Other versions of Wait

• pid_t waitpid(pid_t pid, int *wstatus, int options);
  • needs sys/wait.h
  • takes a pid
    • Some of the options we do not know yet.
    • But if it is a positive integer, it waits for that pid.
    • If it is -1, it waits for any child process.
    • Other options are available for other situations.
  • Status is as with wait.
  • Options
    • These can be or-ed together
    • WNOHANG - return, do not block if no child has exited.
    • WUNTRACED - return when the child has stopped.
    • WCONTINUED - return if a child is continued.
  • See wpid.cpp
• int waitid(idtype_t idtype, id_t id, siginfo_t *infop, int options);
  • Better control over the processes selected.
  • There is a WNOWAIT option, which says to ignore the child specified.
    • But it can be grabbed later.
  • you get a structure back with far more information
  • Look at /usr/include/bits/types/siginfo_t.h, wow!
  • idtype
    • P_PID: Wait fo the given process id.
    • P_PIDFD: A file desrciptor wait. Ignore for now.
    • P_PGID: Any process in the process group of id. 0->All children
    • P_PALL: Ignore the id field. Wait for any child.
  • And these fields
    • si_pid : the pid child process that exited.
    • si_uid : the real user id of the child.
    • si_signo: SIGCHILD
    • si_code: One of
      CLD_EXITED
      • CLD_KILLED
      • CLD_DUMPED
      • CLD_STOPPED
      • CLD_TRAPPED
      • CLD_CONTINUED
      • si_status : the exit status, or the signal that caused the exit, based on si_code
    • See wid.cpp
  • There are two other versions

    •        pid_t wait3(int *wstatus, int options, struct rusage *rusage);
             pid_t wait4(pid_t pid, int *wstatus, int options,
                         struct rusage *rusage);

    • They return usage information (time )

      
                 struct rusage {
                     struct timeval ru_utime; /* user CPU time used */
                     struct timeval ru_stime; /* system CPU time used */
                     long   ru_maxrss;        /* maximum resident set size */
                     long   ru_ixrss;         /* integral shared memory size */
                     long   ru_idrss;         /* integral unshared data size */
                     long   ru_isrss;         /* integral unshared stack size */
                     long   ru_minflt;        /* page reclaims (soft page faults) */
                     long   ru_majflt;        /* page faults (hard page faults) */
                     long   ru_nswap;         /* swaps */
                     long   ru_inblock;       /* block input operations */
                     long   ru_oublock;       /* block output operations */
                     long   ru_msgsnd;        /* IPC messages sent */
                     long   ru_msgrcv;        /* IPC messages received */
                     long   ru_nsignals;      /* signals received */
                     long   ru_nvcsw;         /* voluntary context switches */
                     long   ru_nivcsw;        /* involuntary context switches */
                 };
             

    • I don't know this structure, but we can look at it later if you wish.
    • These are not standard, and should be avoided.