in reply to Split process->check ->and run Parallel

Have p1 fork and exec p2. Have p2 write the txt report and then send a signal (with kill and getppid) to p1. After the fork, p1 can just sleep until it gets that signal. It would probably be a good idea to have p1 check that p2 is still alive (with kill or waitpid) once in a while. Once p1 gets its signal, it can do what it wants with the txt report while p2 works on the Excel report. When p1 is ready to wait again, just waitpid for p2 and check its exit status to make sure there was no error.

  • Comment on Re: Split process->check ->and run Parallel

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Re^2: Split process->check ->and run Parallel
by matrixmadhan (Beadle) on Dec 24, 2008 at 10:32 UTC
    It would probably be a good idea to have p1 check that p2 is still alive (with kill or waitpid) once in a while

    But, why is this needed, if a child process is terminated/killed a SIGCHLD will be delivered to the parent by default, so I don't think an explicit check for the existence of the child process is needed
[reply]
      matrixmadhan:

      It's me again!

      The kill function doesn't have to terminate another process. There are other signals that it can send. You can send several different signals to another process with it, such as:

      $ kill -l
 1) SIGHUP       2) SIGINT       3) SIGQUIT      4) SIGILL
 5) SIGTRAP      6) SIGABRT      7) SIGEMT       8) SIGFPE
 9) SIGKILL     10) SIGBUS      11) SIGSEGV     12) SIGSYS
13) SIGPIPE     14) SIGALRM     15) SIGTERM     16) SIGURG
17) SIGSTOP     18) SIGTSTP     19) SIGCONT     20) SIGCHLD
21) SIGTTIN     22) SIGTTOU     23) SIGIO       24) SIGXCPU
25) SIGXFSZ     26) SIGVTALRM   27) SIGPROF     28) SIGWINCH
29) SIGLOST     30) SIGUSR1     31) SIGUSR2     32) SIGRTMAX

      [download]

      If both processes agree on a signal for communication, then you can put a signal handling function in your processes to receive the messages. For example, you could use SIGUSR1 to let P2 tell P1 that the text report is done. Then you could send SIGUSR2 to indicate that the spreadsheet is done.

      ...roboticus
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[d/l]
[select]
        I agree that communication between parent and child to be established via the signals provided and that would prove to be more robust and synchronous instead of communication being asynchronous when its not needed.

        :)
[reply]

      You're right. The parent can just trap SIGCHLD and whatever "I'm done" signal the child is sending and sleep.

[reply]

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