Re^3: IPC::Open3 woes

[ikegami]

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
...