Incorrect handling of exited threads in debugger

[EvilBeaver]

Bug Description:

If debug thread is exited it does not removed from the threads panel till next stop and Threads request to debug adapter.
This leads to incorrect display and sometimes to broken debugger behavior.

Steps to Reproduce:

1. launch debugger of some language with debug adapter
2. See that no threads shown, only session
3. stop at breakpoint
4. continue to thread exit
5. see that threads panel still shows thread in a Running state

Expected: no running threads shown, showing Session only, as it was at very beginning.
Things are getting worse if there's multiple stopped threads and they all continued to the exit.

On the picture Thread 24 already exited and not running.
Expected that threads panel looks like this when no debuggable threads available

Additional Information

It seems it should be fixed here https://github.com/eclipse-theia/theia/blob/master/packages/debug/src/browser/debug-session.tsx#L912, need to remove thread from this._threads on thread exited.

• Operating System: any
• Theia Version: cloned from master

[vince-fugnitto]

@EvilBeaver do you happen to have additional details to consistently reproduce the bug?
I've tried with node debugging (ex: run mocha tests) and the threads view is correctly cleared on exit.

[EvilBeaver]

To reproduce this, you'll need to have no threads debugged (all exited), but debug session still active. I suppose it's hard to achieve in node.js, cause it's usually single threaded and all threads exit also means session exit.

[alvsan09]

I have tried to reproduce this issue using multiple threads spawned by the following 'javascript' program,
you can launch this program multiple times and see how the threads get cleared as expected.

the following recording shows the execution:
https://user-images.githubusercontent.com/76971376/236262803-4790db9b-7ec3-4ea7-a55c-d242033019b9.mp4

Any additional ideas on how to reproduce this issue are very welcome !

const { spawn } = require('child_process');

const numberOfThreads = 5;
const threadDuration = 5000;
const createInterval = 1000;

function spawnThread() {
    const child = spawn('node', ['-e', `setTimeout(() => {}, ${threadDuration});`]);
    child.on('spawn', () => {
        console.log(`Thread ${child.pid} created`);
    });
    child.on('close', () => {
        console.log(`Thread ${child.pid} exited`);
    });
}

let threadsSpawned = 0;
const intervalId = setInterval(() => {
    spawnThread();
    threadsSpawned++;
    if (threadsSpawned === numberOfThreads) {
        clearInterval(intervalId);
    }
}, createInterval);

[EvilBeaver]

@alvsan09 I don't know how to reproduce this in node debugger. I'm writing a debug adapter for another language. Here's a code line with a problem: https://github.com/eclipse-theia/theia/blob/master/packages/debug/src/browser/debug-session.tsx#L912 nobody deletes a thread from _threads collection, thus last exited thread does not get removed from threads panel.

In your example you need to have spawning.js exited, but session still active. This can't be achieved in current node.js debugger