waitid - wait for child process to change state
int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
The waitid() function suspends the calling process until one of its child
processes changes state. It records the current state of a child in the
structure pointed to by infop. It returns immediately if a child
process changed state prior to the call.
The idtype and id arguments specify which children
waitid() is to wait for, as follows:
- If idtype is P_PID, waitid() waits for the child with
a process ID equal to (pid_t)id.
- If idtype is P_PGID, waitid() waits for any child
with a process group ID equal to (pid_t)id.
- If idtype is P_ALL, waitid() waits for any child and
id is ignored.
The options argument is used to specify which state changes
waitid() is to wait for. It is formed by bitwise OR operation
of any of the following flags:
Return the status for any child that was stopped and has
Wait for process(es) to exit.
Keep the process in a waitable state.
Wait for and return the process status of any child that
has stopped upon receipt of a signal.
Wait for traced process(es) to become trapped or reach a
breakpoint (see ptrace(3C)
The infop argument must point to a siginfo_t
structure, as defined in siginfo.h(3HEAD). If waitid() returns
because a child process was found that satisfies the conditions indicated by
the arguments idtype and options, then the structure pointed
to by infop will be filled by the system with the status of the
process. The si_signo member will always be equal to
One instance of a SIGCHLD signal is queued for each child
process whose status has changed. If waitid() returns because the
status of a child process is available and WNOWAIT was not specified
in options, any pending SIGCHLD signal associated with the
process ID of that child process is discarded. Any other pending
SIGCHLD signals remain pending.
If waitid() returns due to a change of state of one of its children and
WNOHANG was not used, 0 is returned. Otherwise, −1
is returned and errno is set to indicate the error. If WNOHANG
was used, 0 can be returned (indicating no error); however, no children
may have changed state if infop->si_pid is 0.
The waitid() function will fail if:
The set of processes specified by idtype and
id does not contain any unwaited processes.
The infop argument points to an illegal
The waitid() function was interrupted due to the
receipt of a signal by the calling process.
An invalid value was specified for options, or
idtype and id specify an invalid set of processes.
With options equal to WEXITED | WTRAPPED, waitid()
is equivalent to waitpid(3C). With idtype equal to P_ALL
and options equal to WEXITED | WTRAPPED, waitid()
is equivalent to wait(3C).
See attributes(7) for descriptions of the following attributes:
Intro(2), exec(2), exit(2), fork(2),
pause(2), sigaction(2), ptrace(3C), signal(3C),
wait(3C), waitpid(3C), siginfo.h(3HEAD),