php man page for pcntl_waitpid

PCNTL_WAITPID(3)							 1							  PCNTL_WAITPID(3)

pcntl_waitpid - Waits on or returns the status of a forked child

SYNOPSIS
       int pcntl_waitpid (int  $pid, int  &$status, [int  $options])

DESCRIPTION
	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  immedi-
       ately.  Any system resources used by the child are freed. Please see your system's waitpid(2) man page for specific details as to how wait-
       pid works on your system.

PARAMETERS
	      o $pid
		- The value of $pid can be one of the following:

	      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 be- |
	      |     | haviour 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.				|
	      |     |							|
	      +-----+---------------------------------------------------+
	      Note

		      Specifying -1 as the $pid is equivalent to the functionality pcntl_wait(3) provides (minus $options).

	      o $status
		-pcntl_waitpid(3) will store status information in the $status parameter which can be evaluated  using	the  following	functions:
		pcntl_wifexited(3), pcntl_wifstopped(3), pcntl_wifsignaled(3), pcntl_wexitstatus(3), pcntl_wtermsig(3) and pcntl_wstopsig(3).

	      o $options
		- The value of $options is the value of zero or more of the following two global constants OR'ed together:

	      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.		     |
	      | 	 |						     |
	      +----------+---------------------------------------------------+
RETURN VALUES
       pcntl_waitpid(3) returns the process ID of the child which exited, -1 on error or zero if WNOHANG was used and no child was available

SEE ALSO
       pcntl_fork(3), pcntl_signal(3), pcntl_wifexited(3),  pcntl_wifstopped(3),  pcntl_wifsignaled(3),  pcntl_wexitstatus(3),	pcntl_wtermsig(3),
       pcntl_wstopsig(3).

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