WAIT(2) | System Calls Manual | WAIT(2) |
wait
, waitid
,
waitpid
, wait6
,
wait4
, wait3
—
#include <sys/wait.h>
pid_t
wait
(int
*status);
pid_t
waitpid
(pid_t
wpid, int *status,
int options);
int
waitid
(idtype_t
idtype, id_t id,
siginfo_t *info,
int options);
#include
<sys/resource.h>
pid_t
wait3
(int
*status, int
options, struct rusage
*rusage);
pid_t
wait4
(pid_t
wpid, int *status,
int options,
struct rusage
*rusage);
pid_t
wait6
(idtype_t
idtype, id_t id,
int *status,
int options,
struct wrusage *wrusage,
siginfo_t *infop);
wait
() function suspends execution of its calling
process until status information is available for a
terminated child process, or a signal is received. On return from a successful
wait
() call, the status area
contains termination information about the process that exited as defined
below.
The wait4
() and
wait6
() call provides a more general interface for
programs that need to wait for certain child processes, that need resource
utilization statistics accumulated by child processes, or that require
options. The other wait functions are implemented using
wait4
(). or wait6
().
The wait6
() function is the most general
function in this family and its distinct features are:
All of the desired process statuses to be waited on must be
explicitly specified in options. The
wait
(), waitpid
(),
wait3
(), and wait4
()
functions all implicitly wait for exited and trapped processes, but the
waitid
() and wait6
()
functions require the corresponding WEXITED
and
WTRAPPED
flags to be explicitly specified. This
allows waiting for processes which have experienced other status changes
without having to also handle the exit status from terminated processes.
The wait6
() function accepts a
wrusage argument which points to a structure defined
as:
struct wrusage { struct rusage wru_self; struct rusage wru_children; };
This allows the calling process to collect resource usage
statistics from both its own child process as well as from its grand
children. When no resource usage statistics are needed this pointer can be
NULL
.
The last argument infop must be either
NULL
or a pointer to a
siginfo_t structure. If
non-NULL
, the structure is filled with the same data
as for a SIGCHLD
signal delivered when the process
changed state.
The set of child processes to be queried is specified by the arguments idtype and id. The separate idtype and id arguments support many other types of identifiers in addition to process IDs and process group IDs.
P_PID
,
waitid
() and wait6
() wait
for the child process with a process ID equal to
(pid_t)id
.P_PGID
,
waitid
() and wait6
() wait
for the child process with a process group ID equal to
(pid_t)id
.P_ALL
,
waitid
() and wait6
() wait
for any child process and the id
is ignored.P_PID
or
P_PGID
and the id
is zero,
waitid
() and wait6
() wait
for any child process in the same process group as the caller.Non-standard identifier types supported by this implementation of
waitid
() and wait6
()
are:
P_UID
(uid_t)
id.P_GID
(gid_t)
id.P_SID
For the waitpid
() and
wait4
() functions, the single
wpid argument specifies the set of child processes for
which to wait. The following symbolic constants are defined in
<sys/wait.h>
#define WAIT_ANY (-1) /* any process */ #define WAIT_MYPGRP 0 /* any process in my process group */
WAIT_ANY
, the
call waits for any child process.WAIT_MYPGRP
, the
call waits for any child process in the process group of the caller.The status argument is defined below.
The options argument contains the bitwise OR of any of the following options.
WALLSIG
WALTSIG
SIGCHLD
when they exit. If WALTSIG
is not specified, the
call will wait only for processes that are configured to post
SIGCHLD
.WCONTINUED
SIGCONT
signal.WEXITED
wait
(),
waitpid
(), wait3
(), and
wait4
().
waitid
() and wait6
()
functions, the flag has to be explicitly included in
options if status reports from terminated processes
are expected.WNOHANG
WNOWAIT
WNOZOMBIE
WSTOPPED
WUNTRACED
.WTRAPPED
wait
(), waitpid
(),
wait3
(), and wait4
().
waitid
() and wait6
()
functions, the flag has to be explicitly included in
options if status reports from trapped processes are
expected.WUNTRACED
SIGTTIN
, SIGTTOU
,
SIGTSTP
, or SIGSTOP
signal.__WALL
WALLSIG
. It is provided for
compatibility with the Linux
clone(2) API .__WCLONE
WALTSIG
. It is provided for
compatibility with the Linux
clone(2) API.For the waitid
() and
wait6
() functions, at least one of the options
WEXITED
, WUNTRACED
,
WSTOPPED
, WTRAPPED
, or
WCONTINUED
must be specified. Otherwise there will
be no events for the call to report. To avoid hanging indefinitely in such a
case these functions return -1 with errno
set to
EINVAL
.
If rusage is
non-NULL
, a summary of the resources used by the
terminated process and all its children is returned.
If wrusage is
non-NULL
, separate summaries are returned for the
resources used by the terminated process and the resources used by all its
children.
If infop is
non-NULL
, a siginfo_t
structure is returned with the si_signo field set to
SIGCHLD
and the si_pid field
set to the process ID of the process reporting status. For the exited
process, the si_status field of the
siginfo_t
structure contains the full 32 bit exit
status passed to _exit(2); the
status argument of other calls only returns 8 lowest
bits of the exit status.
When the WNOHANG
option is specified and
no processes wish to report status, waitid
() sets
the si_signo and si_pid fields
in infop to zero. Checking these fields is the only
way to know if a status change was reported.
When the WNOHANG
option is specified and
no processes wish to report status, wait4
() returns
a process id of 0.
The waitpid
() call is identical to
wait4
() with an rusage value
of zero. The older wait3
() call is the same as
wait4
() with a wpid value of
-1.
The following macros may be used to test the manner of exit of the process. Note that these macros expect the status value itself, not a pointer to the status value. One of the first three macros will evaluate to a non-zero (true) value:
WIFEXITED
(status)WIFSIGNALED
(status)WIFSTOPPED
(status)WUNTRACED
option or if the child process is being
traced (see ptrace(2)).WIFCONTINUED
(status)SIGCONT
signal. This macro can be
true only if the wait call specified the
WCONTINUED
option.Depending on the values of those macros, the following macros produce the remaining status information about the child process:
WEXITSTATUS
(status)WIFEXITED
(status) is
true, evaluates to the low-order 8 bits of the argument passed to
_exit(2) or
exit(3) by the child.WTERMSIG
(status)WIFSIGNALED
(status) is
true, evaluates to the number of the signal that caused the termination of
the process.WCOREDUMP
(status)WIFSIGNALED
(status) is
true, evaluates as true if the termination of the process was accompanied
by the creation of a core file containing an image of the process when the
signal was received.WSTOPSIG
(status)WIFSTOPPED
(status) is
true, evaluates to the number of the signal that caused the process to
stop.If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned the parent process 1 ID (the init process ID).
If a signal is caught while any of the
wait
() calls is pending, the call may be interrupted
or restarted when the signal-catching routine returns, depending on the
options in effect for the signal; see
siginterrupt(3).
wait
() returns due to a stopped or terminated child
process, the process ID of the child is returned to the calling process.
Otherwise, a value of -1 is returned and errno is set to
indicate the error.
If wait6
(),
wait4
(), wait3
() or
waitpid
() returns due to a stopped or terminated
child process, the process ID of the child is returned to the calling
process. If there are no children not previously awaited, -1 is returned
with errno set to [ECHILD
].
Otherwise, if WNOHANG
is specified and there are no
stopped or exited children, 0 is returned. If an error is detected or a
caught signal aborts the call, a value of -1 is returned and
errno is set to indicate the error.
If waitid
() returns because one or more
processes have a state change to report, 0 is returned. If an error is
detected, a value of -1 is returned and errno is set
to indicate the error. If WNOHANG
is specified and
there are no stopped, continued or exited children, 0 is returned. The
si_signo and si_pid fields of
infop must be checked against zero to determine if a
process reported status.
wait
() will fail and return immediately if:
ECHILD
]SIGCHLD
or setting the flag
SA_NOCLDWAIT
for that signal.EFAULT
]EINTR
]SA_RESTART
flag set.In addition, wait6
(),
wait3
(), wait4
(),
waitid
(), and waitpid
() will
fail and return immediately if:
EINVAL
]wait
() and waitpid
()
functions conform to IEEE Std 1003.1-1990
(“POSIX.1”); the waitid
()
function conforms to IEEE Std 1003.1-2004
(“POSIX.1”); the wait3
() function
conforms to X/Open Portability Guide Issue 4
(“XPG4”); wait4
() is an
extension. The WCOREDUMP
() macro and the ability to
restart a pending wait
() call are extensions to the
POSIX interface.
wait
() function call appeared in
Version 1 AT&T UNIX.
September 2, 2019 | NetBSD 9.0 |