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| <h3 class="section">24.4 Defining Signal Handlers</h3> |
| |
| <p><a name="index-signal-handler-function-2930"></a> |
| This section describes how to write a signal handler function that can |
| be established with the <code>signal</code> or <code>sigaction</code> functions. |
| |
| <p>A signal handler is just a function that you compile together with the |
| rest of the program. Instead of directly invoking the function, you use |
| <code>signal</code> or <code>sigaction</code> to tell the operating system to call |
| it when a signal arrives. This is known as <dfn>establishing</dfn> the |
| handler. See <a href="Signal-Actions.html#Signal-Actions">Signal Actions</a>. |
| |
| <p>There are two basic strategies you can use in signal handler functions: |
| |
| <ul> |
| <li>You can have the handler function note that the signal arrived by |
| tweaking some global data structures, and then return normally. |
| |
| <li>You can have the handler function terminate the program or transfer |
| control to a point where it can recover from the situation that caused |
| the signal. |
| </ul> |
| |
| <p>You need to take special care in writing handler functions because they |
| can be called asynchronously. That is, a handler might be called at any |
| point in the program, unpredictably. If two signals arrive during a |
| very short interval, one handler can run within another. This section |
| describes what your handler should do, and what you should avoid. |
| |
| <ul class="menu"> |
| <li><a accesskey="1" href="Handler-Returns.html#Handler-Returns">Handler Returns</a>: Handlers that return normally, and what |
| this means. |
| <li><a accesskey="2" href="Termination-in-Handler.html#Termination-in-Handler">Termination in Handler</a>: How handler functions terminate a program. |
| <li><a accesskey="3" href="Longjmp-in-Handler.html#Longjmp-in-Handler">Longjmp in Handler</a>: Nonlocal transfer of control out of a |
| signal handler. |
| <li><a accesskey="4" href="Signals-in-Handler.html#Signals-in-Handler">Signals in Handler</a>: What happens when signals arrive while |
| the handler is already occupied. |
| <li><a accesskey="5" href="Merged-Signals.html#Merged-Signals">Merged Signals</a>: When a second signal arrives before the |
| first is handled. |
| <li><a accesskey="6" href="Nonreentrancy.html#Nonreentrancy">Nonreentrancy</a>: Do not call any functions unless you know they |
| are reentrant with respect to signals. |
| <li><a accesskey="7" href="Atomic-Data-Access.html#Atomic-Data-Access">Atomic Data Access</a>: A single handler can run in the middle of |
| reading or writing a single object. |
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