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<a name="In_002dProcess-Agent"></a>
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<a name="In_002dProcess-Agent-1"></a>
<h2 class="chapter">30 In-Process Agent</h2>
<a name="index-debugging-agent"></a>
<p>The traditional debugging model is conceptually low-speed, but works fine,
because most bugs can be reproduced in debugging-mode execution.  However,
as multi-core or many-core processors are becoming mainstream, and
multi-threaded programs become more and more popular, there should be more
and more bugs that only manifest themselves at normal-mode execution, for
example, thread races, because debugger&rsquo;s interference with the program&rsquo;s
timing may conceal the bugs.  On the other hand, in some applications,
it is not feasible for the debugger to interrupt the program&rsquo;s execution
long enough for the developer to learn anything helpful about its behavior.
If the program&rsquo;s correctness depends on its real-time behavior, delays
introduced by a debugger might cause the program to fail, even when the
code itself is correct.  It is useful to be able to observe the program&rsquo;s
behavior without interrupting it.
</p>
<p>Therefore, traditional debugging model is too intrusive to reproduce
some bugs.  In order to reduce the interference with the program, we can
reduce the number of operations performed by debugger.  The
<em>In-Process Agent</em>, a shared library, is running within the same
process with inferior, and is able to perform some debugging operations
itself.  As a result, debugger is only involved when necessary, and
performance of debugging can be improved accordingly.  Note that
interference with program can be reduced but can&rsquo;t be removed completely,
because the in-process agent will still stop or slow down the program.
</p>
<p>The in-process agent can interpret and execute Agent Expressions
(see <a href="Agent-Expressions.html#Agent-Expressions">Agent Expressions</a>) during performing debugging operations.  The
agent expressions can be used for different purposes, such as collecting
data in tracepoints, and condition evaluation in breakpoints.
</p>
<a name="Control-Agent"></a><p>You can control whether the in-process agent is used as an aid for
debugging with the following commands:
</p>
<dl compact="compact">
<dd><a name="index-set-agent-on"></a>
</dd>
<dt><code>set agent on</code></dt>
<dd><p>Causes the in-process agent to perform some operations on behalf of the
debugger.  Just which operations requested by the user will be done
by the in-process agent depends on the its capabilities.  For example,
if you request to evaluate breakpoint conditions in the in-process agent,
and the in-process agent has such capability as well, then breakpoint
conditions will be evaluated in the in-process agent.
</p>
<a name="index-set-agent-off"></a>
</dd>
<dt><code>set agent off</code></dt>
<dd><p>Disables execution of debugging operations by the in-process agent.  All
of the operations will be performed by <small>GDB</small>.
</p>
<a name="index-show-agent"></a>
</dd>
<dt><code>show agent</code></dt>
<dd><p>Display the current setting of execution of debugging operations by
the in-process agent.
</p></dd>
</dl>

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