Why does thread support depend on GLX_DIRECT_RENDERING in libGL?

Keith Packard keithp at keithp.com
Thu Apr 14 09:35:09 PDT 2005

On Thu, 2005-04-14 at 09:07 -0700, Ian Romanick wrote:
> While working on bug #3024, I noticed something kind of odd.  Every 
> place where there is code that depends on XTHREADS being defined, it 
> also depends on GLX_DIRECT_RENDERING being defined.  The net result 
> being that the only time you get thread safety in libGL (i.e., a GLX 
> context per thread) is when GLX_DIRECT_RENDERING is defined.  This seems 
> wrong.

As an aside -- there's a way to detect XTHREADS support in the local
Xlib so that libGL can be built correctly if you like.

I use the following snippet in various configure.ac files:

        AC_MSG_CHECKING([for XTHREADS in Xlib])
           [AC_LANG_PROGRAM([[#include <X11/Xlib.h>]],
                            [[return XInitThreads() == 0 ? 0 : 1;]])],


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