sigCHLD signal handling (Was: Re: pipes? threadWaitRead?)

[Dean Herington]

After much study I have a new theory.  It appears that the pipe machinery
is working fine, but that sometimes my program fails to "reap" all of its
terminated child processes.  I'm using a `sigCHLD` signal handler that
does `getAnyProcessStatus True False` each time it's invoked.  It seems
that one or more `sigCHLD` signals are occurring while an instance of the
handler is already running (having presumably blocked `sigCHLD` during its
execution), and hence the "contemporaneous" signals are getting lost.
(Oh, and it seems this unfortunate behavior occurs for me under Linux but
not Solaris.)

How can I avoid losing `sigCHLD` signals?

It seems that use of the `SA_NODEFER` flag on `sigaction` might do the
trick, but that flag is not accessible via `installHandler`.

Dean


On Mon, 8 Jul 2002, Dean Herington wrote:

> I have some GHC-compiled programs that run OK under Sparc/Solaris but
> hang under x86/Linux.  I'm using GHC 5.02.3 on both systems (although
> I've tried GHC 5.03.20020410 on Linux with the same failures).  I'm
> debugging to narrow the problem down.  My current suspicion is that
> closing the write end of a pipe is not always causing the read end to
> see end-of-file.  Is there any strangeness relating to this--or perhaps
> with `threadWaitRead` on pipes--that anyone knows about?  I sometimes
> use a pipe to have two GHC threads communicate within a single process.