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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; see section Special Characters) to send it an interactive stop 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 ANSI C committee. Older systems may not support it, so using kill may be more portable. See section Signaling Another Process.

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