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| <h4 class="subsection">24.7.4 Blocking to Test for Delivery of a Signal</h4> |
| |
| <p>Now for a simple example. Suppose you establish a handler for |
| <code>SIGALRM</code> signals that sets a flag whenever a signal arrives, and |
| your main program checks this flag from time to time and then resets it. |
| You can prevent additional <code>SIGALRM</code> signals from arriving in the |
| meantime by wrapping the critical part of the code with calls to |
| <code>sigprocmask</code>, like this: |
| |
| <pre class="smallexample"> /* <span class="roman">This variable is set by the SIGALRM signal handler.</span> */ |
| volatile sig_atomic_t flag = 0; |
| |
| int |
| main (void) |
| { |
| sigset_t block_alarm; |
| |
| ... |
| |
| /* <span class="roman">Initialize the signal mask.</span> */ |
| sigemptyset (&block_alarm); |
| sigaddset (&block_alarm, SIGALRM); |
| |
| while (1) |
| { |
| /* <span class="roman">Check if a signal has arrived; if so, reset the flag.</span> */ |
| sigprocmask (SIG_BLOCK, &block_alarm, NULL); |
| if (flag) |
| { |
| <var>actions-if-not-arrived</var> |
| flag = 0; |
| } |
| sigprocmask (SIG_UNBLOCK, &block_alarm, NULL); |
| |
| ... |
| } |
| } |
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