Date: Fri, 22 Jan 1999 09:49:23 -0800 From: "Kurt D. Zeilenga" <Kurt@OpenLDAP.Org> To: "Richard Seaman, Jr." <dick@tar.com> Cc: freebsd-current@FreeBSD.ORG Subject: Re: -D_REENTRANT (Was: Using LinuxThreads) Message-ID: <36A8BA23.8AE3B430@OpenLDAP.Org> References: <19990119091151.F600@tar.com> <19990118182717.A15566@top.worldcontrol.com> <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>
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"Richard Seaman, Jr." wrote: > > On Thu, Jan 21, 1999 at 02:00:53PM -0800, Kurt D. Zeilenga wrote: > > > > For kernel threading you just use libc. Whether or not libc generates > > > thread safe (re-entrant) calls depends on whether its also linked with > > > a library that 1) sets __isthreaded to a non-zero value, 2) has a _spinlock() > > > implementationm, and 3) implements the functions flockfile, funlockfile, etc. > > > There are also a few macros in header files that require _THREAD_SAFE to > > > be defined to be thread safe. > > > > > > I was hoping to be able to produce one ldap library that could be safely > > linked with or without threads. However, if I must define _THREAD_SAFE > > to generate code to be linked with threads then I must produce two libraries > > (-lfoolib compiled with -U_THREAD_SAFE and -lfoolib_r with -D_THREAD_SAFE). > > _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. In effect, -D_THREAD_SAFE makes the generated code non-thread UNSAFE. - Kurt To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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