X-Recipient: archive-cygwin AT delorie DOT com
X-SWARE-Spam-Status: No, hits=-4.6 required=5.0	tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,KHOP_RCVD_TRUST,RCVD_IN_DNSWL_LOW,RCVD_IN_HOSTKARMA_YE
X-Spam-Check-By: sourceware.org
MIME-Version: 1.0
Date: Tue, 4 Sep 2012 14:58:04 +0200
Message-ID: <CAKw7uVgy4qgeqVMk1dRPb=Lr-so5NP3e6XjER=ZGqd+B+MT3ZQ@mail.gmail.com>
Subject: limitations of TLS using GCC's __thread keyword and Cygwin
From: =?UTF-8?Q?V=C3=A1clav_Zeman?= <vhaisman AT gmail DOT com>
To: cygwin AT cygwin DOT com
Content-Type: text/plain; charset=UTF-8
X-IsSubscribed: yes
Mailing-List: contact cygwin-help AT cygwin DOT com; run by ezmlm
List-Id: <cygwin.cygwin.com>
List-Subscribe: <mailto:cygwin-subscribe AT cygwin DOT com>
List-Archive: <http://sourceware.org/ml/cygwin/>
List-Post: <mailto:cygwin AT cygwin DOT com>
List-Help: <mailto:cygwin-help AT cygwin DOT com>, <http://sourceware.org/ml/#faqs>
Sender: cygwin-owner AT cygwin DOT com
Mail-Followup-To: cygwin AT cygwin DOT com
Delivered-To: mailing list cygwin AT cygwin DOT com

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

-- 
VZ

--
Problem reports:       http://cygwin.com/problems.html
FAQ:                   http://cygwin.com/faq/
Documentation:         http://cygwin.com/docs.html
Unsubscribe info:      http://cygwin.com/ml/#unsubscribe-simple