I have a problem on win32 (64bit win 7, perl v5.20.2, active state), where threads->create() hangs.

I am looking for debug pointers.

The code launches two processes: Process (1) a background process, and process(2) is GDB, the gdb target talks to the background process via a socket, I am creating an automated sw test environment, I need to control, interact and capture output (stdout) from the processes.

I'm using IPC::Open3() to create both processes processes, like this: 

    # i,o,e are std in/out/err

    $p = open3( $i, $o, $e, @cmdline );
    $hr->{'alive'} = 1;
    $hr->{'pid'} = $p;
    $hr->{'stdout'}= $o;
    $hr->{'stdin'} = $i;
    $hr->{'stderr'} = $e;

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To process the stdout, I create a reader thread like this: 
 # The reader is given the hash reference, the 'o' 
 # indicates this is the 'stdout' reader 
 $hr->{'o_thread'} = threads->create( \&reader_thread, $hr, 'o' );

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The above works quite well when I run one sub process. It locks up (the create call does not return) if I have two sub processes.

My only means to Debug is via print() - tells me that the call to threads->create() does not return, and print statement I put before threads->create() occurs, the after does not. And the print statement I put at the entry to the reader_thread never happens,

To be clear, this works a few times then does not work again.

Any suggestions how to dig deeper and figure out what I am doing wrong. Often, I insert print statements into various PM modules, but - threads are not perl, they are native code.

The reader thread is quite simple: 

sub reader_thread {
    my ($hr,$who) = @_;
    
    my $c;
    my $h;
    my $r;
    my $q;

    threads->detach();

    # determine handle.
    if( $who eq 'o' ){
    $h = $hr->{'stdout'};
    } else {
    $h = $hr->{'stderr'};
    }
    # Get the output queue
    $q = $hr->{'Q'};

    while( 1 ){
    if( $hr->{'alive'} == 0 ){
        last;
    }
    # Try to read *ONE* byte
    $r = read( $h, $c, 1 );
    if( $r > 0 ){
        if( length($c) ){
        $q->enqueue($c);
        }
    } else {
        threads->yield();
    }
    }
}

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In reply to threads->create hangs by duane_ellis2

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