The pcntl_waitpid() function 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 by the time of the call (a so-called "zombie" process), the function returns immediately. Any system resources used by the child are freed. Please see your system's waitpid(2) man page for specific details as to how waitpid works on your system.
pcntl_waitpid() returns the process ID of the child which exited, -1 on error or zero if WNOHANG was used and no child was available
The value of pid can be one of the following:
Table 1. possible values for pid
| < -1 | wait for any child process whose process group ID is equal to the absolute value of pid. |
| -1 | wait for any child process; this is the same behaviour that the wait function exhibits. |
| 0 | wait for any child process whose process group ID is equal to that of the calling process. |
| > 0 | wait for the child whose process ID is equal to the value of pid. |
pcntl_waitpid() will store status information in the status parameter which can be evaluated using the following functions: pcntl_wifexited(), pcntl_wifstopped(), pcntl_wifsignaled(), pcntl_wexitstatus(), pcntl_wtermsig() and pcntl_wstopsig().
The value of options is the value of zero or more of the following two global constants OR'ed together:
Table 2. possible values for options
| WNOHANG | return immediately if no child has exited. |
| WUNTRACED | return for children which are stopped, and whose status has not been reported. |
See also pcntl_fork(), pcntl_signal(), pcntl_wifexited(), pcntl_wifstopped(), pcntl_wifsignaled(), pcntl_wexitstatus(), pcntl_wtermsig() and pcntl_wstopsig().