21.1. Designing Signal Handlers

In general, it is preferable to write simple signal handlers. One important reason for this is to reduce the risk of creating race conditions. Two common designs for signal handlers are the following:

• The signal handler sets a global flag and exits. The main program periodically checks this flag and, if it is set, takes appropriate action. (If the main program cannot perform such periodic checks because it needs to monitor one or more file descriptors to see if I/O is possible, then the signal handler can also write a single byte to a dedicated pipe whose read end is included among the file descriptors monitored by the main program. We show an example of this technique in Section 63.5.2.)

• The signal handler performs some type of cleanup and then either terminates the process or uses a nonlocal goto (Section 21.2.1) to unwind the stack and return control to a predetermined location in the main program.