The waitid() function shall suspend the calling thread until one child of
the process containing the calling thread changes state. It records the
current state of a child in the structure pointed to by infop. If a
child process changed state prior to the call to waitid(),
waitid() shall return immediately. If more than one thread is suspended
in wait() or waitpid() waiting for termination of the same
process, exactly one thread shall return the process status at the time of the
target process termination.
The idtype and id arguments are used to specify which children
waitid() waits for.
If idtype is P_PID, waitid() shall wait for the child with a
process ID equal to ( pid_t)id.
If idtype is P_PGID, waitid() shall wait for any child with a
process group ID equal to ( pid_t)id.
If idtype is P_ALL, waitid() shall wait for any children and
id is ignored.
The options argument is used to specify which state changes
waitid() shall wait for. It is formed by OR'ing together one or more of
the following flags:
Wait for processes that have exited.
Status shall be returned for any child that has stopped
upon receipt of a signal.
Status shall be returned for any child that was stopped and
has been continued.
Return immediately if there are no children to wait
Keep the process whose status is returned in infop
in a waitable state. This shall not affect the state of the process; the
process may be waited for again after this call completes.
The application shall ensure that the infop argument points to a
siginfo_t structure. If waitid() returns because a child process
was found that satisfied the conditions indicated by the arguments
idtype and options, then the structure pointed to by
infop shall be filled in by the system with the status of the process.
The si_signo member shall always be equal to SIGCHLD.
If WNOHANG was specified and there are no children to wait for, 0 shall be
returned. If waitid() returns due to the change of state of one of its
children, 0 shall be returned. Otherwise, -1 shall be returned and
errno set to indicate the error.
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html