WAITID(2) System Calls WAITID(2)
NAME
waitid - wait for child process to change state
SYNOPSIS
#include <wait.h>
int waitid(
idtype_t idtype,
id_t id,
siginfo_t *infop,
int options);
DESCRIPTION
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:
o If
idtype is
P_PID,
waitid() waits for the child with a
process
ID equal to
(pid_t)id.
o If
idtype is
P_PGID,
waitid() waits for any child with a
process group
ID equal to
(pid_t)id.
o 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:
WCONTINUED Return the status for any child that was stopped and
has been continued.
WEXITED Wait for process(es) to exit.
WNOHANG Return immediately.
WNOWAIT Keep the process in a waitable state.
WSTOPPED Wait for and return the process status of any child
that has stopped upon receipt of a signal.
WTRAPPED 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
SIGCHLD.
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.
RETURN VALUES
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.
ERRORS
The
waitid() function will fail if:
ECHILD The set of processes specified by
idtype and
id does not
contain any unwaited processes.
EFAULT The
infop argument points to an illegal address.
EINTR The
waitid() function was interrupted due to the receipt of
a signal by the calling process.
EINVAL An invalid value was specified for
options, or
idtype and
id specify an invalid set of processes.
USAGE
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).
ATTRIBUTES
See
attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+
SEE ALSO
Intro(2),
exec(2),
exit(2),
fork(2),
pause(2),
sigaction(2),
ptrace(3C),
signal(3C),
wait(3C),
waitpid(3C),
siginfo.h(3HEAD),
attributes(7),
standards(7) June 8, 2018 WAITID(2)
