I'm writing a small application using React and Ratchet that opens up a few long-running external processes, and redirects some of their output (via stdout) through a websocket connection.

Using popen and React's stream class to talk to the external process usually works just fine, and the process's output gets sent to the websocket as it executes -- as one would expect. Some processes, however, block the event loop until they've completed running.

Inside my Ratchet application, I can run

$ping = new Stream(popen("ping -t 127.0.0.1",'r'),$server->loop);
$ping->on('data',function($data) use ($from){
    $from->send($data);
});

and ping will continuously direct its output through my websocket connection, $from.

However, if I use a different executable (in this case, the Adobe F4V Post-Processor), I get no output from f4vpp, or anything else in my event loop (say, the ping command above) until f4vpp exits.

$f4vpp = new Stream(popen("f4vpp -v -i in.f4v -o out.mp4",'r'),$server->loop);
$f4vpp->on('data',function($data) use ($from){
    $from->send($data);
});

What's going on here? Is this user error, or a legitimate shortcoming in React or PHP on win32?