1WAITID(3P) POSIX Programmer's Manual WAITID(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 waitid — wait for a child process to change state
13
15 #include <sys/wait.h>
16 int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
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20 The waitid() function shall obtain status information (see Section
21 2.13, Status Information) pertaining to termination, stop, and/or con‐
22 tinue events in one of the caller's child processes.
23 The waitid() function shall cause the calling thread to become blocked
25 until an error occurs or status information becomes available to the
26 calling thread that satisfies all of the following properties (``match‐
27 ing status information''):
28 * The status information is from one of the child processes in the
30 set of child processes specified by the idtype and id arguments.
31 * The state change in the status information matches one of the state
33 change flags set in the options argument.
34 If matching status information is available prior to the call to
36 waitid(), return shall be immediate. If matching status information is
37 available for two or more child processes, the order in which their
38 status is reported is unspecified.
39 As described in Section 2.13, Status Information, the waitid() function
41 consumes the status information it obtains unless the WNOWAIT flag is
42 set in the options argument.
43 The behavior when multiple threads are blocked in wait(), waitid(), or
45 waitpid() is described in Section 2.13, Status Information.
46 The waitid() function shall record the obtained status information in
48 the structure pointed to by infop. The fields of the structure pointed
49 to by infop shall be filled in as described under ``Pointer to a Func‐
50 tion'' in Section 2.4.3, Signal Actions.
51 The idtype and id arguments are used to specify which children waitid()
53 waits for.
54 If idtype is P_PID, waitid() shall wait for the child with a process ID
56 equal to (pid_t)id.
57 If idtype is P_PGID, waitid() shall wait for any child with a process
59 group ID equal to (pid_t)id.
60 If idtype is P_ALL, waitid() shall wait for any children and id is
62 ignored.
63 The options argument is used to specify which state changes waitid()
65 shall wait for. It is formed by OR'ing together the following flags:
66 WCONTINUED Status shall be returned for any continued child process
68 whose status either has not been reported since it contin‐
69 ued from a job control stop or has been reported only by
70 calls to waitid() with the WNOWAIT flag set.
71 WEXITED Wait for processes that have exited.
73 WNOHANG Do not hang if no status is available; return immediately.
75 WNOWAIT Keep the process whose status is returned in infop in a
77 waitable state. This shall not affect the state of the
78 process; the process may be waited for again after this
79 call completes.
80 WSTOPPED Status shall be returned for any child that has stopped
82 upon receipt of a signal, and whose status either has not
83 been reported since it stopped or has been reported only by
84 calls to waitid() with the WNOWAIT flag set.
85 Applications shall specify at least one of the flags WEXITED, WSTOPPED,
87 or WCONTINUED to be OR'ed in with the options argument.
88 The application shall ensure that the infop argument points to a sig‐
90 info_t structure. If waitid() returns because a child process was found
91 that satisfied the conditions indicated by the arguments idtype and
92 options, then the structure pointed to by infop shall be filled in by
93 the system with the status of the process; the si_signo member shall be
94 set equal to SIGCHLD. If waitid() returns because WNOHANG was speci‐
95 fied and status is not available for any process specified by idtype
96 and id, then the si_signo and si_pid members of the structure pointed
97 to by infop shall be set to zero and the values of other members of the
98 structure are unspecified.
99
101 If WNOHANG was specified and status is not available for any process
102 specified by idtype and id, 0 shall be returned. If waitid() returns
103 due to the change of state of one of its children, 0 shall be returned.
104 Otherwise, -1 shall be returned and errno set to indicate the error.
105
107 The waitid() function shall fail if:
108 ECHILD The calling process has no existing unwaited-for child pro‐
110 cesses.
111 EINTR The waitid() function was interrupted by a signal.
113 EINVAL An invalid value was specified for options, or idtype and id
115 specify an invalid set of processes.
116 The following sections are informative.
118
120 None.
121
123 Calls to waitid() with idtype equal to P_ALL will collect information
124 about any child process. This may result in interactions with other
125 interfaces that may be waiting for their own children (such as by use
126 of system()). For this reason it is recommended that portable applica‐
127 tions not use waitid() with idtype of P_ALL. See also APPLICATION USAGE
128 for wait().
129 As specified in Consequences of Process Termination, if the calling
131 process has SA_NOCLDWAIT set or has SIGCHLD set to SIG_IGN, then the
132 termination of a child process will not cause status information to
133 become available to a thread blocked in wait(), waitid(), or waitpid().
134 Thus, a thread blocked in one of the wait functions will remain blocked
135 unless some other condition causes the thread to resume execution (such
136 as an [ECHILD] failure due to no remaining children in the set of
137 waited-for children).
138
140 None.
141
143 None.
144
146 Section 2.4.3, Signal Actions, Section 2.13, Status Information, exec,
147 exit(), wait()
148 The Base Definitions volume of POSIX.1‐2017, <signal.h>, <sys_wait.h>
150
152 Portions of this text are reprinted and reproduced in electronic form
153 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
154 table Operating System Interface (POSIX), The Open Group Base Specifi‐
155 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
156 Electrical and Electronics Engineers, Inc and The Open Group. In the
157 event of any discrepancy between this version and the original IEEE and
158 The Open Group Standard, the original IEEE and The Open Group Standard
159 is the referee document. The original Standard can be obtained online
160 at http://www.opengroup.org/unix/online.html .
161 Any typographical or formatting errors that appear in this page are
163 most likely to have been introduced during the conversion of the source
164 files to man page format. To report such errors, see https://www.ker‐
165 nel.org/doc/man-pages/reporting_bugs.html .
166IEEE/The Open Group 2017 WAITID(3P)