On 4 September 2012 23:51, Christopher Faylor wrote: > On Tue, Sep 04, 2012 at 10:50:09PM +0200, V??clav Zeman wrote: >>On 09/04/2012 04:39 PM, Ryan Johnson wrote: >>> On 04/09/2012 8:58 AM, V??clav 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. > > I don't believe that __thread is implemented on Cygwin. Adjust your beliefs. :) It is implemented and it works correct as far as I can tell. It implements TLS using calls to __emutls* routines. What I am unclear about is whether the implemention works around the limitation mentioned in the MSDN link or not.
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