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Date: Mon, 7 Jan 2013 01:43:17 -0500
From: Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
To: cygwin AT cygwin DOT com
Subject: Re: pthread_rwlock_tryrdlock bug (with test & patch)
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On Sun, Jan 06, 2013 at 06:24:47PM +0100, Antti Kantee wrote:
>[I'd submit this to cygwin-patches, but the web page says only 
>subscribers can post to that list, so please bear with me for this 
>simple issue]
>
>Hi,
>
>Calling pthread_rwlock_tryrdlock() twice from the same thread always 
>fails with EBUSY the second time.  See attached test.c.  Replacing the 
>second tryrdlock() with rdlock() makes the call succeed, leading me to 
>believe there is a bug in tryrdlock().
>
>Assuming I was looking at the correct source file, the attached patch 
>should fix the issue.  I'm not sure why the lookup_reader() call was 
>there in the first place; perhaps a remnant from a time when recursive 
>read locking was not supported?
>
>While looking at tryrdlock(), the handling of ULONG_MAX also seems 
>wrong, as you'd probably want to return EAGAIN instead of allocating 
>another reader structure.  However, that problem is arguably more of an 
>academic issue and therefore I didn't touch it in my patch.

Thanks for the analysis and patch.  I've made a few more changes to this
function and should have everything checked in tomorrow.

cgf

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