0                  Indicates success. There are no stopped or
                       exited child processes, the WNOHANG option is
                       specified.
    x                  The process_id of the child process. The
                       status of a child process is available.
    -1                 Indicates an error; errno is set to one of the
                       following values:

                       o  ECHILD - There are no child processes to
                          wait for.

                       o  EINTR - Terminated by receipt of a signal
                          intercepted by the calling process.

                       o  EFAULT - The status_location or resource_
                          usage argument points to a location outside
                          of the address space of the process.

                       o  EINVAL- The value of the options argument
                          is not valid.