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| <h4 class="subsection">24.6.1 Signaling Yourself</h4> |
| |
| <p>A process can send itself a signal with the <code>raise</code> function. This |
| function is declared in <samp><span class="file">signal.h</span></samp>. |
| <a name="index-signal_002eh-2948"></a> |
| <!-- signal.h --> |
| <!-- ISO --> |
| |
| <div class="defun"> |
| — Function: int <b>raise</b> (<var>int signum</var>)<var><a name="index-raise-2949"></a></var><br> |
| <blockquote><p>The <code>raise</code> function sends the signal <var>signum</var> 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 <var>signum</var> |
| is invalid. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- SVID --> |
| <div class="defun"> |
| — Function: int <b>gsignal</b> (<var>int signum</var>)<var><a name="index-gsignal-2950"></a></var><br> |
| <blockquote><p>The <code>gsignal</code> function does the same thing as <code>raise</code>; it is |
| provided only for compatibility with SVID. |
| </p></blockquote></div> |
| |
| <p>One convenient use for <code>raise</code> 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 <kbd>C-z</kbd>; see <a href="Special-Characters.html#Special-Characters">Special Characters</a>) to send it an interactive stop signal |
| (<code>SIGTSTP</code>), and you want to clean up some internal data buffers |
| before stopping. You might set this up like this: |
| |
| <!-- RMS suggested getting rid of the handler for SIGCONT in this function. --> |
| <!-- But that would require that the handler for SIGTSTP unblock the --> |
| <!-- signal before doing the call to raise. We haven't covered that --> |
| <!-- topic yet, and I don't want to distract from the main point of --> |
| <!-- the example with a digression to explain what is going on. As --> |
| <!-- the example is written, the signal that is raise'd will be delivered --> |
| <!-- as soon as the SIGTSTP handler returns, which is fine. --> |
| <pre class="smallexample"> #include <signal.h> |
| |
| /* <span class="roman">When a stop signal arrives, set the action back to the default |
| and then resend the signal after doing cleanup actions.</span> */ |
| |
| void |
| tstp_handler (int sig) |
| { |
| signal (SIGTSTP, SIG_DFL); |
| /* <span class="roman">Do cleanup actions here.</span> */ |
| ... |
| raise (SIGTSTP); |
| } |
| |
| /* <span class="roman">When the process is continued again, restore the signal handler.</span> */ |
| |
| void |
| cont_handler (int sig) |
| { |
| signal (SIGCONT, cont_handler); |
| signal (SIGTSTP, tstp_handler); |
| } |
| |
| /* <span class="roman">Enable both handlers during program initialization.</span> */ |
| |
| int |
| main (void) |
| { |
| signal (SIGCONT, cont_handler); |
| signal (SIGTSTP, tstp_handler); |
| ... |
| } |
| </pre> |
| <p><strong>Portability note:</strong> <code>raise</code> was invented by the ISO C<!-- /@w --> |
| committee. Older systems may not support it, so using <code>kill</code> may |
| be more portable. See <a href="Signaling-Another-Process.html#Signaling-Another-Process">Signaling Another Process</a>. |
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