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| <h4 class="subsection">24.3.5 Flags for <code>sigaction</code></h4> |
| |
| <p><a name="index-signal-flags-2922"></a><a name="index-flags-for-_0040code_007bsigaction_007d-2923"></a><a name="index-g_t_0040code_007bsigaction_007d-flags-2924"></a> |
| The <code>sa_flags</code> member of the <code>sigaction</code> structure is a |
| catch-all for special features. Most of the time, <code>SA_RESTART</code> is |
| a good value to use for this field. |
| |
| <p>The value of <code>sa_flags</code> is interpreted as a bit mask. Thus, you |
| should choose the flags you want to set, <span class="sc">or</span> those flags together, |
| and store the result in the <code>sa_flags</code> member of your |
| <code>sigaction</code> structure. |
| |
| <p>Each signal number has its own set of flags. Each call to |
| <code>sigaction</code> affects one particular signal number, and the flags |
| that you specify apply only to that particular signal. |
| |
| <p>In the GNU C library, establishing a handler with <code>signal</code> sets all |
| the flags to zero except for <code>SA_RESTART</code>, whose value depends on |
| the settings you have made with <code>siginterrupt</code>. See <a href="Interrupted-Primitives.html#Interrupted-Primitives">Interrupted Primitives</a>, to see what this is about. |
| |
| <p><a name="index-signal_002eh-2925"></a>These macros are defined in the header file <samp><span class="file">signal.h</span></samp>. |
| |
| <!-- signal.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Macro: int <b>SA_NOCLDSTOP</b><var><a name="index-SA_005fNOCLDSTOP-2926"></a></var><br> |
| <blockquote><p>This flag is meaningful only for the <code>SIGCHLD</code> signal. When the |
| flag is set, the system delivers the signal for a terminated child |
| process but not for one that is stopped. By default, <code>SIGCHLD</code> is |
| delivered for both terminated children and stopped children. |
| |
| <p>Setting this flag for a signal other than <code>SIGCHLD</code> has no effect. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: int <b>SA_ONSTACK</b><var><a name="index-SA_005fONSTACK-2927"></a></var><br> |
| <blockquote><p>If this flag is set for a particular signal number, the system uses the |
| signal stack when delivering that kind of signal. See <a href="Signal-Stack.html#Signal-Stack">Signal Stack</a>. |
| If a signal with this flag arrives and you have not set a signal stack, |
| the system terminates the program with <code>SIGILL</code>. |
| </p></blockquote></div> |
| |
| <!-- signal.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Macro: int <b>SA_RESTART</b><var><a name="index-SA_005fRESTART-2928"></a></var><br> |
| <blockquote><p>This flag controls what happens when a signal is delivered during |
| certain primitives (such as <code>open</code>, <code>read</code> or <code>write</code>), |
| and the signal handler returns normally. There are two alternatives: |
| the library function can resume, or it can return failure with error |
| code <code>EINTR</code>. |
| |
| <p>The choice is controlled by the <code>SA_RESTART</code> flag for the |
| particular kind of signal that was delivered. If the flag is set, |
| returning from a handler resumes the library function. If the flag is |
| clear, returning from a handler makes the function fail. |
| See <a href="Interrupted-Primitives.html#Interrupted-Primitives">Interrupted Primitives</a>. |
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