wait3(2) System Calls Manual wait3(2)
NAME
wait3(), wait4() - wait for child process to change state
SYNOPSIS
DESCRIPTION
The and functions allow the calling process to obtain various status information for a caller's child process based on the options speci-
fied. If status information is available for two or more child processes, the order of which process to report status on is not defined.
The function is similar to except that waits for a specific child as indicated by the pid parameter.
Note that the following call
is equivalent to the call:
Note that the following call
is equivalent to the call:
In both of the previous prototypes, on successful completion, if the resource_usage argument to or is not a null pointer, the structure
that the resource_usage argument points to is filled in for the child process identified by the return value.
The pid argument specifies a child process for which status is requested. The following rules define which status information is returned:
o If pid is equal to (pid_t) -1, status is requested for any child process.
o If pid is greater than 0, it specifies the process ID of a single child process for which status is requested.
o If pid is 0, status is requested for any child process whose process group ID is equal to that of the calling process.
o If pid is less than (pid_t) -1, status is requested for any child process whose process group ID is equal to the absolute value
of pid.
The stat_loc argument is the address where status about the specified child process is placed.
The options argument is constructed from the bitwise-inclusive OR of zero or more of the following flags defined in the header file:
The status of any continued child process specified by
pid that has not been reported since it continued is reported to the requesting process.
The and functions will not suspend execution of the calling process if status is not immediately available for one of
the child processes specified by pid.
This causes the wait not to be registered.
This means that the registered process that is being waited on, can be waited on again with identical results,
provided that the status of the child does not change in the meantime.
The status of any child processes specified by
pid that are stopped and whose status has not yet been reported since they stopped, will also be reported to the
requesting process.
The resource_usage argument points to the resource utilization structure.
APPLICATION USAGE
Threads Considerations
In a multi-threaded application, only the calling thread is suspended by and
The and functions will not return until all threads in the process have reached the desired state. For example, and will not return until
all threads have terminated. If the or options are specified, and will not return until all threads have stopped or continued respec-
tively.
RETURN VALUE
If or returns because the status of a child process is available, the return value is the process ID of that child process. If or returns
due to the receipt of a signal, the return value receives a and is set to
If or was called with the options argument where status is not available for any process specified by the pid argument, will be returned.
Otherwise, (pid_t) will be returned and will be set to indicate the error.
ERRORS
If or fails, is set to one of the following values:
The calling process has no existing unwaited-for child processes;
or the states specified by the options argument are invalid for the set of processes specified by the pid argument.
Problems were encountered in the retrieval of status information for the
specified child process.
The or function has been interrupted by a signal. The value in the location pointed to by the stat_loc argument is unde-
fined.
The options argument to or is invalid.
WARNINGS
The behavior of and is affected if the signal is set to See the WARNINGS section of signal(5). Signal handlers that cause system calls to
be restarted can affect the condition described above (see bsdproc(3C) and sigaction(2)).
AUTHOR
The and functions were developed by HP, AT&T, and the University of California, Berkeley.
SEE ALSO
exec(2), exit(2), fork(2), pause(2), wait(2), waitpid(2).
wait3(2)