in reply to Waitpid does not work as expected in Windows

Remember that fork creates threads that look like processes (rather than actual processes) on Windows.

use Win32::OLE('in');

It works fine when I remove this. Do you have any reason to believe it's thread-safe?

if ($check > 0)

The pseudo-processes created by fork on Windows have negative PIDs. That should be if ($check != -1).

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Re^2: Waitpid does not work as expected in Windows
by athanasia (Pilgrim) on Sep 29, 2008 at 11:33 UTC
    Thanks for your reply!
    I did not know that pids in Windows were negative.

    Also, your suggestion about removing
    use Win32::OLE('in');
    solved the problem. Unfortunately, I need this module because the code snippet I posted is part of a larger project that needs Win32::OLE->GetObject function. Do you know what causes this incompatibility? Is there a way in Perl to use a module for a part of the program and disable it for the rest rather than defining it in a global scope?

    Thanks in advance
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      I did not know that pids in Windows were negative.

      They're not. That's why negative numbers were used to id the pseudo-processes created by fork.

      Do you know what causes this incompatibility?

      The usual possibilities:

      • A race condition. Not very likely here considering the simplicity of the code and the repeatability of the problem.
      • Something that should only be called once is being called once for each thread.
      • Something is called from one thread but expects to be called from another.

      On the Perl side, every variable gets copied when you create a new thread. That makes Perl code more-or-less thread-safe by default. But that's not the case on the C component of XS modules. C variables are shared among threads "by default".

      Workarounds:

      • If you only need Win32::OLE in the parent, you could try loading it after all threads have been created. This will probably entail using require instead of use.
      • If you only need Win32::OLE in the child, you could try loading it from the thread. This will probably entail using require instead of use.
      • If you need Win32::OLE in both the parent and the child, it probably won't work based on the evidence we've seen. Using separate processes would do the trick.
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        Your suggestion to require the module instead of 'using' it did the work. Thanks a lot for all the useful info and help!
        Athanasia
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