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[Chicken-users] Question about forks, pipes and sigchld handling

From: Peter Bex
Subject: [Chicken-users] Question about forks, pipes and sigchld handling
Date: Wed, 3 Oct 2012 18:21:45 +0200
User-agent: Mutt/

Hi all,

I'm trying to figure out the behavior of process-fork and the
handling of signal/chld (SIGCHLD).  Here's a simple program
which simply sets up a pipe and forks.  The parent process reads
from the pipe, the child writes to it.

(use posix)

#;(set-signal-handler! signal/chld void)

(receive (in out)
  (process-fork (lambda ()
                  (file-close in) ; close receiving end
                  (with-output-to-port (open-output-file* out)
                    (lambda ()
                      (display "hello, world\n")
                      ;; If we don't use exit, buffers are discarded by _exit
  (file-close out) ; close sending end
  (pp (read-lines (open-input-file* in))))

This program works just fine and prints ("hello, world").
If I uncomment the signal handler code (which should just be a no-op),
it hangs.  I don't understand the reason for this.  Could anyone
enlighten me as to what's happening here?

"The process of preparing programs for a digital computer
 is especially attractive, not only because it can be economically
 and scientifically rewarding, but also because it can be an aesthetic
 experience much like composing poetry or music."
                                                        -- Donald Knuth

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