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27.1.2 Asynchronous command execution and non-stop mode

On some targets, gdb is capable of processing MI commands even while the target is running. This is called asynchronous command execution (see Background Execution). The frontend may specify a preferrence for asynchronous execution using the -gdb-set target-async 1 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 -list-target-features command.

Even if gdb 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 Non-Stop Mode). Then, it is possible to examine the state of one thread, while other threads are running.

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 print, set, 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 ‘--thread’ option).

Which commands will work in the context of a running thread is highly target dependent. However, the two commands -exec-interrupt, to stop a thread, and -thread-info, to find the state of a thread, will always work.