[Live-devel] Question about BasicUsageEnvironment/BasicTaskScheduler

[Ross Finlayson]

>I downloaded the library source (from December 15th if I remember
>right). I have been going through the code trying to figure out how
>stuff works. I noticed that there is another version of
>BasicUsageEnvironment and BasicTaskScheduler: BasicUsageEnvironment0
>and BasicTaskSchedule0. I also noticed that only BasicTaskScheduler0
>has a definition for the function "doEventLoop". May I know why there
>are 2 versions? How are the 2 used?

"BasicTaskScheduler" is implemented using "BasicTaskScheduler0" (its parent 
class).  Note that "BasicTaskScheduler0" is an abstract class; you can use 
it only by defining a subclass.  Similarly, "BasicTaskScheduler0" is 
implemented using "TaskScheduler" (its parent class), which is also an 
abstract class.

The reason for implementing "BasicTaskScheduler" this way is to allow for 
the possibility of defining a new "TaskScheduler" subclass that works 
basically the same way, but using a different implementation of 
"SingleStep()" (which "BasicTaskScheduler0" uses to implement 
"doEventLoop()").  I.e.,

     TaskScheduler (abstract)
         BasicTaskScheduler0 (abstract; defines "doEventLoop()", using 
"SingleStep()")
             BasicTaskScheduler (concrete; defines "SingleStep()")

We had a customer that wanted to implement "SingleStep()" slightly 
differently, and the best way to do this was to have him define a new 
subclass of "BasicTaskScheduler0" to do this.


	Ross Finlayson
	LIVE.COM
	<http://www.live.com/>