Re: Reprise: 'in out' parameters for functions

["Robert I. Eachus" <rieachus@comcast.net>]

Wojtek Narczynski wrote:

> Another problem of this kind is that the lock owner thread can get
> preempted by the operating system. This is more frequent, but less
> devastating than a page fault.

There are "tricks" to minimize this.  Even if I am programming at system 
independent level, I try to insure that all pages that may be needed 
inside a lock have been referenced outside the lock first.  In a formal 
sense, this won't improve things, but in practice it can make the 
difference between good performance and bad.

The best of all possible worlds is a compiler that wraps protected 
actions in an interrupt-deferred region.  Like all real-time features, 
this is a two-edged sword, but one you have to use in some cases.

> Okay, practitioners speaking, so I will just listen. Should I ask for
> a refunt for "Transaction Processing: Concept and Techniques" by
> J.Gray & A. Reuter? :-)

Theory is important, so is practice.  Without the theory you don't know 
what is and isn't correct in a formal sense.  But in real-time 
programming, too late is just as bad as any other error, and it is an 
emergent property of the whole system.

It is very frustrating to design a race free and deadlock free system, 
then find that to meet the performance requirements you have to violate 
some of the assumptions necessary to make the system deadlock free. 
Yes, you can often go "back to the drawing board" and come up with a 
more complex solution that works and meets the requirements.  But far 
more often, you end up with a solution which is only deadlock free 
because it occasionally aborts lower priority transactions.

-- 

                                           Robert I. Eachus

"The terrorist enemy holds no territory, defends no population, is 
unconstrained by rules of warfare, and respects no law of morality. Such 
an enemy cannot be deterred, contained, appeased or negotiated with. It 
can only be destroyed--and that, ladies and gentlemen, is the business 
at hand."  -- Dick Cheney