Intermittent failures retrieving process exit codes - snapshot test requested

[Tom Honermann]

On 12/21/2012 05:23 PM, marco atzeri wrote:
> On 12/21/2012 8:36 PM, Christopher Faylor wrote:
>> I tested this lightly on Windows 7 and 32-bit XP but it would be nice to
>> hear if multi-threaded things like X work on other platforms too.
>>
>> If you test a snapshot, note that I'm still tracking down Ken Brown's
>> reporte emacs regression in recent snapshots so that will still be
>> broken.
>>
>> cgf
>>
>
> I think the Xserver doesn't like it.
> on 20121221 it freezes on start on W7/64
> no issue on 20121218

I was worried about this possibility after looking at the code changes. 
  But, I haven't had to a chance to test adequately yet.  I would expect 
indefinite blocking in dll_entry() may prevent unloading DLLs.  For 
example, calls to dll_entry() for DLL_PROCESS_DETACH may get blocked.

It looks to me like the changes made are insufficient to prevent the 
race.  For example, this won't address the case where an exiting thread 
releases the process lock acquired in dll_entry() before a thread 
exiting the process acquires it in pinfo::exit().  Both threads could 
still end up in an ExitThread() vs ExitProcess()/TerminateProcess() 
race.  However, this is only true for threads whose exits are not 
predicated upon an action taken by the process exiting thread after it 
has acquired the process lock in pinfo::exit().  And since the exiting 
thread must be the last thread of the process in order to hit the issue, 
this may not be a concern.

I'm not sure that a general workaround for this issue is feasible for 
all possible threads.  At least, not without hooking the Terminate* and 
Exit* Win32 APIs.  My gut tells me that a general solution requires 
waiting for thread handles to be signaled, but I haven't thought it 
completely through yet.

It looks like Chris reverted the change and checked in a new update.  I 
haven't looked at those changes yet.

Tom.


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