#9295: Deadlock in forkProcess ------------------------------------+------------------------------------- Reporter: edsko | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- As part of `forkProcess` we discard all tasks except the one task that remains. As part of this we call `freeTask`, and `freeTask` in turn calls `closeCondition` and `closeMutex`, which are very thin wrappers around `pthread_cond_destroy` and `phread_mutex_destroy`. However, the behaviour of these functions is undefined when there are currently threads blocked on these condition variables/mutexes. In reality, this undefined behaviour often (though not always) results in a deadlock. Unfortunately, I don't have a minimal test case to demonstrate this, but in the large system on which I am testing this I am seeing these deadlocks rather frequently. For the global mutex we don't attempt to call `pthread_cond_destroy` or `pthread_mutex_destroy`, but instead re-initialize them. The patch https://phabricator.haskell.org/D59 does precisely that for the condition variables and mutexes associated with tasks. This is ''somewhat'' or a long way around, because we will then subsequently still call `pthread_..._destroy`, but it means that we don't have to mess with `freeTask`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9295 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler