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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.

DESCRIPTION top

Thewaitid() function shall obtain status information (seeSection2.13,Status Information) pertaining to termination, stop, and/or continue events in one of the caller's child processes. Thewaitid() 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 theidtype andid arguments. * The state change in the status information matches one of the state change flags set in theoptions argument. If matching status information is available prior to the call towaitid(), 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 inSection 2.13,Status Information, thewaitid() function consumes the status information it obtains unless the WNOWAIT flag is set in theoptions argument. The behavior when multiple threads are blocked inwait(),waitid(), orwaitpid() is described inSection 2.13,StatusInformation. Thewaitid() function shall record the obtained status information in the structure pointed to byinfop. The fields of the structure pointed to byinfop shall be filled in as described under ``Pointer to a Function'' inSection 2.4.3,Signal Actions. Theidtype andid arguments are used to specify which childrenwaitid() waits for. Ifidtype is P_PID,waitid() shall wait for the child with a process ID equal to (pid_t)id. Ifidtype is P_PGID,waitid() shall wait for any child with a process group ID equal to (pid_t)id. Ifidtype is P_ALL,waitid() shall wait for any children andid is ignored. Theoptions argument is used to specify which state changeswaitid() 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 towaitid() 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 ininfop 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 towaitid() with the WNOWAIT flag set. Applications shall specify at least one of the flags WEXITED, WSTOPPED, or WCONTINUED to be OR'ed in with theoptions argument. The application shall ensure that theinfop argument points to asiginfo_tstructure. Ifwaitid() returns because a child process was found that satisfied the conditions indicated by the argumentsidtype andoptions, then the structure pointed to byinfop shall be filled in by the system with the status of the process; thesi_signo member shall be set equal to SIGCHLD. Ifwaitid() returns because WNOHANG was specified and status is not available for any process specified byidtype andid, then thesi_signo andsi_pid members of the structure pointed to byinfop shall be set to zero and the values of other members of the structure are unspecified.

If WNOHANG was specified and status is not available for any process specified byidtype andid, 0 shall be returned. Ifwaitid() returns due to the change of state of one of its children, 0 shall be returned. Otherwise, -1 shall be returned anderrno set to indicate the error.

ERRORS top

Thewaitid() function shall fail if:ECHILDThe calling process has no existing unwaited-for child processes.EINTRThewaitid() function was interrupted by a signal.EINVALAn invalid value was specified foroptions, oridtype andid specify an invalid set of processes.The following sections are informative.

APPLICATION USAGE top

Calls towaitid() withidtype 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 ofsystem()). For this reason it is recommended that portable applications not usewaitid() with idtype of P_ALL. See also APPLICATION USAGE forwait(). As specified inConsequences 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 inwait(),waitid(), orwaitpid(). 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).

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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group 2017WAITID(3P)