PID process check

This class can check if a PHP script is running using PID files.

It looks at a given directory to see if it exists a process identifier file with the number of the current script process.

If the file exists, the class can call a Windows COM object or send a POSIX signal under a Linux/Unix system to determine if a process is running.

If the script is not yet running, the class creates the PID file and stores process number in it.