wait4(2) DG/UX 5.4.2 wait4(2)
NAME
wait4 - wait for the specified child process to stop or terminate
SYNOPSIS
#include <sys/wait.h>
#include <sys/time.h>
#include <sys/resource.h>
int wait4 (childpid, waitstatus, options, rusage)
int childpid;
union wait * waitstatus;
int options;
struct rusage * rusage;
where:
childpid The process id for the child process that we are
waiting on
waitstatus NULL or address of a status word
options Modifications to the action of wait3
rusage NULL or address of a resource usage structure
DESCRIPTION
Wait4 suspends the calling process until the specified child process
stops or terminates, then reports the identity, status, and resource
usage of the child process to the calling process.
⊕ A process "stops" when it is being traced (see ptrace) and
either hits a break point or receives a signal that is set to
be caught.
⊕ A process "terminates" when it calls exit either directly or
due to the receipt of a signal that causes the process to
terminate.
⊕ A process that has terminated, but whose status has not been
reported on by wait may consume system resources. The wait
operation "cleans-up" the terminated process and recovers
remaining system resources.
The status of the child process is optionally obtained by the
waitstatus parameter. If waitstatus is NULL, status information is
not returned. Otherwise, 16 bits of status information are stored in
the low-order 16 bits of the location pointed to by waitstatus.
waitstatus can be used to determine the reason for the child
process' termination.
The following macros are provided in sys/wait.h for use in
interpreting waitstatus. When using these macros with wait4, the
program must define _BSD_WAIT_FLAVOR either in the executable or at
compile time.
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wait4(2) DG/UX 5.4.2 wait4(2)
WIFSTOPPED(*waitstatus)
Evaluates to a non-zero value if status was returned for a
child process that is currently stopped.
WIFSIGNALED(*waitstatus)
Evaluates to a non-zero value if status was returned for a
child process that terminated due to the receipt of a signal
that was not
WIFEXITED(*waitstatus)
Evaluates to a non-zero value if status was returned for a
child process that terminated normally.
A summary of the resources used by a child process that has
terminated is obtained by the rusage parameter. If rusage is NULL, a
summary is not returned. Otherwise, summary
A summary of the resources used by a child process that has
terminated is obtained by the rusage parameter. If rusage is NULL, a
summary is not returned. Otherwise, summary information is stored in
the location pointed to by rusage.
Wait4(2) is identical to wait3(2) except that it waits only on one
specified child. Siblings of the specified children are ignored. If
the caller specifies childpid as zero, wait4 behaves identically to
wait3.
The action taken by wait4 may be modified by setting bits in the
options parameter as follows.
⊕ The WNOHANG bit specifies that the calling process should not
be suspended by wait4.
⊕ A process that is not being traced may be stopped by the
SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signals. The WUNTRACED
bit specifies that the status of all stopped child processes
should be reported, not just those being traced.
If a parent process terminates without waiting for its child
processes to terminate, a special system process inherits the child
processes.
If an error occurs, wait4 will not clean-up any process and the
values of status and rusage are undefined.
If, while waiting for a child to terminate or stop, the process
receives a signal that causes it to invoke a handler, wait4 will be
restarted if the handler was established using sigvec without the
SV_INTERRUPT flag or sigaction with the SA_RESTART flag. See
sigvec(2) and sigaction(2).
ACCESS CONTROL
None.
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wait4(2) DG/UX 5.4.2 wait4(2)
RETURN VALUE
child-process-id Completed successfully.
0 The WNOHANG bit in options was set and the calling
process would otherwise have been suspended by
wait3.
-1 An error occurred. errno is set to indicate the
error.
DIAGNOSTICS
Errno may be set to one of the following error codes:
ECHILD The calling process has no child processes. This condition
implies that the calling process was not suspended by
wait3.
EFAULT The status or rusage arguments point to an illegal address.
This condition implies that the calling process was not
suspended by wait3.
SEE ALSO
exec(2), exit(2), fork(2), ptrace(2), sigpause(2), sigvec(2),
sigaction(2), wait(2), wait3(2), exit(3C).
STANDARDS
When using m88kbcs as the Software Development Environment target,
the wait4 function will be an incomplete emulation of Berkeley
semantics. Since we are using BCS system calls, resource usage
information is not available. If rusage is non-NULL, wait4() will
fail with errno set to EINVAL.
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