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| <h2 class="chapter">30 In-Process Agent</h2> |
| |
| <p><a name="index-debugging-agent-3161"></a>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's interference with the program's |
| timing may conceal the bugs. On the other hand, in some applications, |
| it is not feasible for the debugger to interrupt the program's execution |
| long enough for the developer to learn anything helpful about its behavior. |
| If the program'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's |
| behavior without interrupting it. |
| |
| <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 |
| <dfn>In-Process Agent</dfn>, 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't be removed completely, |
| because the in-process agent will still stop or slow down the program. |
| |
| <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>You can control whether the in-process agent is used as an aid for |
| debugging with the following commands: |
| |
| |
| <a name="index-set-agent-on-3162"></a> |
| <dl><dt><code>set agent on</code><dd>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-3163"></a><br><dt><code>set agent off</code><dd>Disables execution of debugging operations by the in-process agent. All |
| of the operations will be performed by <span class="sc">gdb</span>. |
| |
| <p><a name="index-show-agent-3164"></a><br><dt><code>show agent</code><dd>Display the current setting of execution of debugging operations by |
| the in-process agent. |
| </dl> |
| |
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| <li><a accesskey="1" href="In_002dProcess-Agent-Protocol.html#In_002dProcess-Agent-Protocol">In-Process Agent Protocol</a> |
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