limitations of TLS using GCC's __thread keyword and Cygwin

[Václav Zeman]

On 09/04/2012 04:39 PM, Ryan Johnson wrote:
> On 04/09/2012 8:58 AM, Václav Zeman wrote:
>> Hi.
>>
>> I am am porting a library that can use the __thread keyword in its
>> internals to provide thread local storage. Now, with MSVC there is a
>> limitation on pre-Vista Windows (see [1]) that DLLs using
>> __declspec(thread) (MSVC equivalent of GCC's __thread) cannot be
>> loaded using LoadLibrary() because pre-Vista Windows allocate the TLS
>> declared that way only on process startup. Vista and later Windows do
>> not seem to have the limitation. Since Cygwin officially still
>> supports at least Windows XP, I want to provide a library that works
>> there as well.
>>
>> Does Cygwin's GCC and its TLS emulation work around this problem? IOW,
>> are Cygwin DLLs using TLS declared using __thread keyword safe to be
>> loaded using LoadLibrary()/dlopen() or are they not safe to be loaded
>> that way?
>>
>> [1] http://msdn.microsoft.com/en-us/library/2s9wt68x.aspx
>>
> I suspect it's not a problem, but if I were you I'd write a simple
> test program to see. Unfortunately, TLS in general seems broken on my
> machine when I tried it, but that might be due to my home-brew gcc
> being configured wrong or something.
I would have done that already but I do not have any Windows XP machine
to try this on.

-- 
VZ


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