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in reply to Re^4: How to tell a child what to do?
in thread How to tell a child what to do?

Great. This is perfect.

However, I don't know why my version fails, which worries me.

Thanks again, I've got enough to tinker with now.

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Re^6: How to tell a child what to do?
by Anonymous Monk on Sep 21, 2005 at 12:25 UTC
    I've played with the code a bit more, and it's failing for me as well. But not always. How often it fails, depends on the number of spawned children. Trying 1, 2, 3, 4, and 5 children, each 10 times, I get success rates of 100%, 90%, 40%, 10% and 0%.

    Something is wrong, but I do not know what. I'll have to consult Stevens.

[reply]
      I think, that if you rewrite this with sysread/syswrite, or, like in merlyn's solution with length-based communication, it starts working.

      This may have something to do with perl's buffering, in particular, when instead of while (<>) I wrote this: 

              my $q;
        $q=<STDIN>;
        print "Received(child $$): $q\n";

      [download]
      it stopped hanging on close($fd).

      When I traced what is happening when it hangs, it looks like parent is waiting waitpid(..) (close($fd) on pipe is supposed to do that), while child blissfully unaware is running read...

      Now I can safely go and try to understand merlyn's code.

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