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. |