24.7 Blocking Signals

Blocking a signal means telling the operating system to hold it and deliver it later. Generally, a program does not block signals indefinitely—it might as well ignore them by setting their actions to SIG_IGN. But it is useful to block signals briefly, to prevent them from interrupting sensitive operations. For instance:

• You can use the sigprocmask function to block signals while you modify global variables that are also modified by the handlers for these signals.
• You can set sa_mask in your sigaction call to block certain signals while a particular signal handler runs. This way, the signal handler can run without being interrupted itself by signals.

• Why Block: The purpose of blocking signals.
• Signal Sets: How to specify which signals to block.
• Process Signal Mask: Blocking delivery of signals to your process during normal execution.
• Testing for Delivery: Blocking to Test for Delivery of a Signal.
• Blocking for Handler: Blocking additional signals while a handler is being run.
• Checking for Pending Signals: Checking for Pending Signals
• Remembering a Signal: How you can get almost the same effect as blocking a signal, by handling it and setting a flag to be tested later.