On Wed, 19 Feb 2025 16:07:56 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 should wait for dela...
src/java.base/share/classes/java/util/concurrent/ForkJoinPool.java line 3720: > 3718: /** > 3719: * Submits a task executing the given function, cancelling or > 3720: * performing a given timeoutAction if not completed within the "cancelling or performance a given timeoutAction" could be misread to mean that it cancels the timeoutAction. It might be clear to say "cancelling the task or ...". ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/23702#discussion_r1964057274
