Date: Fri, 22 Jan 1999 12:19:49 -0600 From: "Richard Seaman, Jr." <dick@tar.com> To: "Kurt D. Zeilenga" <Kurt@OpenLDAP.Org> Cc: freebsd-current@FreeBSD.ORG Subject: Re: -D_REENTRANT (Was: Using LinuxThreads) Message-ID: <19990122121949.I92540@tar.com> In-Reply-To: <36A8BA23.8AE3B430@OpenLDAP.Org>; from Kurt D. Zeilenga on Fri, Jan 22, 1999 at 09:49:23AM -0800 References: <Pine.BSF.4.05.9901182203500.11971-100000@janus.syracuse.net> <19990119024539.A88383@top.worldcontrol.com> <19990119140613.B826@shale.csir.co.za> <19990119091151.F600@tar.com> <19990121181228.A98581@shale.csir.co.za> <3.0.5.32.19990121114214.00958c30@localhost> <19990121143940.D5495@tar.com> <36A7A395.29B3E8A7@OpenLDAP.Org> <19990122114153.H92540@tar.com> <36A8BA23.8AE3B430@OpenLDAP.Org>
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On Fri, Jan 22, 1999 at 09:49:23AM -0800, Kurt D. Zeilenga wrote: > "Richard Seaman, Jr." wrote: > > _THREAD_SAFE is only used in stdio.h. Looking at what's there, it could > > be rewritten to eliminate _THREAD_SAFE entirely, at a (very slight) > > performance penalty. You'd have to check __isthreaded (could be done > > once, instead of twice, as in the code now) each time you call one > > of the functions defined within the _THREAD_SAFE switch. All > > _THREAD_SAFE does is let you avoid checking __isthreaded when you're > > not threaded. > > So, if I want to produce a library which can be safely used by both > threaded and non-threaded applications I should NOT define -D_THREAD_SAFE > such that __isthreaded is always checked by the library. I guess I was a little unclear. 1) I think you would have to rewrite a little bit of the header to use the __isthreaded test on a couple of more functions. 2) If you always define -D_THREAD_SAFE, __isthreaded will be checked whether you're threaded or not. If you're not threaded, __isthreaded should be false and you avoid the file locking code. If you're threaded, __isthreaded should be true and you get the file locking (if you're linked with a library that has actualy file locking code to override the libc file locking stub functions -- libc_r does this for you, you need something like a pthreads library linked in for libc). You could also just eliminate _THREAD_SAFE entirely by letting __isthreaded get checked on each relevant call. 3) If you're linking with FreeBSD user threads, you still have the problem that user threads needs libc_r and not libc, while everything else (no threads, or kernel threads) needs libc. The _THREAD_SAFE switch doesn't affect whether you link with libc or libc_r. As mentioned before, libc_r could be rewritten to look like a "normal" libpthread addon library, ie. it wouldn't duplicate libc, but it would require some work. 4) There are portions of libc that are only thread safe when they are compiled as part of libc_r (almost all of libc gets rolled into libc_r). This can be fixed. Indeed, I have patches that do this, but they need some testing. -- Richard Seamman, Jr. email: dick@tar.com 5182 N. Maple Lane phone: 414-367-5450 Chenequa WI 53058 fax: 414-367-5852 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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