Description

   The wait3 function suspends the calling process until the request
   is completed, and redefines it so that only the calling thread is
   suspended.

   The options argument modifies the behavior of the function. You
   can combine the flags for the options argument by specifying
   their bitwise inclusive OR. The flags are:

   WNOWAIT        Specifies that the process whose status is
                  returned in status_location is kept in a waitable
                  state. You can wait for the process again with the
                  same results.
   WNOHANG        Prevents the suspension of the calling process.
                  If there are child processes that stopped or
                  terminated, one is chosen and the waitpid function
                  returns its process ID, as when you do not specify
                  the WNOHANG flag. If there are no terminated
                  processes (that is, if waitpid suspends the
                  calling process without the WNOHANG flag), 0
                  (zero) is returned. Because you can never wait
                  for process 0, there is no confusion arising from
                  this return.
   WUNTRACED      Specifies that the call return additional
                  information when the child processes of the
                  current process stop because the child process
                  received a SIGTTIN, SIGTTOU, SIGSTOP, or SIGTSTOP
                  signal.

   If the wait3 function returns because the status of a child
   process is available, the process ID of the child process is
   returned. Information is stored in the location pointed to by
   status_location, if this pointer is not null.

   The value stored in the location pointed to by status_location is
   0 (zero) only if the status is returned from a terminated child
   process that did one of the following:

   o  Returned 0 from the main function.

   o  Passed 0 as the status argument to the _exit or exit function.

   Regardless of the status_location value, you can define this
   information using the macros defined in the <wait.h> header file,
   which evaluate to integral expressions. In the following macro
   descriptions, the status_value argument is equal to the integer
   value pointed to by the status_location argument:

   WIFEXITED(status_  Evaluates to a nonzero value if status was
   value)             returned for a child process that terminated
                      normally.
   WEXITSTATUS(status_If the value of WIFEXITED(status_value) is
   value)             nonzero, this macro evaluates to the low-order
                      8 bits of the status argument that the child
                      process passed to the _exit or exit function,
                      or to the value the child process returned
                      from the main function.
   WIFSIGNALED(status_Evaluates to a nonzero value if status was
   value)             returned for a child process that terminated
                      due to the receipt of a signal that was not
                      intercepted.
   WTERMSIG(status_   If the value of WIFSIGNALED(status_value) is
   value)             nonzero, this macro evaluates to the number of
                      the signal that caused the termination of the
                      child process.
   WIFSTOPPED(status_ Evaluates to a nonzero value if status was
   value)             returned for a child process that is currently
                      stopped.
   WSTOPSIG(status_   If the value of WIFSTOPPED(status_value) is
   value)             nonzero, this macro evaluates to the number
                      of the signal that caused the child process to
                      stop.
   WIFCONTINUED(status_valuates to a nonzero value if status
   value)             was returned for a child process that has
                      continued.

   If the information stored at the location pointed to by status_
   location was stored there by a call to wait3 that specified
   the WUNTRACED flag, one of the following macros evaluates to a
   nonzero value:

   o  WIFEXITED(*status_value)

   o  WIFSIGNALED(*status_value)

   o  WIFSTOPPED(*status_value)

   o  WIFCONTINUED(*status_value)

   If the information stored in the location pointed to by status_
   location resulted from a call to wait3 without the WUNTRACED flag
   specified, one of the following macros evaluates to a nonzero
   value:

   o  WIFEXITED(*status_value)

   o  WIFSIGNALED(*status_value)

   The wait3 function provides compatibility with BSD systems.
   The resource_usage argument points to a location that contains
   resource usage information for the child processes as defined in
   the <resource.h> header file.

   If a parent process terminates without waiting for all of its
   child processes to terminate, the remaining child processes is
   assigned a parent process ID equal to the process ID of the init
   process.

   See also exit, -exit, and init.