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Date:	Tue, 4 Sep 2012 14:58:04 +0200
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Subject:	limitations of TLS using GCC's __thread keyword and Cygwin
From:	=?UTF-8?Q?V=C3=A1clav_Zeman?= <vhaisman AT gmail DOT com>
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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

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