Experimental Physics and
Industrial Control System

Jeff Hill <[email protected]> · Thu, 12 Mar 1998 10:12:26 -0700

>  Is it even guaranteed for the simpler line
> 
> 	vxvar = pao->val;
> 
> where vxvar is a globally visible variable of type double?

I agree that it would not be a good idea to assume so in a portable source code.
I will still argue that a mutex semaphore should be used in favor of intLock()/intUnlock()
in task level code. Even if the locking interval is currently quite short, you or some
other developer who may not be as keen on these issues will invariably
need to expand the amount of code in-between the lock calls. I hope that
this person, despite schedule and time pressures, is conscientious and therefore is
willing to write the additional code require to initialize and use the mutex semaphore.
I am also concerned about what would happen to the system if for any reason
an exception was generated (say a floating point exception or a bus error) while 
intLock() is applied. On some architectures a floating point exception can occur
when loading an invalid floating point number. The key difference is that intLock()
is a global operation with side effects on the entire system, and semTake() will only 
have side effects on tasks using the mutex semaphore. It is much easier to 
understand (and predict the failure modes of ) a system that is made up of smaller 
components that minimize their global side effects.

Jeff

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System