Fix spurious wake-ups and worker threads initialization in workerpool #339
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Thanks for the PR. I approved the CI for this PR. The tests crash on Windows ( |
I was able to reproduce on a Windows machine 😄 It turns out that the |
added 2 commits
June 26, 2024 10:16
Threads that wait on the condition variable startcond can be woken up spuriously. This is not a problem if no tasks have been added, but as soon as there is one, the condition in the while loop of worker_thread will evaluate to false and the worker thread will run the task. If more tasks are added, there is a chance that the zarray is reallocated and that its pointer is changed. Since the woker thread gets a raw pointer to the zarray, this pointer can become invalid and cause a segfault. The solution is to add a predicate that is checked when the worker thread is woken up on the condition variable startcond. The while loop now has 2 conditions: - start condition: if wp->start_tasks is true, tasks can be executed - stop condition: if wp->taskspos == zarray_size(wp->tasks), there are no more tasks to execute I also shielded concurrent accesses to the pointer wp with the mutex.
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christian-rauch
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Jun 26, 2024
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Thanks a lot! |
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I encountered random segfaults while using this library and tried to figure out what was happening. I isolated the segfault to the function
worker_thread()ofworkerpool.c. Long story short, there is no predicate that preventsworker_thread()from running if it is woken up spuriously and a task has already been added. Since there is no mutex used inworkerpool_add_task(), it is possible for the zarraywp->tasksto be reallocated, rendering the volatile pointertaskinworker_thread()invalid and causing a segfault.This PR addresses this issue by adding a predicate and shielding calls that access
wpbehind a mutex. I also saw issue #70 and agree that the initialization of the worker threads might lead to race conditions, so I addressed that too.