pid_t
wait(
int *status
)
pid_t
waitpid(
pid_t wpid
, int *status
, int options
)
pid_t
wait3(
int *status
, int options
, struct rusage *rusage
)
pid_t
wait4(
pid_t wpid
, int *status
, int options
, struct rusage *rusage
)
)
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()
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(
).
The
wpid
parameter specifies the set of child processes for which to wait.
If
wpid
is -1, the call waits for any child process.
If
wpid
is 0,
the call waits for any child process in the process group of the caller.
If
wpid
is greater than zero, the call waits for the process with process id
wpid
.
If
wpid
is less than -1, the call waits for any process whose process group id
equals the absolute value of
wpid
.
The
status
parameter is defined below.
The
options
parameter contains the bitwise OR of any of the following options:
WNOHANG
WUNTRACED
SIGTTIN
, SIGTTOU
, SIGTSTP
,
or
SIGSTOP
signal also have their status reported.
WALTSIG
SIGCHLD
when they exit.
If
WALTSIG
is not specified, the call will wait only for processes that
are configured to post
SIGCHLD
.
__WCLONE
WALTSIG
.
It is provided for compatibility with the Linux
clone(2)
API.
WALLSIG
__WALL
WALLSIG
.
It is provided for compatibility with the Linux
clone(2)
API .
If
rusage
is non-zero, a summary of the resources used by the terminated
process and all its
children is returned (this information is currently not available
for stopped processes).
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:
status
)
status
)
status
)
WUNTRACED
option
or if the child process is being traced (see
ptrace(2)).
Depending on the values of those macros, the following macros produce the remaining status information about the child process:
status
)
status
)
is true, evaluates to the low-order 8 bits
of the argument passed to
_exit(2)
or
exit(3)
by the child.
status
)
status
)
is true, evaluates to the number of the signal
that caused the termination of the process.
status
)
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.
status
)
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
intro(2),
System call restart.
)
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
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.
)
will fail and return immediately if:
ECHILD
]
EFAULT
]
status
or
rusage
arguments point to an illegal address.
(May not be detected before exit of a child process.)
EINTR
]
SA_RESTART
flag set.
In addition,
wait3(),
wait4(
),
and
waitpid(
)
will fail and return immediately if:
EINVAL
]
options
.
)
and
waitpid(
)
functions conform to
ISO/IEC 9945-1:1990 (``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.
)
function call appeared in
Version 6 AT&T UNIX
.