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In fact, POSIX recommends sigaction(2) and deprecates signal(2). Unfortunately, sigaction(2) is not C99-compliant, and is not supported on some platforms, including Windows.
Exceptions
SIG34-EX1: On a machine with persistent signal handlers, it is safe for a handler to modify the behavior for its own signal. This would include having the signal be ignored, reset to default behavior, or handled by a different handler. A handler assigning itself to its own signal is also safe, as it is a no-op. The handler is impervious to a race condition since multiple invocations of its signal will merely cause it to 'interrupt itself', until it manages to reassign its signal.
The following code example resets a signal to the system's default behavior.
| Code Block | ||
|---|---|---|
| ||
void handler(int signum) {
#ifndef WINDOWS
signal(signum, SIG_DFL);
#endif
/* handling code */
}
/* ... */
signal(signum, handler);
|
Not all systems have persistent signal handlers. For more info, see SIG01-A. Understand implementation-specific details regarding signal handler persistence
Risk Assessment
Two signals in quick succession can trigger the race condition on non-persistent platforms, thereby causing the signal's default behavior despite a handler's attempt to override it.
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