#5553: sendWakeup error in simple test program with MVars and killThread -------------------------------------+------------------------------------- Reporter: bit | Owner: (none) Type: bug | Status: closed Priority: high | Milestone: 8.2.2 Component: Runtime System | Version: 8.0.1 Resolution: fixed | Keywords: Operating System: Linux | Architecture: x86 Type of failure: Incorrect result | Test Case: at runtime | Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by dfeuer): * status: new => closed * resolution: => fixed Comment: I'm unable to reproduce this in 8.2.1. I think it may have been fixed by d5cd505bc484edee3dbd5d41fb7a27c2e18d528d {{{ Author: Ben Gamari <bgamari.foss@gmail.com> Date: Tue Jan 17 15:52:37 2017 -0500 event manager: Don't worry if attempt to wake dead manager fails This fixes #12038, where the TimerManager would attempt to wake up a manager that was already dead, resulting in setnumcapabilities001 occassionally failing during shutdown with unexpected output on stderr. I'm frankly still not entirely confident in this solution but perhaps it will help to get a few more eyes on this. My hypothesis is that the TimerManager is racing: thread TimerManager worker ------- -------------------- requests that thread manager shuts down begins to clean up, closing eventfd calls wakeManager, which tries to write to closed eventfd To prevent this `wakeManager` will need to synchronize with the TimerManger worker to ensure that the worker doesn't clean up the `Control` while another thread is trying to send a wakeup. However, this would add a bit of overhead on every timer interaction, which feels rather costly for what is really a problem only at shutdown. Moreover, it seems that the event manager (e.g. `GHC.Event.Manager`) is also afflicted by a similar race. This patch instead simply tries to catch the write failure after it has happened and silence it in the case that the fd has vanished. It feels rather hacky but it seems to work. Test Plan: Run `setnumcapabilities001` repeatedly Reviewers: hvr, austin, simonmar Subscribers: thomie Differential Revision: https://phabricator.haskell.org/D2957 GHC Trac Issues: #12038 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5553#comment:14> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler