[GHC] #4362: error in multithreaded program "epollControl: does not exist (No such file or directory)"

[GHC]

#4362: error in multithreaded program "epollControl: does not exist (No such file
or directory)"
------------------------------------------+---------------------------------
  Reporter:  guest                        |          Owner:       
      Type:  bug                          |         Status:  new  
  Priority:  normal                       |      Milestone:  7.0.2
 Component:  libraries/base               |        Version:  7.1  
Resolution:                               |       Keywords:       
  Testcase:                               |      Blockedby:       
Difficulty:                               |             Os:  Linux
  Blocking:                               |   Architecture:  x86  
   Failure:  Incorrect result at runtime  |  
------------------------------------------+---------------------------------

Comment(by dleuschner):

 I can't really say anything about epoll because I just looked at it today
 but I noticed a thing while looking at the strace output of the program
 Stefan posted.  I seems that epoll discards watched file descriptors when
 they are closed but the IO manager seems to think that the file descriptor
 is still registered with epoll.  I extracted the following sequence
 concerning file descriptors with index 7:

 {{{
 [pid 27110] accept(12, {sa_family=AF_INET, sin_port=htons(39725),
 sin_addr=inet_addr("127.0.0.1")}, [16]) = 7
 [pid 27112] epoll_ctl(3, EPOLL_CTL_ADD, 7, {EPOLLIN, {u32=7,
 u64=2392000568567529479}}) = 0
 [pid 27112] close(7)                    = 0
 [pid 27111] socket(PF_INET, SOCK_STREAM, IPPROTO_IP) = 7
 [pid 27111] <... read resumed> "127.0.0.1\tlocalhost\n178.63.197.6"...,
 4096) = 70
 [pid 27111] epoll_ctl(3, EPOLL_CTL_MOD, 7, {EPOLLIN|EPOLLOUT, {u32=7,
 u64=21500846801944583}}) = -1 ENOENT (No such file or directory)
 }}}

 In the last line the IO manager seems to assume that file descriptor 7 is
 still registered with epoll because it was added in line 2 but probably
 the close in line 3 invalidate or removed the file descriptor.  I have
 written a tiny C testprogram that demonstrates that the "socket -> N",
 "epoll_ctl add N", "close N", "socket -> N", "epoll_ctl modify N" sequence
 doesn't work.  Maybe that bit of information is helpful.  You can find the
 full strace and Haskell log for the run in ~/ghc-bug/server.trace on our
 system.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4362#comment:14>
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