wait(3) C LIBRARY FUNCTIONS wait(3)
NAME
wait, wait3, WIFSTOPPED, WIFSIGNALED, WIFEXITED - wait for
process to terminate or stop
SYNOPSIS
cc [ flag... ] file ... -lucb #include <sys/wait.h>
int wait(statusp)
union wait *statusp;
#include <sys/time.h>
#include <sys/resource.h>
int wait3(statusp, options, rusage)
union wait *statusp;
int options;
struct rusage *rusage;
WIFSTOPPED(status)
union wait status;
WIFSIGNALED(status)
union wait status;
WIFEXITED(status)
union wait status;
DESCRIPTION
wait delays its caller until a signal is received or one of
its child processes terminates or stops due to tracing. If
any child has died or stopped due to tracing and this has
not been reported using wait, return is immediate, returning
the process ID and exit status of one of those children. If
that child had died, it is discarded. If there are no chil-
dren, return is immediate with the value -1 returned. If
there are only running or stopped but reported children, the
calling process is blocked. If status is not a NULL
pointer, then on return from a successful wait call the
status of the child process whose process ID is the return
value of wait is stored in the wait union pointed to by
status. The w_status member of that union is an int; it
indicates the cause of termination and other information
about the terminated process in the following manner:
⊕ If the low-order 8 bits of w_status are equal to
0177, the child process has stopped; the 8 bits
higher up from the low-order 8 bits of w_status con-
tain the number of the signal that caused the pro-
cess to stop. See ptrace(2) and sigvec(3).
⊕ If the low-order 8 bits of w_status are non-zero and
are not equal to 0177, the child process terminated
due to a signal; the low-order 7 bits of w_status
contain the number of the signal that terminated the
process. In addition, if the low-order seventh bit
of w_status (that is, bit 0200) is set, a ``core
image'' of the process was produced; see sigvec(3).
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wait(3) C LIBRARY FUNCTIONS wait(3)
⊕ Otherwise, the child process terminated due to an
exit call; the 8 bits higher up from the low-order 8
bits of w_status contain the low-order 8 bits of the
argument that the child process passed to exit; see
exit(2).
Other members of the wait union can be used to extract this
information more conveniently:
⊕ If the w_stopval member has the value WSTOPPED, the
child process has stopped; the value of the
w_stopsig member is the signal that stopped the pro-
cess.
⊕ If the w_termsig member is non-zero, the child pro-
cess terminated due to a signal; the value of the
w_termsig member is the number of the signal that
terminated the process. If the w_coredump member is
non-zero, a core dump was produced.
⊕ Otherwise, the child process terminated due to an
exit call; the value of the w_retcode member is the
low-order 8 bits of the argument that the child pro-
cess passed to exit.
The other members of the wait union merely provide an alter-
nate way of analyzing the status. The value stored in the
w_status field is compatible with the values stored by other
versions of the UNIX system, and an argument of type int *
may be provided instead of an argument of type union wait *
for compatibility with those versions. wait3 is an alter-
nate interface that allows both non-blocking status collec-
tion and the collection of the status of children stopped by
any means. The status parameter is defined as above. The
options parameter is used to indicate the call should not
block if there are no processes that have status to report
(WNOHANG), and/or that children of the current process that
are stopped due to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP
signal are eligible to have their status reported as well
(WUNTRACED). A terminated child is discarded after it
reports status, and a stopped process will not report its
status more than once. If rusage is not a NULL pointer, a
summary of the resources used by the terminated process and
all its children is returned. Only the user time used and
the system time used are currently available. They are
returned in rusage.ru_utime and rusage.ru_stime, respec-
tively. When the WNOHANG option is specified and no
processes have status to report, wait3 returns 0. The
WNOHANG and WUNTRACED options may be combined by ORing the
two values. WIFSTOPPED, WIFSIGNALED, WIFEXITED, are macros
that take an argument status, of type `union wait', as
returned by wait, or wait3. WIFSTOPPED evaluates to true
(1) when the process for which the wait call was made is
stopped, or to false (0) otherwise. WIFSIGNALED evaluates
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wait(3) C LIBRARY FUNCTIONS wait(3)
to true when the process was terminated with a signal.
WIFEXITED evaluates to true whe the process exited by using
an exit(2) call.
RETURN VALUE
If wait returns due to a stopped or terminated child pro-
cess, 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. wait3 returns 0 if WNOHANG is
specified and there are no stopped or exited children, and
returns the process ID of the child process if it returns
due to a stopped or terminated child process. Otherwise,
wait3 returns a value of -1 and sets errno to indicate the
error.
ERRORS
wait, or wait3 will fail and return immediately if one or
more of the following are true:
ECHILD The calling process has no existing
unwaited-for child processes.
EFAULT The status or rusage arguments point to an
illegal address. wait, and wait3 will ter-
minate prematurely, return -1, and set errno
to EINTR upon the arrival of a signal whose
SV_INTERRUPT bit in its flags field is set
[see sigvec(3) and siginterrupt(3)]. sig-
nal(3), in the System V compatibility
library, sets this bit for any signal it
catches.
SEE ALSO
sigvec(3), getrusage(3), siginterrupt(3), signal(3) exit(2),
ptrace(2), signal(2) wait(2), waitpid(2) in the Programmer's
Reference Manual.
NOTES
If a parent process terminates without waiting on its chil-
dren, the initialization process (process ID = 1) inherits
the children. wait, and wait3 are automatically restarted
when a process receives a signal while awaiting termination
of a child process, unless the SV_INTERRUPT bit is set in
the flags for that signal.
WARNINGS
Calls to wait with an argument of 0 should be cast to type
`union wait *', as in:
wait((union wait *)0) Otherwise lint will complain.
Last change: BSD Compatibility Package 3