waitid(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

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

NAME         top

       waitid — wait for a child process to change state

SYNOPSIS         top

       #include <sys/wait.h>

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

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       Section 2.4.3, Signal Actions, Section 2.13, Status Information,
       exec(1p), exit(3p), wait(3p)

       The Base Definitions volume of POSIX.1‐2017, signal.h(0p),
       sys_wait.h(0p)

COPYRIGHT         top

       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(3P)

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