#5897: GHC runtime task workers are not released with C FFI
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Reporter: sanketr | Owner:
Type: bug | Status: new
Priority: highest | Milestone: 7.4.2
Component: Runtime System | Version: 7.4.1
Resolution: | Keywords: worker, ffi
Os: Unknown/Multiple | Architecture: x86_64 (amd64)
Failure: None/Unknown | Difficulty: Unknown
Testcase: | Blockedby:
Blocking: | Related: #4262
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Comment(by sanketr):
Sorry, comment system mangled the steps. Here it is again:
In case it is not clear right away from the code, here is the sequence of
execution from timerevent when forking FFI threads:
{{{
- timerevent forks sendSignal threads - it forks n threads corresponding
to n C FFI threads
- timerevent now waits on a list of mvar m2 - list has n elements, one
corresponding to each sendSignal thread
- each sendSignal thread calls back syncWithC function - puts an element
in m2, and waits on m1
- timerevent gets all m2, and puts 0 in list of m1
- Each syncWithC thread (which was called back by sendSignal) gets its
corresponding m1, and finishes.
sendSignal is done. Those FFI threads are now finished.
}}}
So, if sendSignal is finished (otherwise the code will deadlock if mvars
are not put/taken in right order), the number of worker threads shouldn't
keep increasing with each iteration of timerevent.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5897#comment:10>
GHC <http://www.haskell.org/ghc/>
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