Re: Messaging question [was: Is this expected behavior or not]

["Randy Brukardt" <randy@rrsoftware.com>]

"Shark8" <onewingedshark@gmail.com> wrote in message 
news:09f2e5f7-84fe-419b-b27d-207e697c8e46@googlegroups.com...
> On Friday, March 29, 2013 6:49:25 PM UTC-6, Randy Brukardt wrote:
>>
>>
>> Claw uses hidden operations on window objects to keep the mechanisms of 
>> the
>> message loop hidden away.
>
> Very tangentially on this; what do you see would be the consequence of a 
> system
> using a loop over a select [for messaging] -- or would it be any 
> different?
>
> I'm really fuzzy on my low-level windows programming and, after reading 
> this
>( 
>http://forums.codeguru.com/showthread.php?449338-Windows-message-loop-efficiency ) 
>,
>I found myself wondering; since you wrote CLAW I thought I'd ask.

The reason we hid the loop had to do with correctness more than efficiency. 
When you explicitly allow fooling with all of that loop mechanism, it's 
impossible to build anything on top of it and have any hope that it works 
right, because you're relying on the client to use the object exactly the 
right way, or it won't work (nor will it give any indication of what you did 
wrong).

In any case, there is *always* a loop inside the application; the question 
in the thread mentioned above is how the loop is written. You get dozens of 
messages for typical actions in an Windows program; you need a loop to 
process them all. I believe we did our waiting at the Ada level, rather than 
the Windows level, because that prevented locking up the Windows 
program/thread while waiting for something to happen. We use Ada delays to 
release the CPU if we don't have anything to do (that way, the Ada runtime 
knows about the blocking and can schedule other work if appropriate). Again, 
performance had nothing to do with it, we didn't want to assume a particular 
Ada runtime model (that is, how tasks are mapped to threads). We tuned the 
performance after making these choices.

                                     Randy.