[Proj] libproj4 thread safety

[Glynn Clements]

Gerald Evenden wrote:

> OK, I think I understand it except for the detail below.
> 
> On Apr 22, 2005, at 6:03 PM, Glynn Clements wrote:
> 
> > 	....
> file pj_error_stuff.c
> #include <pthread>
> 
> // lot'sa stuff
> > 	
> > 	static int *proj_errno_location(void)
> > 	{
> > 	  void *p;
> > 	  pthread_once(&proj_errno_key_once, proj_errno_key_create);
> > 	  p = pthread_getspecific(proj_errno_key);
> > 	  if (!p) {
> > 	    p = malloc(sizeof(int));
> > 	    pthread_setspecific(proj_errno_key, p);
> > 	  }
> > 	  return (int *) p;
> > 	}
> >
> end of pj_error_stuff file.
> 
> You have the local (static) routine above which seems straight forward
> and the global one below.
> 
> It would seem that if I put the above in a file (eventually for the 
> library)
> that the above routine should be global and executed safely in any
> thread.  And, I might add, transparently to the using programmer.
> That is, like an errno call.  The 'define' would be part of the 
> lib_proj.h.

Exactly.

> > 	int *proj_errno_location(void)
> > 	{
> > 	  return (int *) pthread_getspecific(proj_errno_key);
> > 	}
> >
> I do not understand the inclusion of above procedure other than it 
> eliminates
> a few checks and setup and thus cannot be used as a first call.
> 
> Am I missing something?  (probably so ;-( )

No, I didn't do a final quality-control pass on my message.

The static proj_errno_location() was originally intended to be an
initialisation function, to be called from the exported
proj_errno_location(). Then I merged the two, and forgot to delete the
second one and forgot to remove the "static" from the first.

-- 
Glynn Clements <glynn at gclements.plus.com>