[PATCH 01/15] server: Wait before suspending threads in APC.

[Rémi Bernon]

On 1/27/20 10:58 PM, Jacek Caban wrote:
> Hi Rémi,
> 
> 
> On 27/01/2020 13:07, Rémi Bernon wrote:
>> The APC_BREAK_PROCESS call creates a thread that raises an exception,
>> suspending the whole process. There's a race condition between this
>> thread and the APC thread notifying the server of its completion.
> 
> 
> What's wrong about that? Suspending process on thread creation shouldn't 
> be a problem. The debugger should process this event, which will resume 
> the new thread and let it continue to the break point. Before 
> introducing APC_BREAK_PROCESS I had to fix it in another place in 
> winedbg, see commit 1bb98982d682a85b82e, maybe there is similar problem 
> in gdb proxy?
> 
> 
> Thanks,
> 
> Jacek
> 

In gdbproxy mode, winedbg calls DebugBreakProcess whenever Ctrl-C is 
pressed, then WaitForDebugEvent for the corresponding event.

However *sometimes* DebugBreakProcess never returns and it cannot wait 
for the event and process it unless it is done in another thread -which 
would require changes in gdbproxy I would rather avoid. That may be how 
winedbg works in frontend mode?

The reason why DebugBreakProcess sometimes returns but not always is 
that it requests the APC, which completion notification is sometimes 
received by the server before the exception is raised and all threads 
are suspended, but sometimes it isn't. I don't think this was intended, 
and it would probably be better if DebugBreakProcess returns -or not- in 
a consistent way.
-- 
Rémi Bernon <rbernon at codeweavers.com>