PCNTL Functions
PHP Manual

pcntl_waitid

Waits for a child process to change state

Description

bool pcntl_waitid(
    int $idtype = P_ALL,
    intnull $id = null,
    array &$info = [],
    int $flags = WEXITED,
    array &$resource_usage = []
)

Obtains status information pertaining to termination, stop, and/or continue events in one of the caller's child processes.

Unless WNOHANG flag is passed, the calling process will become blocked until an error occurs, or status information becomes available that satisfies all of the following:

  • The status information is from one of the child processes in the set of child processes specified by the idtype and id arguments.
  • The state change in the status information matches one of the state change flags set in the flags argument.

If matching status information is available prior to the call to pcntl_waitid, return shall be immediate. If matching status information is available for two or more child processes, the order in which their status is reported is unspecified.

Note:

This documentation covers the POSIX specification of the waitid function, along with some additional parameters specific to implementations on Linux, NetBSD and FreeBSD. Please see your system's waitid(2) man page for specific details as to how waitid works on your system.

Parameters

idtype
id
The idtype and id arguments are used to specify which children to wait for.
POSIX standard idtype and id arguments
If idtype is P_ALL wait for any child process, id is ignored.
If idtype is P_PID wait for the child with process ID equal to id.
If idtype is P_PGID wait for any child with process group ID equal to id.
Linux specific idtype and id arguments
If idtype is P_PIDFD (since Linux 5.4) wait for the child referred to by the PID file descriptor specified in id. (See the Linux pidfd_open(2) man page for further information on PID file descriptors.)
NetBSD and FreeBSD specific idtype and id arguments
If idtype is P_UID wait for processes whose effective user ID is equal to id.
If idtype is P_GID wait for processes whose effective group ID is equal to id.
If idtype is P_SID wait for processes whose session ID is equal to id. If the child process started its own session, its session ID will be the same as its process ID. Otherwise the session ID of a child process will match the caller's session ID.
FreeBSD specific idtype and id arguments
If idtype is P_JAILID wait for processes within a jail whose jail identifier is equal to id.
info

The info parameter is set to an array containing information about the signal.

info array may contain the following keys:

  • signo: Signal number
  • errno: System error number
  • code: Signal code
  • status: Exit value or signal
  • pid: Sending process ID
  • uid: Real user ID of sending process
  • utime: User time consumed
  • stime: System time consumed

flags

The value of flags is the value of zero or more of the following constants OR'ed together:

possible values for flags
WCONTINUED Status shall be returned for any continued child process whose status either has not been reported since it continued from a job control stop or has been reported only by calls to pcntl_waitid with the WNOWAIT flag set.
WEXITED Wait for processes that have exited.
WNOHANG Do not hang if no status is available; return immediately.
WNOWAIT Keep the process whose status is returned in info in a waitable state. This shall not affect the state of the process; the process may be waited for again after this call completes.
WSTOPPED Status shall be returned for any child that has stopped upon receipt of a signal, and whose status either has not been reported since it stopped or has been reported only by calls to pcntl_waitid with the WNOWAIT flag set.

resource_usage

The resource_usage parameter is set to an array containing resource usage statistics from the child process. This is supported either if the wait6 system call is available (e.g. on FreeBSD), or on Linux through the raw waitid system call.

Return Values

pcntl_waitid returns true if WNOHANG was specified and status is not available for any process specified by idtype and id.

pcntl_waitid returns true due to the change of state of one of its children.

Otherwise, false is returned and pcntl_get_last_error can be used to get the errno error number.

Note:

Once an errno error number has been obtained, pcntl_strerror can be used to get the text message associated with it.

Errors/Exceptions

Error number (errno) values
ECHILD The calling process has no existing unwaited-for child processes.
EINTR pcntl_waitid was interrupted by a signal.
EINVAL An invalid value was specified for flags, or idtype and id specify an invalid set of processes.

Changelog

Version Description
8.5.0 resource_usage was added.

See Also

  • pcntl_waitpid
  • pcntl_wait
  • pcntl_fork
  • pcntl_signal
  • pcntl_wifexited
  • pcntl_wifstopped
  • pcntl_wifsignaled
  • pcntl_wexitstatus
  • pcntl_wtermsig
  • pcntl_wstopsig