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| <a name="Asynchronous-and-non_002dstop-modes"></a> |
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| <a name="Asynchronous-command-execution-and-non_002dstop-mode"></a> |
| <h4 class="subsection">27.1.2 Asynchronous command execution and non-stop mode</h4> |
| |
| <p>On some targets, <small>GDB</small> is capable of processing MI commands |
| even while the target is running. This is called <em>asynchronous |
| command execution</em> (see <a href="Background-Execution.html#Background-Execution">Background Execution</a>). The frontend may |
| specify a preferrence for asynchronous execution using the |
| <code>-gdb-set mi-async 1</code> command, which should be emitted before |
| either running the executable or attaching to the target. After the |
| frontend has started the executable or attached to the target, it can |
| find if asynchronous execution is enabled using the |
| <code>-list-target-features</code> command. |
| </p> |
| <dl compact="compact"> |
| <dt><code>-gdb-set mi-async on</code></dt> |
| <dt><code>-gdb-set mi-async off</code></dt> |
| <dd><p>Set whether MI is in asynchronous mode. |
| </p> |
| <p>When <code>off</code>, which is the default, MI execution commands (e.g., |
| <code>-exec-continue</code>) are foreground commands, and <small>GDB</small> waits |
| for the program to stop before processing further commands. |
| </p> |
| <p>When <code>on</code>, MI execution commands are background execution |
| commands (e.g., <code>-exec-continue</code> becomes the equivalent of the |
| <code>c&</code> CLI command), and so <small>GDB</small> is capable of processing |
| MI commands even while the target is running. |
| </p> |
| </dd> |
| <dt><code>-gdb-show mi-async</code></dt> |
| <dd><p>Show whether MI asynchronous mode is enabled. |
| </p></dd> |
| </dl> |
| |
| <p>Note: In <small>GDB</small> version 7.7 and earlier, this option was called |
| <code>target-async</code> instead of <code>mi-async</code>, and it had the effect |
| of both putting MI in asynchronous mode and making CLI background |
| commands possible. CLI background commands are now always possible |
| “out of the box” if the target supports them. The old spelling is |
| kept as a deprecated alias for backwards compatibility. |
| </p> |
| <p>Even if <small>GDB</small> can accept a command while target is running, |
| many commands that access the target do not work when the target is |
| running. Therefore, asynchronous command execution is most useful |
| when combined with non-stop mode (see <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>). Then, |
| it is possible to examine the state of one thread, while other threads |
| are running. |
| </p> |
| <p>When a given thread is running, MI commands that try to access the |
| target in the context of that thread may not work, or may work only on |
| some targets. In particular, commands that try to operate on thread’s |
| stack will not work, on any target. Commands that read memory, or |
| modify breakpoints, may work or not work, depending on the target. Note |
| that even commands that operate on global state, such as <code>print</code>, |
| <code>set</code>, and breakpoint commands, still access the target in the |
| context of a specific thread, so frontend should try to find a |
| stopped thread and perform the operation on that thread (using the |
| ‘<samp>--thread</samp>’ option). |
| </p> |
| <p>Which commands will work in the context of a running thread is |
| highly target dependent. However, the two commands |
| <code>-exec-interrupt</code>, to stop a thread, and <code>-thread-info</code>, |
| to find the state of a thread, will always work. |
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