Discussions on php-dev in the middle of 2002, indicated that Brad LaFountian and Shane Caraveo had discussed this at OSCON. Came to light after my first attempt at trying to implement it.. First effort involved threading the zend_execute call Had big problems ('thrashing locks') Implementing Threading closely related to the internal design of the Zend engine Bytecodes can not be shared as they are not static PHP has support for multithreading and managing memory for multiple threads PHP is more like perl than Python internally (Python does queued opcode execution)