Fixed Timer tasks being run after cancellation. #7393
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I deployed this to production for Spine (YOLO) and found when a task is run it could modify |
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A few thousand Spine users have tested it, seems OK! |
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Timer considers a task "executed" when the timer thread posts it via
Gdx.app.postRunnable. Code on the app thread may cancel a task that has been posted but not executed yet. It is then very confusing for the app to see a taskrunafter it has been cancelled. To be safe, app code needs to check state for every task execution to make sure it is valid. This can be difficult, eg if a task is cancelled and rescheduled, the app could see both the cancelled and rescheduled execution.We need a way for Timer to post runnables but still be able to remove them before they execute, if needed. This PR does that by having the timer post a single runnable
runPostedTaskswhenever there are one or more tasks that need to be executed.runPostedTasksthen executes each task inArray<Task> postedTasks. When a task is cancelled, it is removed frompostedTasks, solving the "executed after cancel" problem. From the app code perspective, everything should work as it did before.postedTasksis stored in TimerThread (ie globally) rather than Timer because once a task is no longer scheduled to execute in the future, Taskresetis called andtimerset to null. It no longer knows about the timer, so wouldn't be able to remove itself frompostedTaskson the timer.New synchronization was added around
postedTasks, which is synchronized when running tasks. That means a timer posting a new task must wait while all thepostedTasksexecute. This is probably OK, as tasks aren't generally long running and a newly added task won't be serviced until next frame anyway. If it were important, we could do like the LWJGL backends that useArray<Runnable> runnables, executedRunnables, synchronizing only long enough to copy the tasks that will run.This PR also adds more lovely Timer tests.