technical/api-sigchain.html

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 385 <body>
 386 <div id="header">
 387 <h1>sigchain API</h1>
 388 </div>
 389 <div id="preamble">
 390 <div class="sectionbody">
 391 <div class="paragraph"><p>Code often wants to set a signal handler to clean up temporary files or
 392 other work-in-progress when we die unexpectedly. For multiple pieces of
 393 code to do this without conflicting, each piece of code must remember
 394 the old value of the handler and restore it either when:</p></div>
 395 <div class="olist arabic"><ol class="arabic">
 396 <li>
 397 <p>
 398 The work-in-progress is finished, and the handler is no longer
 399      necessary. The handler should revert to the original behavior
 400      (either another handler, SIG_DFL, or SIG_IGN).
 401 </p>
 402 </li>
 403 <li>
 404 <p>
 405 The signal is received. We should then do our cleanup, then chain
 406      to the next handler (or die if it is SIG_DFL).
 407 </p>
 408 </li>
 409 </ol></div>
 410 <div class="paragraph"><p>Sigchain is a tiny library for keeping a stack of handlers. Your handler
 411 and installation code should look something like:</p></div>
 412 <div class="listingblock">
 413 <div class="content">
 414 <pre><tt>  void clean_foo_on_signal(int sig)
 415   {
 416           clean_foo();
 417           sigchain_pop(sig);
 418           raise(sig);
 419   }
 420
 421   void other_func()
 422   {
 423           sigchain_push_common(clean_foo_on_signal);
 424           mess_up_foo();
 425           clean_foo();
 426   }</tt></pre>
 427 </div></div>
 428 <div class="paragraph"><p>Handlers are given the typedef of sigchain_fun. This is the same type
 429 that is given to signal() or sigaction(). It is perfectly reasonable to
 430 push SIG_DFL or SIG_IGN onto the stack.</p></div>
 431 <div class="paragraph"><p>You can sigchain_push and sigchain_pop individual signals. For
 432 convenience, sigchain_push_common will push the handler onto the stack
 433 for many common signals.</p></div>
 434 </div>
 435 </div>
 436 <div id="footer">
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 438 Last updated 2011-01-04 22:05:44 UTC
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