Re^6: How to tell a child what to do?

in reply to Re^5: How to tell a child what to do?
in thread How to tell a child what to do?

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.

Comment on Re^6: How to tell a child what to do?

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Re^7: How to tell a child what to do? by Eyck (Priest) on Sep 23, 2005 at 07:07 UTC
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.	[reply] [d/l] [select]

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Re^7: How to tell a child what to do?
by Eyck (Priest) on Sep 23, 2005 at 07:07 UTC

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]

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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