X-Recipient: archive-cygwin AT delorie DOT com X-SWARE-Spam-Status: No, hits=-5.3 required=5.0 tests=AWL,BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FROM,KHOP_RCVD_TRUST,KHOP_THREADED,RCVD_IN_DNSWL_LOW,RCVD_IN_HOSTKARMA_YE X-Spam-Check-By: sourceware.org MIME-Version: 1.0 In-Reply-To: <20120904215129.GA30731@ednor.casa.cgf.cx> References: <504612A3 DOT 6070605 AT cs DOT utoronto DOT ca> <50466981 DOT 70005 AT gmail DOT com> <20120904215129 DOT GA30731 AT ednor DOT casa DOT cgf DOT cx> Date: Wed, 5 Sep 2012 10:05:33 +0200 Message-ID: Subject: Re: limitations of TLS using GCC's __thread keyword and Cygwin From: =?UTF-8?Q?V=C3=A1clav_Zeman?= 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 Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: cygwin-owner AT cygwin DOT com Mail-Followup-To: cygwin AT cygwin DOT com Delivered-To: mailing list cygwin AT cygwin DOT com 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. -- 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