On Fri, 21 Feb 2025 13:16:10 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 incrementally with one additional
> commit since the last revision:
>
> Address feedback
src/java.base/share/classes/java/util/concurrent/CompletableFuture.java line
2840:
> 2838: Canceller(Future<?> f) { this.f = f; }
> 2839: public void accept(Object ignore, Throwable ex) {
> 2840: if (f != null)
@DougLea Does it make sense to create a Canceller with a `null` `f`-parameter?
src/java.base/share/classes/java/util/concurrent/CompletableFuture.java line
2874:
> 2872: public static Executor delayedExecutor(long delay, TimeUnit unit,
> 2873: Executor executor) {
> 2874: return new DelayedExecutor(unit.toNanos(delay),
Suggestion:
return new DelayedExecutor(unit.toNanos(delay), // Implicit null-check
of unit
src/java.base/share/classes/java/util/concurrent/CompletableFuture.java line
2891:
> 2889: */
> 2890: public static Executor delayedExecutor(long delay, TimeUnit unit) {
> 2891: return new DelayedExecutor(unit.toNanos(delay), ASYNC_POOL);
Suggestion:
return new DelayedExecutor(unit.toNanos(delay), ASYNC_POOL); //
Implicit null-check of unit
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r1965819083
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r1965822241
PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r1965822660
