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<h2 class="title"><a id="program"></a>Chapter 15. Programmer Notes </h2>
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<b>Table of Contents</b>
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<dt>
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<span class="sect1">
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<span class="sect1">
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<span class="sect2">
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<div>
<h2 class="title" style="clear: both"><a id="program_appsignals"></a>Signal handling</h2>
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</div>
<p>
When applications using Berkeley DB receive signals, it is
important that they exit gracefully, discarding any Berkeley
DB locks that they may hold. This is normally done by setting
a flag when a signal arrives and then checking for that flag
periodically within the application. Because Berkeley DB is
not re-entrant, the signal handler should not attempt to
release locks and/or close the database handles itself.
Re-entering Berkeley DB is not guaranteed to work correctly,
and the results are undefined.
</p>
<p>
If an application exits holding a lock, the situation is no
different than if the application crashed, and all
applications participating in the database environment must be
shut down, and then recovery must be performed. If this is not
done, databases may be left in an inconsistent state, or locks
the application held may cause unresolvable deadlocks inside
the environment, causing applications to hang.
</p>
<p>
Berkeley DB restarts all system calls interrupted by
signals, that is, any underlying system calls that return
failure with errno set to EINTR will be restarted rather than
failing.
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<a accesskey="h" href="index.html">Home</a>
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