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Date:	Mon, 9 Dec 2013 16:02:17 -0500
From:	Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To:	cygwin AT cygwin DOT com
Subject:	Re: Signal occasionally causes thread inside win32 api to be suspended?
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On Mon, Dec 09, 2013 at 08:59:26PM +0000, Jon TURNEY wrote:
>On 09/12/2013 20:47, Christopher Faylor wrote:
>> On Sun, Dec 08, 2013 at 05:36:16PM +0000, Jon TURNEY wrote:
>>> I don't really understand the intricacies of cygwin signal delivery,
>>> but I see that it can suspend the target thread to determine if it's in
>>> a safe place to deliver the signal (outside a win32 API call).  I think
>>> that sometimes the thread is not correctly resumed.
>>>
>>> This appears to be the cause of been a long-standing problem with the
>>> X.org X server on cygwin, which we work around by disabling
>>> smart-scheduling (no great loss), but I've only just recently
>>> understood enough about the problem to produce a STC.
>>>
>>> If you run the attached for a while, it stops.  According to Process
>>> Hacker, the main thread is in the suspended state, inside ntdll.dll.
>>> e.g.:
>> 
>> I think I have worked around the problem: calling GetModuleName for the
>> address associated with ntdll.dll while the thread is suspended can cause
>> the program (thread?) to hang.
>
>Ah, makes sense.  It's probably deadlocked on the global loader lock, if you
>happen to suspend the thread while it is held.

Probably something like that.  I used to have tests in the code to avoid things
like that for Windows 9x.  Who would have guessed that you could still get into
this state with modern versions of Windows*?

cgf

*This is a rhetorical question.

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