wait3, wait4 - wait for process to change state, BSD style

#include <sys/wait.h>
pid_t wait3(int *_Nullable wstatus, int options,
 struct rusage *_Nullable rusage);
pid_t wait4(pid_t pid, int *_Nullable wstatus, int options,
 struct rusage *_Nullable rusage);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

    Since glibc 2.26:
        _DEFAULT_SOURCE
            || (_XOPEN_SOURCE >= 500 &&
                ! (_POSIX_C_SOURCE >= 200112L
                   || _XOPEN_SOURCE >= 600))
    From glibc 2.19 to glibc 2.25:
        _DEFAULT_SOURCE || _XOPEN_SOURCE >= 500
    glibc 2.19 and earlier:
        _BSD_SOURCE || _XOPEN_SOURCE >= 500

    Since glibc 2.19:
        _DEFAULT_SOURCE
    glibc 2.19 and earlier:
        _BSD_SOURCE

These functions are nonstandard; in new programs, the use of waitpid(2) or waitid(2) is preferable.

The wait3() and wait4() system calls are similar to waitpid(2), but additionally return resource usage information about the child in the structure pointed to by rusage.

Other than the use of the rusage argument, the following wait3() call:

wait3(wstatus, options, rusage);

is equivalent to:

waitpid(-1, wstatus, options);

Similarly, the following wait4() call:

wait4(pid, wstatus, options, rusage);

is equivalent to:

waitpid(pid, wstatus, options);

In other words, wait3() waits of any child, while wait4() can be used to select a specific child, or children, on which to wait. See wait(2) for further details.

If rusage is not NULL, the struct rusage to which it points will be filled with accounting information about the child. See getrusage(2) for details.

As for waitpid(2).

fork(2), getrusage(2), sigaction(2), signal(2), wait(2), signal(7)