WAITID(3)                  POSIX Programmer's Manual                 WAITID(3)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NAME
       waitid -- wait for a child process to change state

SYNOPSIS
       #include <sys/wait.h>

       int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);

DESCRIPTION
       The waitid() function shall obtain status information (see Section
       2.13, Status Information) pertaining to termination, stop, and/or
       continue events in one of the caller's child processes.

       The waitid() function shall cause the calling thread to become blocked
       until an error occurs or status information becomes available to the
       calling thread that satisfies all of the following properties
       (``matching status information''):

        *  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 options argument.

       If matching status information is available prior to the call to
       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.

       As described in Section 2.13, Status Information, the waitid() function
       consumes the status information it obtains unless the WNOWAIT flag is
       set in the options argument.

       The behavior when multiple threads are blocked in wait(), waitid(), or
       waitpid() is described in Section 2.13, Status Information.

       The waitid() function shall record the obtained status information in
       the structure pointed to by infop.  The fields of the structure pointed
       to by infop shall be filled in as described under ``Pointer to a
       Function'' in Section 2.4.3, Signal Actions.

       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 the following 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 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 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.

       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 waitid() with the WNOWAIT flag set.

       Applications shall specify at least one of the flags WEXITED, WSTOPPED,
       or WCONTINUED to be OR'ed in with the options argument.

       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
       be set equal to SIGCHLD.  If waitid() returns because WNOHANG was
       specified and status is not available for any process specified by
       idtype and id, then the si__signo and si__pid members of the structure
       pointed to by infop shall be set to zero and the values of other
       members of the structure are unspecified.

RETURN VALUE
       If WNOHANG was specified and status is not available for any process
       specified by idtype and id, 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.

ERRORS
       The waitid() function shall fail if:

       ECHILD The calling process has no existing unwaited-for child
              processes.

       EINTR  The waitid() function was interrupted by a signal.

       EINVAL An invalid value was specified for options, or idtype and id
              specify an invalid set of processes.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       Calls to waitid() with idtype equal to P_ALL will collect information
       about any child process. This may result in interactions with other
       interfaces that may be waiting for their own children (such as by use
       of system()).  For this reason it is recommended that portable
       applications not use waitid() with idtype of P_ALL. See also
       APPLICATION USAGE for wait().

       As specified in Consequences of Process Termination, if the calling
       process has SA_NOCLDWAIT set or has SIGCHLD set to SIG_IGN, then the
       termination of a child process will not cause status information to
       become available to a thread blocked in wait(), waitid(), or waitpid().
       Thus, a thread blocked in one of the wait functions will remain blocked
       unless some other condition causes the thread to resume execution (such
       as an [ECHILD] failure due to no remaining children in the set of
       waited-for children).

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.4.3, Signal Actions, Section 2.13, Status Information, exec,
       exit(), wait()

       The Base Definitions volume of POSIX.1-2017, <signal.h>, <sys_wait.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                            WAITID(3)
