labath added a comment.

In D129814#3654276 <https://reviews.llvm.org/D129814#3654276>, @jasonmolenda 
wrote:

> In D129814#3654230 <https://reviews.llvm.org/D129814#3654230>, @labath wrote:
>
>> Generally, this makes sense to me, but I do have one question (not 
>> necessarily for Jim). These tests work on (arm) linux, and I am wondering 
>> why is that the case. Could it be related to the fact that lldb-server 
>> preserves the stop reason for threads that are not running? I.e. if we have 
>> two threads hit a breakpoint (or whatever), and then step one of them, then 
>> the other thread will still report a stop_reason=breakpoint. Do you know if 
>> this is supposed to happen (e.g. does debugserver do that)?
>
> I'd have to go back and test it to be 100% sure but from the behavior I see 
> on Darwin systems, when we receive a watchpoint hit on two threads at the 
> same time, and instruction-step the first thread, when we ask debugserver for 
> the current stop-reason on thread two, it says there is no reason.  The 
> watchpoint exception on the second thread is lost.  I could imagine 
> lldb-server behaving differently. (I think when we fetch the mach exceptions 
> for the threads, they've now been delivered, and when we ask the kernel for 
> any pending mach exceptions for the threads a second time -- even if those 
> threads haven't been allowed to run, I think the state is lost, and 
> debugserver didn't save that initial state it received.)

Yes, that sounds plausible. It lldb-server (on linux) it happens differently 
because we store each stop reason inside the thread object, and since we can 
control each thread independently, there's no reason to touch it if we're not 
running the thread. Although it also wouldn't be hard to clear in on every 
resume.

So which one of these behaviors would you say is the correct one?


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