On Tue, 25 Mar 2025 19:57:54 GMT, Doug Lea <d...@openjdk.org> wrote:
>> (Copied from https://bugs.openjdk.org/browse/JDK-8319447)
>>
>> The problems addressed by this CR/PR are that ScheduledThreadPoolExecutor is
>> both ill-suited for many (if not most) of its applications, and is a
>> performance bottleneck (as seen especially in Loom and CompletableFuture
>> usages). After considering many options over the years, the approach taken
>> here is to connect (lazily, only if used) a form of ScheduledExecutorService
>> (DelayScheduler) to any ForkJoinPool (including the commonPool), which can
>> then use more efficient and scalable techniques to request and trigger
>> delayed actions, periodic actions, and cancellations, as well as coordinate
>> shutdown and termination mechanics (see the internal documentation in
>> DelayScheduler.java for algotihmic details). This speeds up some Loom
>> operations by almost an order of magnitude (and similarly for
>> CompletableFuture). Further incremental improvements may be possible, but
>> delay scheduling overhead is now unlikely to be a common performance concern.
>>
>> We also introduce method submitWithTimeout to schedule a timeout that
>> cancels or otherwise completes a submitted task that takes too long. Support
>> for this very common usage was missing from the ScheduledExecutorService
>> API, and workarounds that users have tried are wasteful, often leaky, and
>> error-prone. This cannot be added to the ScheduledExecutorService interface
>> because it relies on ForkJoinTask methods (such as completeExceptionally) to
>> be available in user-supplied timeout actions. The need to allow a pluggable
>> handler reflects experience with the similar CompletableFuture.orTimeout,
>> which users have found not to be flexible enough, so might be subject of
>> future improvements.
>>
>> A DelayScheduler is optionally (on first use of a scheduling method)
>> constructed and started as part of a ForkJoinPool, not any other kind of
>> ExecutorService. It doesn't make sense to do so with the other j.u.c pool
>> implementation ThreadPoolExecutor. ScheduledThreadPoolExecutor already
>> extends it in incompatible ways (which is why we can't just improve or
>> replace STPE internals). However, as discussed in internal documentation,
>> the implementation isolates calls and callbacks in a way that could be
>> extracted out into (package-private) interfaces if another j.u.c pool type
>> is introduced.
>>
>> Only one of the policy controls in ScheduledThreadPoolExecutor applies to
>> ForkJoinPools with DelaySchedulers: new method cancelDelayedTasksOnShutdown
>> controls whether quiescent shutdown sh...
>
> Doug Lea has updated the pull request with a new target base due to a merge
> or a rebase. The pull request now contains 49 commits:
>
> - Merge branch 'openjdk:master' into JDK-8319447
> - Address review comments
> - Merge branch 'openjdk:master' into JDK-8319447
> - Match indent of naster changes
> - Use TC_MASK in accord with https://bugs.openjdk.org/browse/JDK-8330017
> (Unnecessarily for now.)
> - Reword javadoc
> - Use SharedSecrets for ThreadLocalRandomProbe; other tweaks
> - Disambiguate caller-runs vs Interruptible
> - Merge branch 'openjdk:master' into JDK-8319447
> - Associate probes with carriers if Virtual (no doc updates yet)
> - ... and 39 more: https://git.openjdk.org/jdk/compare/dbc620fb...4aabe6b0
src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 3743:
> 3741: * @since 25
> 3742: */
> 3743: public void cancelDelayedTasksOnShutdown() {
@DougLea Should this really be possible to enable for the common pool? (Because
different parts of an application using commonPool() could have conflicting
requirements)
src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 3927:
> 3925: * periodic) tasks scheduled in this pool that are not yet ready
> 3926: * to submit for execution. The returned value is innacurate when
> 3927: * delayed tasks are being processed.
Suggestion:
* to submit for execution. The returned value is innacurate while
* delayed tasks are being processed.
src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 3932:
> 3930: * @since 25
> 3931: */
> 3932: public int getDelayedTaskCount() {
@DougLea It would seem more consistent to have this return a `long` like
`getQueuedTaskCount` (even if that amount isn't currently possible to represent
in the heap. Thoughts, @AlanBateman?
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r2014113345
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r2014115483
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r2014118038
