The debugger command doesn't seem to work when using multiple threads at the same time.

[thijsnado]

Your environment

• ruby -v: 3.2.2
• rdbg -v: 1.8.0

Describe the bug

Doesn't seem to work well with multithreaded debugger statements. The program does not print out expected local variables and seems to hang forever after last continue statement.

To Reproduce

Given the following ruby code:

require "debug"

thr1 = Thread.new {
  hello = "world"

  debugger

  puts hello
}


thr2 = Thread.new {
  hello = "hello"

  debugger

  puts hello
}

thr1.join
thr2.join

The first time I reach a breakpoint it shows me in the hello = "hello" block. When I type out hello though it than jumps me to hello = "world" block. After typing out hello a second time, it prints out the string "hello" instead of "world". If I type continue it hangs forever after that. If I run the program without the debugger statements it doesn't hang.

Expected behavior I would expect debugger to be somewhat threadsafe. Obviously debugger cannot necessarily control the order of these two debuggers. The second debug statement may execute first but I'd expect that the breakpoint would match the local variable and I'd expect typing continue would than make the program keep running and go to the next debugger statement or terminate the program if no more debugger statements.

[ko1]

Thank you. This code is great to reproduce the issue. Honestly speaking current thread management is not strict and this is a time to consider strict management...

[ko1]

I couldn't complete to solve this issue so I'll try it on 1.9.1

[sammyhenningsson]

I can't continue after hitting a breakpoint with Puma and I believe this might be the same issue. Just curious.. Is it a known issue that debug can't be used with puma due to this? Or am I doing something else wrong? (I've tried and failed on several rails projects. Changing to webrick makes it work)