(PHP 4 >= 4.1.0, PHP 5, PHP 7)
Waits on or returns the status of a forked child
int pcntl_waitpid ( int $pid, int &$status [, int $options = 0 ] )
Suspends execution of the current process until a child as specified by the pid argument has exited, or until a signal is delivered whose action is to terminate the current process or to call a signal handling function.
If a child as requested by pid has already exited b