PHP wrapper script streaming stdout & stderr in parallel

PHP proces wrapper

<?php
// microsecond timeout
$timeout = 1000;

// launch proces, retrieve output & error streams
$proc=proc_open($cmd,array(0=>array('pipe','r'),1=>array('pipe','w'),2=>array('pipe','w')), $streams);
$stdOut = $streams[1];
$stdErr = $streams[2];

while($stdOut || $stdErr){
    $streams = array();

    // only read from open streams
    if ($stdOut)
        $streams[] = $stdOut;
    if ($stdErr)
        $streams[] = $stdErr;

    // check if there are any streams left to read from
    if (empty($streams)) break;

    // wait for output from open streams
    if (false !== stream_select($streams, $write=null, $expect=null, 0, $timeout)) {

        // $streams now contains available streams
        foreach($streams as $stream) {
            if($stream == $stdOut) {
                // read one line from output stream
                $line = fgets($stdOut );

                if (trim($line))
                    echo "Out: $line";

                if (feof($stdOut)) {
                    echo "Closing output stream\n";
                    fclose($stdOut);
                    $stdOut = null;
                }
            }

            if($stream == $stdErr) {
                // read one line from error stream
                $line = fgets($stdErr);

                if (trim($line))
                    echo "Error: $line";

                if (feof($stdErr))  {
                    echo "Closing error stream\n";
                    fclose($stdErr);
                    $stdErr = null;
                }
            }
        }
    }
}