I recently read about http://php.net/pcntl and was woundering how good that functions works and if it would be smart to use multithreading in PHP since it isn't a core function of PHP.
I would want to trigger events that don't require feedback through it like fireing a cronjob execution manually.
All of it is supposed to run in a web app written with Zend Framework
The pcntl package works quite fine - it just uses the according unix functions. The only shortage is that you can't use them if php is invoked from a web server context. i.e. you can use it in shell scripts, but not on web pages - at least not without using a hack like calling a forking script with exec or similar.
[edit] I just found a page explaining why mod_php cannot fork. Basically it's a security issue. [/edit]
The only possible way to have php code executing in multiple threads is to run php as a module of a threaded web server, which is useless because threads are fully isolated and your code has no control over them. As far as i know, pcntl only manages processes, not threads.
This is not thread control, this is process control. The library for the threads is pthreads (POSIX threads) and it's not included in PHP, so there are no multi-threading functions in PHP.
As of multiprocessing, you cannot use that in mod_php, as that would be a giant security hole (spawned process would have all the web-server's privileges).
If I needed to do manual crontab executions or the like from PHP, I'd probably use a queue. Have a database table that you append jobs to. Another process, either from a cron or running as a daemon, executes the jobs as they show up.
Another way to do it is to set up a separate script and do an HTTP GET to it. It's not quite threading, but it's one way of shelling to another command in PHP.
For example, if I wanted to run /usr/bin/somescript.sh on demand, I'd have a somescript.php that did a system call. This would be on a virtual host only accessible from localhost.
I'd do a socket call to the webserver and GET the script. The key is to not read on the socket so it doesn't block. If I wanted to check the return value of somescript.php, I'd do it later in my main script to prevent blocking.
If somescript.php takes a long time to execute (longer than the calling script), you'll have to do some magic to stop apache from killing the script when the socket is closed.
Multiplatform PHP Multithreading engine http://anton.vedeshin.com/articles/lightweight-and-multiplatform-php-multithreading-engine
Examples of multithreading working in PHP http://drupal.org/project/cron%5Fmt http://drupal.org/project/boost