wait4(3C)
NAME
wait3, wait4 - wait for process to terminate or stop
SYNOPSIS
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
pid_t wait3(int *statusp, int options, struct rusage
*rusage);
pid_t wait4(pid_t pid, int *statusp, int options, struct
rusage *rusage);
DESCRIPTION
The wait3() 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 already been reported, return is
immediate, returning the process ID and status of one of
those children. If that child process has died, it is dis-
carded. If there are no children, -1 is returned immedi-
ately. If there are only running or stopped but reported
children, the calling process is blocked.
If statusp is not a null pointer, then on return from a suc-
cessful wait3() call, the status of the child process is
stored in the integer pointed to by statusp. *statusp indi-
cates the cause of termination and other information about
the terminated process in the following manner:
o If the low-order 8 bits of *statusp are equal to 0177,
the child process has stopped; the 8 bits higher up
from the low-order 8 bits of *statusp contain the
number of the signal that caused the process to stop.
See signal(3HEAD).
o If the low-order 8 bits of *statusp are non-zero and
are not equal to 0177, the child process terminated
due to a signal; the low-order 7 bits of *statusp con-
tain the number of the signal that terminated the pro-
cess. In addition, if the low-order seventh bit of
*statusp (that is, bit 0200) is set, a ``core image''
of the process was produced; see signal(3HEAD).
o Otherwise, the child process terminated due to an
exit() call; the 8 bits higher up from the low-order 8
bits of *statusp contain the low-order 8 bits of the
argument that the child process passed to exit(); see
exit(2).
The options argument is constructed from the bitwise
inclusive OR of zero or more of the following flags, defined
in <sys/wait.h>:
WNOHANG
Execution of the calling process is not suspended if
status is not immediately available for any child pro-
cess.
WUNTRACED
The status of any child processes that are stopped,
and whose status has not yet been reported since they
stopped, are also reported to the requesting process.
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 the ru_utime
and ru_stime, members of the rusage structure, respectively.
When the WNOHANG option is specified and no processes have
status to report, wait3() returns 0. The WNOHANG and WUN-
TRACED options may be combined by the bitwise OR operation
of the two values.
The wait4() function is an extended 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.
The status can be evaluated using the macros defined by
wstat(3XFN).
RETURN VALUES
If wait3() or wait4() returns due to a stopped or terminated
child process, the process ID of the child is returned to
the calling process. Otherwise, -1 is returned and errno is
set to indicate the error.
If wait3() or wait4() return due to the delivery of a signal
to the calling process, -1 is returned and errno is set to
EINTR. If WNOHANG was 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, 0 is returned. Otherwise, -1 is returned
and errno is set to indicate the error.
The wait3() and wait4() functions return 0 if WNOHANG is
specified and there are no stopped or exited children, and
return the process ID of the child process if they return
due to a stopped or terminated child process. Otherwise,
they return -1 and set errno to indicate the error.
ERRORS
The wait3() and wait4() functions will fail and return
immediately if:
ECHILD
The calling process has no existing unwaited-for child
processes.
EFAULT
The statusp or rusage arguments point to an illegal
address.
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.
The wait4() function may fail if:
ECHILD
The process specified by pid does not exist or is not
a child of the calling process.
The wait3()and wait4() functions will terminate prematurely,
return -1, and set errno to EINTR upon the arrival of a sig-
nal whose SA_RESTART bit in its flags field is not set (see
sigaction(2)).
SEE ALSO
kill(1), exit(2), wait(2), waitid(2), waitpid(2),
getrusage(3C), signal(3C), proc(4), signal(3HEAD),
wstat(3XFN)
NOTES
If a parent process terminates without waiting on its chil-
dren, the initialization process (process ID = 1) inherits
the children.
The wait3() and wait4() functions are automatically res-
tarted when a process receives a signal while awaiting ter-
mination of a child process, unless the SA_RESTART bit is
not set in the flags for that signal.
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