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Re^3: IPC::Open3 woes

by ikegami (Pope)
on Apr 21, 2010 at 23:36 UTC ( #836165=note: print w/ replies, xml ) Need Help??


in reply to Re^2: IPC::Open3 woes
in thread IPC::Open3 woes

I am hopeing that somebody can add some clarity to this old thread. Can somebody tell me why the following coded hangs if the line which defines the @outlines array is commented out?

You have a deadlock.

  • waitpid never returns because the child never exits.
  • The child never exits because it's blocked trying to write a full pipe.
  • The pipe is full because noone is emptying it.

If it doesn't happen for all your children, it's because they don't output enough data to fill the pipe.

use strict; use warnings; use IPC::Open3 qw( open3 ); for (my $size = 1024; ; $size += 1024) { print("$size\n"); my $pid = open3( local our $to_chld, local our $fr_chld, local our $fr_chld_err, perl => ( -e => 'print "x" x $ARGV[0]', $size ) ); waitpid($pid, 0); }
... 62464 63488 64512 65536 66560 [hangs]^C

The solution is to redirect the output to /dev/null

use strict; use warnings; use IPC::Open3 qw( open3 ); open(local *DEVNULL, '>', '/dev/null') or die; for (my $size = 1024; ; $size += 1024) { print("$size\n"); my $pid = open3( local our $to_chld, '>&DEVNULL', '>&DEVNULL', perl => ( -e => 'print "x" x $ARGV[0]', $size ) ); waitpid($pid, 0); }
... 365568 366592 367616 368640 369664 370688 371712 372736 373760 374784 ...


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