wait3()

Wait for any child process to change its state

Synopsis:

#include <sys/wait.h>
#include <sys/resource.h>

pid_t wait3( int * stat_loc,
             int options,
             struct rusage * resource_usage );

Arguments:

stat_loc

NULL, or a pointer a location where the function can store the terminating status of the child process. For information about macros that extract information from this status, see “Status macros” in the documentation for wait().

options

A combination of zero or more of the following flags:

• WCONTINUED — return the status for any child that was stopped and has been continued.
• WNOHANG — return immediately if there are no children to wait for.
• WNOWAIT — keep the process in a waitable state. This doesn't affect the state of the process; the process may be waited for again after this call completion.
• WSTOPPED — wait for and return the process status of any child that has stopped because it received a signal.
• WUNTRACED — report the status of a stopped child process. In QNX Neutrino, this is the same as WSTOPPED.

resource_usage

NULL, or a pointer to a rusage structure where the function can store information about resource usage. For information about this structure, see getrusage().

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The wait3() function allows the calling thread to obtain status information for specified child processes.

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If the parent process sets the action for SIGCHLD to SIG_IGN, its children won't enter the zombie state, and it won't be able to use the wait*() functions to wait on their deaths.

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The following call:

wait3( stat_loc, options, resource_usage );

is equivalent to:

waitpid( (pid_t)-1, stat_loc, options );

except that on successful completion, if the resource_usage argument to wait3() isn't a null pointer, the rusage structure that the third argument points to is filled in for the child process identified by the return value.

It's also equivalent to:

wait4( (pid_t)-1, stat_loc, options, resource_usage );

The waitpid() function is POSIX: wait3() and wait4() are BSD extensions.

Returns:

If the status of a child process is available, a value equal to the process ID of the child process for which status is reported.

If a signal is delivered to the calling process, -1 and errno is set to EINTR.

Zero if wait3() is invoked with WNOHANG set in options and at least one child process is specified by pid for which status isn't available, and status isn't available for any process specified by pid.

Otherwise, (pid_t)-1 and errno is set.

Errors:

ECHILD

The calling process has no existing unwaited-for child processes, or the set of processes specified by the argument pid can never be in the states specified by the argument options.

Classification:

Unix

See also:

exit(), fork(), pause(), wait4(), waitid(), waitpid()

“Detecting process termination” in the “Processes” chapter of the QNX Neutrino Programmer's Guide