How to switch between threads to see their variables and frames?

[vatosarmat]

Hello. I am debugging Rust application which does thread::spawn. When application stops on a breakpoint I can examine .scopes and .frames of the current thread. But how to examine .scopes and .frames of other threads?

[theHamsta]

At the moment nvim-dap only supports a single stopped thread. This means that you can currently only inspect the variables of the current thread. dap-ui also fetches a snapshot of the frames other running threads.

Stopping all threads to inspect their variables, would require a refactoring to support multiple stopped threads. Then, the .pause command you be used in stopped state to stop additional threads or all threads could be paused automatically after the first one hits a breakpoint.

[vatosarmat]

Thanks for reply! Unfortunately, I can't mark it as answer because of some glitch either with my browser or with GitHub frontend 😕

[drum-computer]

Hey! I was just wondering, is it still the case in 2024? And if it is, can you please point me in the direction of what has to be changed in the code, I would be interested in contributing this feature potentially.

[mfussenegger]

I think even back in 2021 nvim-dap already allowed stopping multiple threads, but it's locked behind a setting because it can be confusing if non-visible threads get blocked by a breakpoint.

You can set:

require("dap").defaults.fallback.auto_continue_if_many_stopped = false

To allow multiple threads to get stopped.

After that you can switch between the thread's active frame via the threads widget. E.g. either .threads in the REPL, expand the thread with <CR>, then select the frame with <CR> or the same but via require("dap.ui.widgets").centered_float(require("dap.ui.widgets").threads)

After the frame is selected, evaluating the variable should show you the right value.