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Date:	Wed, 10 Mar 2010 10:12:52 -0500
From:	Christopher Faylor <cgf-use-the-mailinglist-please AT cygwin DOT com>
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Subject:	Re: Cygwin 1.7: Concurrency Issue with Shared State Initialization
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On Wed, Mar 10, 2010 at 10:59:29AM +0100, Corinna Vinschen wrote:
>On Mar 10 10:55, Schmidt, Oliver wrote:
>> Hi Corrina,
>> 
>> Thanks for your involvement :-)
>> 
>> >> [...] a spinlock [...] With
>> >> InterlockedCompareExchange() and Sleep() it should be quite simple to
>> >> create one that's very efficient in the usual scenario.
>> 
>> > Does the below patch fix this for you?
>> 
>> I'll test the snapshot asap!
>> 
>> [...]
>> +      LONG init = InterlockedCompareExchange (&installation_root_init, 1L, 0L);
>> [...]
>> +	  low_priority_sleep (0);
>> [...]
>> 
>> I see we were thinking along the same lines ;-)
>
>The final patch is from cgf.  It's probably more performant since it
>drops the requirement for an additional spinlock.

The snapshot contains try #3 on getting the locking right.  I had to scrap
my approach after Corinna politely reminded me that I had done something
stupid in the prior snapshot.

But, the spinlock approach was nothing new.  We use that technique in
several places in Cygwin.

cgf

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