[GHC] #9377: forkProcess unnecessarily sets wait_foreign in hs_exit_

29 Jul 2014

      #9377: forkProcess unnecessarily sets wait_foreign in hs_exit_
-------------------------------------+-------------------------------------
       Reporter:  edsko              |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Unknown            |         Type of failure:
     Blocked By:                     |  None/Unknown
Related Tickets:                     |               Test Case:
                                     |                Blocking:
                                     |  Differential Revisions:  Phab:D99
-------------------------------------+-------------------------------------
 During normal course of action in `real_main` a process is terminated with
 a call to

 {{{#!hs
     shutdownHaskellAndExit(exit_status, 0 /* !fastExit */);
 }}}

 which is defined as

 {{{#!hs
 void shutdownHaskellAndExit(int n, int fastExit)
 {
     if (!fastExit) {
         // even if hs_init_count > 1, we still want to shut down the RTS
         // and exit immediately (see #5402)
         hs_init_count = 1;

         // we're about to exit(), no need to wait for foreign calls to
 return.
         hs_exit_(rtsFalse);
     }

     stg_exit(n);
 }
 }}}

 However, when we call `forkProcess`, the child process does ''not''
 terminate in this manner, but instead calls

 {{{#!hs
        hs_exit();                      // clean up and exit
        stg_exit(EXIT_SUCCESS);
 }}}

 instead, where `hs_exit` is defined as

 {{{#!hs
 void hs_exit(void)
 {
     hs_exit_(rtsTrue);
     // be safe; this might be a DLL
 }
 }}}

 Crucially, this means that, unlike the parent, the child process ''does''
 wait for foreign calls to be terminated (it calls `hs_exit_` with
 `rtsTrue` instead of `rtsFalse`).

 I don't see a reason why the child process should terminate in a different
 manner to the parent, so I propose to change this so that `forkProcess`
 calls `shutdownHaskellAndExit`, just like `real_main` does.

 Incidentally, this is the immediate cause for
 https://ghc.haskell.org/trac/ghc/ticket/9284 , although the patch proposed
 in this ticket is not sufficient to solve the problems with termination of
 the I/O manager in the general case (but I will let Andreas explain that
 in more detail :).

--
Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9377
GHC http://www.haskell.org/ghc/
The Glasgow Haskell Compiler