php-shellcommand: PHP hanging indefinitely

I was testing some html conversions using the mikehaertl/phpwkhtmltopdf, when I noticed one made PHP hang indefinitely.

Doing some debug, I found out that it was happening in the php-shellcommand/src/Command.php file at line number 317:

$this->_stdOut = stream_get_contents($pipes[1]); 

After some research, I found a similar problem in this stackoverflow question and an apparent solution. http://stackoverflow.com/questions/31194152/proc-open-hangs-when-trying-to-read-from-a-stream

According to the stackoverflow answer, there is a possibility of an execution not outputting anything to stdout (pipe[1]) when an error occurs, so stream_get_contents waits for a stream that never comes.

As pointed out in the stackoverflow answer, reading the stderr (pipe[2]) before stdout (pipe[1]) did the trick for me, with the PHP finishing execution and the error message being outputted.

$this->_stdErr = stream_get_contents($pipes[2]);
$this->_stdOut = stream_get_contents($pipes[1]); 

My system config:

• Ubuntu 14.04.1 LTS running as a headless VM on Virutalbox
• PHP Version 5.5.22-1+deb.sury.org~trusty+1
• Apache/2.4.12
• wkhtmltopdf 0.12.2 (with patched qt)