreadPoolExecutor extends AbstractExecutorService {
/**
* A handler for rejected tasks that discards the oldest unhandled
* request and then retries {@code execute}, unless the executor
* is shut down, in which case the task is discarded.
* is shut down, in which case the task is discarded. This policy is
* rarely useful in cases where other threads may be waiting for
* tasks to terminate, or failures must be recorded. Instead consider
* using a handler of the form:
* <pre> {@code
* new RejectedExecutionHandler() {
* public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
* Runnable dropped = e.getQueue().poll();
* if (dropped instanceof Future<?>) {
* ((Future<?>)dropped).cancel(false);
* // also consider logging the failure
* }
* e.execute(r); // retry
* }}}</pre>
*/
public static class DiscardOldestPolicy implements RejectedExecutionHandler {
/**