"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
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