CCR.... Paper 1

Alsalam alikom wa ra7mat Allah wa barakatoh

It's so long since we've posted anything here...

Today we will speak a little about CCR... "Microsoft's light weight concurrency
library"

What is CCR?

It's the abbreviation for Concurrency and Coordination Runtime.. which is a library
that Microsoft recently released with Microsoft
Robotics Studio library..

CCR solves a lot of troubles we usually face when coding using Threads (and we will
see shortly how)..

Consider this sample (non-real) code:

void OnOkay(Okay state)
{
// Dothings
}

void OnCancel(Cancel state)
{
// Do Other things
}

and considering that you want to work asynchronously, that's you want to wait for a message (Okay or Cancel), know it's type and then call the aproperciate method for it, then wait for another message... etc, something like this:

void ReadMessages()
{
while (true)
{
Message message = PullMessage(DispatchQueue);
switch(typeof(message))
{
case Okay:
OnOkay(message as Okay);
...
}
}

Just that simple...
BUT, now your method waits till the handler finishes before polling the next message...
What to do ?
We can make a thread to run the handler in.. so, instead of doing this:
case Okay:
OnOkay(message as Okay);

we will replace it with
case Okay:
Thread thread = new Thread(new ThreadStart(delegate(){
OnOkay(message as Okay);
}));
thread.Start();

Again, just simple..
Now, what if I told you that the DispatcherQueue is accessed from so many threads,
What to do?
Okay, simple, put a lock statement to prevent multiple threads from accessing the
Queue at the same time..

Simple...
Now, What if it's just like this:
port.Post(new Okay());
and
port.Post(new Cancel());

and it's thread safe, controls the number of threads open, just that neat.
Isn't that better?

CCR doesn't offer a new technology, it's just an elegant way to manage you thread
pools and conccurent tasks.

A few definitions:

• Dispatcher Class:
  It's basically a ThreadPool.. which we can consider like a List of threads.. but it has a predefined number of threads (that can be passed in the constructor)
  Dispatcher Dispatcher = new Dispatcher(5);
  


• DispatcherQueue Class:
  It's a queue of delegates each holds a handler that's waiting for certain type of messages.
  
  
• Port:
  Something that you send/receive through... it's a virtual port (think about it like your printer/scanner port)
  
  
• Arbiter:
  A static class that manges adding/removing your methods (wrapped in delegate objects)

So, enough speaking about how nice CCR is...
Wait the next paper to give some sample code and explanation...

Till then, you can check a good resource: MSDN.. About CCR

Stay in touch...

Alsalam alikom wa ra7mat Allah wa barakatoh