[prelude][core][stm] fix issue with preemption in nested async computations #927
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fwbrasil
commented
Dec 13, 2024
| @@ -87,6 +87,9 @@ sealed private[kyo] class IOTask[Ctx, E, A] private ( | |||
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| private inline def nullResult = null.asInstanceOf[A < Ctx & Async & Abort[E]] | |||
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| override def toString = | |||
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to help with debugging
hearnadam
approved these changes
Dec 16, 2024
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Fixes #925
The issue is more generic than the use with STM. Kyo's kernel uses a safepoint mechanism to preempt execution on any step of a computation.
kyo-coreextends this mechanism by setting the safepoint interceptor to the current fiber to handle preemption. For example, if the fiber is interrupted, the next safepoint will trigger preemption to stop the computation and clear finalizers. The other possibility is the scheduler itself triggering preemption due to the fiber taking more than the configured time slice (10ms by default) so it can return to the execution queue to provide fairness.The cause of the bug is the interceptor propagating to nested async computations. This PR fixes
Safepoint.eval, which is called from the pending type'seval, to clear the interceptor since theevaloperation itself can't be delayed and has to return a concrete value. Even if the outer async computation is preempted, the nested one needs to execute to completion.