[Lldb-commits] [lldb] [lldb-dap] Fix raciness in launch and attach tests (PR #137920)

[Jonas Devlieghere via lldb-commits]

JDevlieghere wrote:

> Someone once told me: "Whatever problem you're trying to solve, if you're using atomics, now you've got two problems."
> 
> I can't say I've always followed that advice, but I do think that atomics are rarely the right solution to a problem. And I think this is a good example of that.
> 
> What you want is not to suppress _a_ event (whatever it might be). You want to suppress a very specific event (that is supposed to be generated by the action you're about to perform). That means that something needs to ensure that the other thread reads this flag after you've generated the event. If that's true, then you already have a happens-before relationship and the atomic is not necessary. If it isn't (there is no happens-before), then the atomic will not help.

You're right. I have an implementation that used a mutex but it made the same mistake I have here with the atomic. Luckily that's easily solvable by putting the code that generates the stop and consumes the stop in the critical section. 

> That said, why is ConnectRemote generating a stopped event in synchronous mode? Maybe that's the bug we should fix?

That's a long standing bug that comes up about once or twice a year. I spend some time looking into that at some point, but it's so long ago that I don't remember what the  blocker was. That said, solving that isn't sufficient for the problem at hand, since we need to solve the asynchronous case as well. 


https://github.com/llvm/llvm-project/pull/137920