подождите, пока дочерний процесс изменит состояние (wait for a child process to change state)
Пролог (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.
Имя (Name)
waitid — wait for a child process to change state
Синопсис (Synopsis)
#include <sys/wait.h>
int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
Описание (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.
Возвращаемое значение (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.
Ошибки (Error)
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.
Примеры (Examples)
None.
Использование в приложениях (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).
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
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)
