[Lazarus] Strange dependency of units

[Michael Van Canneyt]

On Thu, 5 Apr 2012, Michael Schnell wrote:

> On 04/05/2012 03:39 PM, Michael Van Canneyt wrote:
>> Events do not automagically appear in your application, even under windows.
>> 
>> They are not interrupts.
>
> AFAIK, in Windows, the Application main thread can call an API function to 
> wait for the next message.

Exactly. That is called 'polling' windows...

> Here it uses no CPU cycles and when a message in 
> the queue for that thread arrives from what origin ever, the thread is 
> activated at once and will run according to it's priority thus minimizing the 
> latency to the limit that the OS and the other running tasks allow. I don't 
> see why a "timeout" would necessarily be enabled to return from that call 
> (providing real polling), as there should be no notifications to the main 
> thread that don’t run through the queue, generating such a message and waking 
> the Main Thread.
>
> Of course if the main thread is just working on an event, when a new event is 
> fed to the queue, it will first finish its current work (unless it explicitly 
> calls "Application.ProcessMessages") before it is ready to handle the new 
> event. But this is just how a single-threaded application needs to work.
>
> I would not call this "polling", as the "main Loop" only runs at max a single 
> turn for each event, while the process sleeps until the next event arises.

You have a strange definition of polling.

Polling = Checking something at regular intervals.

No more, no less.

Whether or not the CPU is used a lot, or how many threads are in the
application, is irrelevant for the definition, they are implementation
details.

> Maybe GTK does not allow for such a design, though, because not all events 
> can be run though a single queue with embedded waiting/waking functionality.

Qt/GTK/X11 allow for this design as well.

Michael.