The following program usually hangs for me when I run it on Windows. 

use strict;
use warnings;
use threads;

$|=1;

my $niter  = 10;
# Seems to mostly work with $nforks = 2 but usually fails with $nforks
+ = 3.
my $nforks = 3;
my $Cmd = 'invalid_command';

warn "start niter=$niter nforks=$nforks cmd='$Cmd'\n";

sub do_one_kid {
   my $kid = shift;
   warn "kid $kid pid=$$ run cmd='$Cmd'\n";
   for my $i (1..$niter) {
      my $out = `$Cmd 2>&1`;
      my $rc = $? >> 8;
      warn "$i: kid $kid pid=$$ rc=$rc\n";
   }
   warn "kid $kid pid=$$ exit\n";
   return 42;
}

my @kids = ();
for my $n (1..$nforks)
{
   warn "$n: forking\n";
   my $t = threads->new(\&do_one_kid, $n);
   warn "I am the parent\n";
   push(@kids, $t);
}

for my $t (@kids) {
   warn "parent waiting\n";
   my $rc = $t->join();
   warn "parent $$: thread exited rc=$rc\n";
}

warn "end main\n";

[download]

I've got a patch to win32.c to fix the hang nearly ready. However, before submitting it to P5P, I thought it would be best if I also included a test in the patch.

Though I can write a test based on the above program easily enough, this test will hang when it fails ... which is less than desirable.

Grovelling through the tests that come with Perl, I noticed that the fresh_perl_is() function in t/test.pl seems to be used for tests that crash perl. But what about tests that don't crash perl but may cause it to hang forever? Is there a recommended way to write these types of tests?

Update 21-sep-2006: This bug has now been fixed (change #28873) in the Perl core in file win32/win32.c. Related links:

In reply to How to write a test for backticks threads hang by eyepopslikeamosquito

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