a22d4ba859
Motivation The epoll transport was updated in #7834 to decouple setting of the timerFd from the event loop, so that scheduling delayed tasks does not require waking up epoll_wait. To achieve this, new overridable hooks were added in the AbstractScheduledEventExecutor and SingleThreadEventExecutor superclasses. However, the minimumDelayScheduledTaskRemoved hook has no current purpose and I can't envisage a _practical_ need for it. Removing it would reduce complexity and avoid supporting this specific API indefinitely. We can add something similar later if needed but the opposite is not true. There also isn't a _nice_ way to use the abstractions for wakeup-avoidance optimizations in other EventLoops that don't have a decoupled timer. This PR replaces executeScheduledRunnable and wakesUpForScheduledRunnable with two new methods before/afterFutureTaskScheduled that have slightly different semantics: - They only apply to additions; given the current internals there's no practical use for removals - They allow per-submission wakeup decisions via a boolean return val, which makes them easier to exploit from other existing EL impls (e.g. NIO/KQueue) - They are subjectively "cleaner", taking just the deadline parameter and not exposing Runnables - For current EL/queue impls, only the "after" hook is really needed, but specialized blocking queue impls can conditionally wake on task submission (I have one lined up) Also included are further optimization/simplification/fixes to the timerFd manipulation logic. Modifications - Remove AbstractScheduledEventExecutor#minimumDelayScheduledTaskRemoved() and supporting methods - Uplift NonWakeupRunnable and corresponding default wakesUpForTask() impl from SingleThreadEventLoop to SingleThreadEventExecutor - Change executeScheduledRunnable() to be package-private, and have a final impl in SingleThreadEventExecutor which triggers new overridable hooks before/afterFutureTaskScheduled() - Remove unnecessary use of bookend tasks while draining the task queue - Use new hooks to add simpler wake-up avoidance optimization to NioEventLoop (primarily to demonstrate utility/simplicity) - Reinstate removed EpollTest class In EpollEventLoop: - Refactor to use only the new afterFutureTaskScheduled() hook for updating timerFd - Fix setTimerFd race condition using a monitor - Set nextDeadlineNanos to a negative value while the EL is awake and use this to block timer changes from outside the EL. Restore the known-set value prior to sleeping, updating timerFd first if necessary - Don't read from timerFd when processing expiry event Result - Cleaner API for integrating with different EL/queue timing impls - Fixed race condition to avoid missing scheduled wakeups - Eliminate unnecessary timerFd updates while EL is awake, and unnecessary expired timerFd reads - Avoid unnecessary scheduled-task wakeups when using NIO transport I did not yet further explore the suggestion of using TFD_TIMER_ABSTIME for the timerFd. |
||
|---|---|---|
| .. | ||
| src | ||
| pom.xml | ||
| README.md | ||
Native transport for Linux
See our wiki page.