wait(3UCB) SunOS/BSD Compatibility Library Functions wait(3UCB)NAME
wait, wait3, wait4, waitpid, WIFSTOPPED, WIFSIGNALED, WIFEXITED - wait
for process to terminate or stop
SYNOPSIS
/usr/ucb/cc [ flag ... ] file ...
#include <sys/wait.h>
int wait(statusp)
int *statusp;
int waitpid(pid, statusp, options)
int pid;
int *statusp;
int options;
#include <sys/time.h>
#include <sys/resource.h>
int wait3(statusp, options, rusage)
int *statusp;
int options;
struct rusage *rusage;
int wait4(pid, statusp, options, rusage)
int pid;
int *statusp;
int options;
struct rusage *rusage;
WIFSTOPPED(status)
int status;
WIFSIGNALED(status)
int status;
WIFEXITED(status)
int status;
DESCRIPTION
The wait() function delays its caller until a signal is received or one
of its child processes terminates or stops due to tracing. If any child
process 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 process has
died, it is discarded. If there are no children, 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 sta‐
tus. 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:
o 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 contain the number of the sig‐
nal that caused the process to stop. Seeptrace(3C) and
sigvec(3UCB).
o 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(3UCB).
o 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).
waitpid() behaves identically to wait() if pid has a value of −1 and
options has a value of zero. Otherwise, the behavior of waitpid() is
modified by the values of pid and options as follows:
pid specifies a set of child processes for which status is requested.
waitpid() only returns the status of a child process from this set.
o If pid is equal to −1, status is requested for any child
process. In this respect, waitpid() is then equivalent to
wait().
o If pid is greater than zero, it specifies the process ID of
a single child process for which status is requested.
o If pid is equal to zero, status is requested for any child
process whose process group ID is equal to that of the call‐
ing process.
o If pid is less than −1, status is requested for any child
process whose process group ID is equal to the absolute
value of pid.
options is constructed from the bitwise inclusive OR of zero or more of
the following flags, defined in the header <sys/wait.h>:
WNOHANG waitpid() does not suspend execution of the calling
process if status is not immediately available for one of
the child processes specified by pid.
WUNTRACED The status of any child processes specified by pid that
are stopped, and whose status has not yet been reported
since they stopped, are also reported to the requesting
process.
wait3() is an alternate interface that allows both non-blocking status
collection 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 cur‐
rent process that are stopped due to a SIGTTIN, SIGTTOU, SIGTSTP, or
SIGSTOP signal are eligible to have their status reported as well (WUN‐
TRACED). 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, respectively.
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.
wait4() is another alternate interface. With a pid argument of 0, it
is equivalent to wait3(). If pid has a nonzero value, then wait4()
returns status only for the indicated process ID, but not for any other
child processes.
WIFSTOPPED, WIFSIGNALED, WIFEXITED, are macros that take an argument
status, of type int, as returned by wait(), or wait3(), or wait4().
WIFSTOPPED evaluates to true (1) when the process for which the wait()
call was made is stopped, or to false (0) otherwise. WIFSIGNALED evalu‐
ates to true when the process was terminated with a signal. WIFEXITED
evaluates to true when the process exited by using an exit(2) call.
RETURN VALUES
If wait()or waitpid() 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 indi‐
cate the error.
If wait() or waitpid() return due to the delivery of a signal to the
calling process, a value of −1 is returned and errno is set to EINTR.
If waitpid() function was invoked with WNOHANG set in options, it has
at least one child process specified by pid for which status is not
available, and status is not available for any process specified by
pid, a value of zero is returned. Otherwise, a value of −1 is returned,
and errno is set to indicate the error.
wait3() and wait4() return 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, they returns a value of −1 and sets errno to indicate the
error.
ERRORS
The wait(), wait3() and wait4() functions will fail and return immedi‐
ately if:
ECHILD The calling process has no existing unwaited-for child pro‐
cesses.
EFAULT The status or rusage arguments point to an illegal address.
waitpid() may set errno to:
ECHILD The process or process group specified by pid does not exist
or is not a child of the calling process.
EINTR The function was interrupted by a signal. The value of the
location pointed to by statusp is undefined.
EINVAL The value of options is not valid.
wait(), and wait3(), and wait4() will terminate 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(3UCB) and siginter‐
rupt(3UCB)). signal(3UCB), sets this bit for any signal it catches.
SEE ALSOcc(1B), exit(2), getrusage(3C), ptrace(3C), siginterrupt(3UCB), sig‐
nal(3C), signal(3UCB), sigvec(3UCB), wait(3C), waitpid(3C)NOTES
Use of these interfaces should be restricted to only applications writ‐
ten on BSD platforms. Use of these interfaces with any of the system
libraries or in multi-thread applications is unsupported.
If a parent process terminates without waiting on its children, the
initialization process (process ID = 1) inherits the children.
The wait(), wait3(), and wait4() functions 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 sig‐
nal.
Calls to wait() with an argument of 0 should be cast to type `int *',
as in:
wait((int *)0)
Previous SunOS releases used union wait*statusp and union wait status
in place of int *statusp and int status. The union contained a member
w_status that could be treated in the same way as status.
Other members of the wait union could be used to extract this informa‐
tion more conveniently:
o If the w_stopval member had the value WSTOPPED, the child
process had stopped; the value of the w_stopsig member was
the signal that stopped the process.
o If the w_termsig member was non-zero, the child process ter‐
minated due to a signal; the value of the w_termsig member
was the number of the signal that terminated the process.
If the w_coredump member was non-zero, a core dump was pro‐
duced.
o Otherwise, the child process terminated due to a call to
exit(). The value of the w_retcode member was the low-order
8 bits of the argument that the child process passed to
exit().
union wait is obsolete in light of the new specifications provided by
IEEE Std 1003.1-1988 and endorsed by SVID89 and XPG3. SunOS Release 4.1
supports unionwait for backward compatibility, but it will disappear in
a future release.
SunOS 5.10 30 Oct 2007 wait(3UCB)
