109 lines
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109 lines
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<title>Asynchronous and non-stop modes - Debugging with GDB</title>
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<link rel="up" href="GDB_002fMI-General-Design.html#GDB_002fMI-General-Design" title="GDB/MI General Design">
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<div class="node">
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<a name="Asynchronous-and-non-stop-modes"></a>
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<a name="Asynchronous-and-non_002dstop-modes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Thread-groups.html#Thread-groups">Thread groups</a>,
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Previous: <a rel="previous" accesskey="p" href="Context-management.html#Context-management">Context management</a>,
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Up: <a rel="up" accesskey="u" href="GDB_002fMI-General-Design.html#GDB_002fMI-General-Design">GDB/MI General Design</a>
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</div>
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<h4 class="subsection">27.1.2 Asynchronous command execution and non-stop mode</h4>
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<p>On some targets, <span class="sc">gdb</span> is capable of processing MI commands
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even while the target is running. This is called <dfn>asynchronous
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command execution</dfn> (see <a href="Background-Execution.html#Background-Execution">Background Execution</a>). The frontend may
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specify a preferrence for asynchronous execution using the
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<code>-gdb-set mi-async 1</code> command, which should be emitted before
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either running the executable or attaching to the target. After the
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frontend has started the executable or attached to the target, it can
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find if asynchronous execution is enabled using the
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<code>-list-target-features</code> command.
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<dl>
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<dt><code>-gdb-set mi-async on</code><br><dt><code>-gdb-set mi-async off</code><dd>Set whether MI is in asynchronous mode.
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<p>When <code>off</code>, which is the default, MI execution commands (e.g.,
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<code>-exec-continue</code>) are foreground commands, and <span class="sc">gdb</span> waits
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for the program to stop before processing further commands.
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<p>When <code>on</code>, MI execution commands are background execution
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commands (e.g., <code>-exec-continue</code> becomes the equivalent of the
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<code>c&</code> CLI command), and so <span class="sc">gdb</span> is capable of processing
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MI commands even while the target is running.
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<br><dt><code>-gdb-show mi-async</code><dd>Show whether MI asynchronous mode is enabled.
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</dl>
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<p>Note: In <span class="sc">gdb</span> version 7.7 and earlier, this option was called
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<code>target-async</code> instead of <code>mi-async</code>, and it had the effect
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of both putting MI in asynchronous mode and making CLI background
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commands possible. CLI background commands are now always possible
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“out of the box” if the target supports them. The old spelling is
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kept as a deprecated alias for backwards compatibility.
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<p>Even if <span class="sc">gdb</span> can accept a command while target is running,
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many commands that access the target do not work when the target is
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running. Therefore, asynchronous command execution is most useful
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when combined with non-stop mode (see <a href="Non_002dStop-Mode.html#Non_002dStop-Mode">Non-Stop Mode</a>). Then,
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it is possible to examine the state of one thread, while other threads
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are running.
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<p>When a given thread is running, MI commands that try to access the
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target in the context of that thread may not work, or may work only on
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some targets. In particular, commands that try to operate on thread's
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stack will not work, on any target. Commands that read memory, or
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modify breakpoints, may work or not work, depending on the target. Note
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that even commands that operate on global state, such as <code>print</code>,
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<code>set</code>, and breakpoint commands, still access the target in the
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context of a specific thread, so frontend should try to find a
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stopped thread and perform the operation on that thread (using the
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‘<samp><span class="samp">--thread</span></samp>’ option).
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<p>Which commands will work in the context of a running thread is
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highly target dependent. However, the two commands
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<code>-exec-interrupt</code>, to stop a thread, and <code>-thread-info</code>,
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to find the state of a thread, will always work.
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</body></html>
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