[GHC] #2233: Overhaul System.Process

[GHC]

#2233: Overhaul System.Process
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        Reporter:  simonmar           |            Owner:  simonmar
            Type:  task               |           Status:  patch
        Priority:  normal             |        Milestone:  _|_
       Component:  libraries/process  |          Version:  6.8.2
      Resolution:                     |         Keywords:
Operating System:  Unknown/Multiple   |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown       |       Difficulty:  Unknown
       Test Case:                     |       Blocked By:
        Blocking:                     |  Related Tickets:
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Comment (by Herbert Valerio Riedel <hvr@…>):

 In [changeset:"d95a67012ea30b02144d193254d947cdf5400a9d/process"]:
 {{{
 #!CommitTicketReference repository="process"
 revision="d95a67012ea30b02144d193254d947cdf5400a9d"
 Be even more careful with the threads that consume output (#2233)

 There is a potential deadlock with withCreateProcess in the case that
 there's an exception: cleanupProcess will try to hClose the various
 handles, but if another thread holds the Handle lock then that hClose
 will block.

 Takano Akio fixed the main case of this (in patch
 32223a9ab174c22e939c81e24b6f48223c7cb020) by terminating the process
 (before closing the handles) This works because terminating the process
 will eventually cause those other threads to finish and release the
 Handle lock, so we can hClose.

 However on Unix terminateProcess is not guaranteed to terminate the
 process since it uses SIGTERM, which can be handled or ignored. So we
 have to separately guarantee that the handles can be hClosed, and the
 simplest way to do this is to ensure that the thread reading from the
 handles get killed in the case there's an exception.

 So we change forkWait to withForkWait that will kill off the thread if
 the body gets an exception.

 Authored-by: Duncan Coutts <duncan at well-typed.com>
 Signed-off-by: Herbert Valerio Riedel <hvr at gnu.org>
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2233#comment:26>
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