Re: GCIC Fullscreen applications

OK, understand that. But I hadn't seen that kind of thing going on in pdpclib. Maybe I need to check the source more carefully!


--- In [email protected], Ivan Warren <ivan@...> wrote:
>
> mfnoel wrote:
> > I rely mostly on testing, but could you elaborate a bit on how reentrancy is a problem when recursion is OK? Want to know what to stay away from...
> > 
> 
> Well..
> 
> I think because a function or module can be recursive without being 
> reentrant.
> 
> ***************
> char foo[10];
> 
> int bar(char x)
> {
> 	static char	z[2];
> 	if(x!=0)
> 	{
> 		foo[0]=0;
> 		z[0]=x;
> 		z[1]=0;
> 	}
> 	if(strlen(foo)==(sizeof(foo)-1)) return 0;
> 	strcat(foo,z);
> 	return bar(0);
> }
> ***************
> 
> That's recursive, but not reentrant. If the task becomes interrupted and 
> another task with another context invokes bar(), then unexpected results 
> will occur - because both the external symbol "foo" and the internal "z" 
> are shared between multiple contexts.
> 
> Task 1 invokes bar("A").. Expects foo to be a bunch of 'A's..
> Task 1 is interrupt midflight
> Task 2 invokes bar("B") and the function completes
> Task 1 resumes and bar() completes. foo contains a bunch of 'B's
> 
> Of course, the example is totally trivial and useless - it's just an 
> example.
> 
> So, to stay away from the "problem" :
> 
> - Keep information in task owned contexts (a stack or a chained list of 
> buffers and registers)
> - Serialize access to shared resources (lock/unlock mechanism for example).
> 
> --Ivan
>