[lldb-dev] Race condition crashes during launching LLDB

[Pavel Labath via lldb-dev]

On 5 February 2016 at 05:09, Jeffrey Tan via lldb-dev
<lldb-dev at lists.llvm.org> wrote:
> After adding some logging I figured out that the race condition is caused by
> process.Continue() did not guarantee process has been really resumed yet in
> async mode, so the second wait_for_process_stop() is skipped immediately to
> kill listener thread and destroying debugger. I know I have a race condition
> bug here because of polling for process state, but why is lldb crashing when
> listener thread has exited and SBDebugger.Destroy() is called? What is the
> situation that SBDebugger.Destroy() can be called safely?

My guess on the sequence of events here is this:
- call process.Continue(), which returns immediately
- you check process.is_stopped, which is still true
- set self.should_quit = true
- listener thread exits and you join in
- you call SBDebugger.Destroy()

all of this happens _before_ the process has had a chance to really
start. So now Destroy starts destroying the process while it is just
being started up and things go south. It could be argued that this is
a bug in LLDB (this is the reason our TestEvents is disabled). I've
been investigating this a bit, but it did not look easy.

In any case, what you can do now is to make sure you wait for the
eStateRunning event before you try to do anything to the process
(including killing it). These paths are more tested and they I believe
they should be stable.

pl