gno/usr.man/man2/wait.2

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.\"     @(#)wait.2	8.2 (Berkeley) 4/19/94
.\"
.TH WAIT 2 "19 January 1997" GNO "System Calls"
.SH NAME
.BR wait ,
.BR waitpid ,
.BR wait4 ,
.BR wait3
\- wait for process termination
.SH SYNOPSIS
#include <sys/types.h>
.br
#include <sys/wait.h>
.sp 1
pid_t
\fBwait\fR (union wait *\fIstatus\fR);
.sp 1
#include <sys/time.h>
.br
#include <sys/resource.h>
.sp 1
pid_t
\fBwaitpid\fR (pid_t \fIwpid\fR, union wait *\fIstatus\fR, int \fIoptions\fR);
.sp 1
pid_t
\fBwait3\fR (union wait *\fIstatus\fR, int \fIoptions\fR, struct rusage *\fIrusage\fR);
.sp 1
pid_t
\fBwait4\fR (pid_t \fIwpid\fR, union wait *\fIstatus\fR, int \fIoptions\fR, struct rusage *\fIrusage\fR);
.SH DESCRIPTION
The
.BR wait 
function suspends execution of its calling process until
.I status
information is available for a terminated child process,
or a signal is received.
On return from a successful 
.BR wait 
call, 
the
.I status
area contains termination information about the process that exited
as defined below.
.LP
The
.BR 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.
.LP
The
.I wpid
parameter specifies the set of child processes for which to wait.
If
.I wpid
is -1, the call waits for any child process.
If
.I wpid
is 0,
the call waits for any child process in the process group of the caller.
If
.I wpid
is greater than zero, the call waits for the process with process id
.IR wpid .
If
.I wpid
is less than -1, the call waits for any process whose process group id
equals the absolute value of
.IR wpid .
.LP
The
.I status
parameter is defined below.  The
.I options
parameter contains the bitwise OR of any of the following options.
The
.BR WNOHANG
option
is used to indicate that the call should not block if
there are no processes that wish to report status.
If the
.BR WUNTRACED
option is set,
children of the current process that are stopped
due to a
.BR SIGTTIN , 
.BR SIGTTOU , 
.BR SIGTSTP ,
or
.BR SIGSTOP
signal also have
their status reported.
.LP
If
.I 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).
.LP
When the
.BR WNOHANG
option is specified and no processes
wish to report status, 
.BR wait4 
returns a process id of 0.
.LP
The
.BR waitpid 
call is identical to
.BR wait4 
with an
.I rusage
value of zero.
The older
.BR wait3 
call is the same as
.BR wait4 
with a
.I wpid
value of -1.
.LP
The following macros may be used to test the manner of exit of the process.
One of the first three macros will evaluate to a non-zero (true) value:
.RS
.IP \fBWIFEXITED\fR(\fIstatus\fR)
True if the process terminated normally by a call to
.BR _exit (2),
.BR exit (3),
.BR rexit (3),
or a GS/OS quit call.
.IP \fBWIFSIGNALED\fR(\fIstatus\fR)
True if the process terminated due to receipt of a signal.
.IP \fBWIFSTOPPED\fR(\fIstatus\fR)
True if the process has not terminated, but has stopped and can be restarted.
This macro can be true only if the wait call specified the
.BR WUNTRACED
option
or if the child process is being traced (see
.BR ptrace (2)).
.RE
.LP
Depending on the values of those macros, the following macros
produce the remaining status information about the child process:
.RS
.IP \fBWEXITSTATUS\fR(\fIstatus\fR)
If
\fBWIFEXITED\fR(\fIstatus\fR)
is true, evaluates to the low-order 8 bits
of the argument passed to
.BR _exit (2),
.BR exit (3),
.BR rexit (3),
or a GS/OS Quit call
by the child.
.IP \fBWTERMSIG\fR(\fIstatus\fR)
If
\fBWIFSIGNALED\fR(\fIstatus\fR)
is true, evaluates to the number of the signal
that caused the termination of the process.
.IP \fBWCOREDUMP\fR(\fIstatus\fR)
If
\fBWIFSIGNALED\fR(\fIstatus\fR)
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.
.I "This feature is not available under GNO."
.IP \fBWSTOPSIG\fR(\fIstatus\fR)
If
\fBWIFSTOPPED\fR(\fIstatus\fR)
is true, evaluates to the number of the signal
that caused the process to stop.
.RE
.SH NOTES
See
.BR signal (2)
for a list of termination signals.
A status of 0 indicates normal termination.
.LP
Some Unix uses of these functions expect
.IR status
to be a pointer to an
.BR int
rather than to a
.BR "union wait" .
It is safe to use a cast under such circumstances.
.LP
If a parent process terminates without
waiting for all of its child processes to terminate,
the remaining child processes 
are inherited by the Kernel Null Process (pid zero).
.LP
If a signal is caught while any of the
.BR 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
.BR intro (2),
System call restart.
.SH BUGS
Currently, only
.BR wait
is implemented in the GNO kernel.  There is a minimal version of 
.BR waitpid
in the libraries, but that version of 
.BR waitpid
ignores its
.IR options
parameter
(making it impossible to make a non-blocking wait).
It may also give unexpected results when there is more than one
child task being waited upon.
.LP
.BR wait4
and 
.BR wait3
are not implemented.
.SH RETURN VALUES
If
.BR 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
.IR errno
is set to indicate the error.
.LP
If
.BR wait4 ,
.BR wait3 
or
.BR 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
.IR errno
set to ECHILD.
Otherwise, if
.BR 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
.IR errno
is set to indicate the error.
.SH ERRORS
.BR Wait 
will fail and return immediately if:
.RS
.IP \fBECHILD\fR
The calling process has no existing unwaited-for
child processes.
.IP \fBEFAULT\fR
The
.I status
or
.I rusage
arguments point to an illegal address.
(May not be detected before exit of a child process.)
.IP \fBEINTR\fR
The call was interrupted by a caught signal,
or the signal did not have the
.BR SA_RESTART
flag set.
.RE
.SH STANDARDS
The
.BR wait 
and
.BR waitpid 
functions are defined by POSIX;
.BR wait4 
and
.BR wait3 
are not specified by POSIX.
The
.BR WCOREDUMP 
macro
and the ability to restart a pending
.BR wait 
call are extensions to the POSIX interface.
.SH SEE ALSO
.BR _exit (2),
.BR execve (2),
.BR signal (2),
.BR exit (3)
.BR rexit (3)
.SH HISTORY
A
.BR wait3
function call appeared in Version 6 AT&T UNIX.