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(libc.info)Signaling Yourself

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Next: Signaling Another Process Up: Generating Signals

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Signaling Yourself
------------------

   A process can send itself a signal with the `raise' function.  This
function is declared in `signal.h'.

 - Function: int raise (int SIGNUM)
     The `raise' function sends the signal SIGNUM to the calling
     process.  It returns zero if successful and a nonzero value if it
     fails.  About the only reason for failure would be if the value of
     SIGNUM is invalid.

 - Function: int gsignal (int SIGNUM)
     The `gsignal' function does the same thing as `raise'; it is
     provided only for compatibility with SVID.

   One convenient use for `raise' is to reproduce the default behavior
of a signal that you have trapped.  For instance, suppose a user of your
program types the SUSP character (usually `C-z'; Note: Special
Characters) to send it an interactive stop signal (`SIGTSTP'), and
you want to clean up some internal data buffers before stopping.  You
might set this up like this:

     #include <signal.h>
     
     /* When a stop signal arrives, set the action back to the default
        and then resend the signal after doing cleanup actions. */
     
     void
     tstp_handler (int sig)
     {
       signal (SIGTSTP, SIG_DFL);
       /* Do cleanup actions here. */
       ...
       raise (SIGTSTP);
     }
     
     /* When the process is continued again, restore the signal handler. */
     
     void
     cont_handler (int sig)
     {
       signal (SIGCONT, cont_handler);
       signal (SIGTSTP, tstp_handler);
     }
     
     /* Enable both handlers during program initialization. */
     
     int
     main (void)
     {
       signal (SIGCONT, cont_handler);
       signal (SIGTSTP, tstp_handler);
       ...
     }

   *Portability note:* `raise' was invented by the ISO C committee.
Older systems may not support it, so using `kill' may be more portable.
Note: Signaling Another Process.