waitid

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



PROLOG
       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
       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(3P)