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Message-ID:	<52A62F2E.8040908@dronecode.org.uk>
Date:	Mon, 09 Dec 2013 20:59:26 +0000
From:	Jon TURNEY <jon DOT turney AT dronecode DOT org DOT uk>
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To:	cygwin AT cygwin DOT com
Subject:	Re: Signal occasionally causes thread inside win32 api to be suspended?
References:	<52A4AE10 DOT 8080303 AT dronecode DOT org DOT uk> <20131209204759 DOT GA1675 AT ednor DOT casa DOT cgf DOT cx>
In-Reply-To:	<20131209204759.GA1675@ednor.casa.cgf.cx>

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.

> This should be rectified in today's snapshot.

-- 
Jon TURNEY
Volunteer Cygwin/X X Server maintainer

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