基于reSIProcate的SIP协议栈研究--DUM和SIPStack的多线程运行

> In the latest work session we've done some refactoring of resiprocate
> to support having multiple Transaction Users (TU) in a resip-based
> application. There are a few implications and interface changes.
> 
> - DialogUsageManager constructor now must take a SipStack&
> - UserProfile::setDigestCredential no longer takes an aor argument
> since the UserProfile is already bound to an aor
> - Applications can have multiple TransactionUsers (e.g.
> DialogUsageManager or Proxy). Each TU needs to register with the
> TransactionUserSelector using this interface
> SipStack::registerTransactionUser(TransactionUser& tu). The
> DialogUsageManager will do this for you in its constructor.
> 
> Keep in mind that this means your application needs to make a SipStack
> and pass it into the DialogUsageManager. If you are creating multiple
> TUs you should share the same SipStack with each of these.
> 
> Each incoming message is  matched against the list of TUs that have
> been registered with the SipStack.  More to follow on this topic.

//DialogUsageManager 和 SipStack 运行在各自独立线程，和程序主线程独立
> As a convenience, there are two classes which help you run your
> DialogUsageManager and/or SipStack in their own threads. For example,
> if you were writing a presence server or registrar, you could use the
> following approach:

SipStack stack;
StackThread stackThread(stack);
DialogUsageManager dum(stack);
DumThread dumThread(dum);
 
stackThread.run();
dumThread.run();
stackThread.join();
dumThread.join();


//DialogUsageManager和程序主线程一起，SipStack运行于独立的线程
> If you are implementing a useragent such as a softphone that might
> have a gui component running the same thread as the dum, use this
> approach instead:

SipStack stack;
 StackThread stackThread(stack);
 
 DialogUsageManager dum(stack);
 stackThread.run();
 
 while (!shutdown) // some local variable

 {
     while (dum.process());
     // do your gui stuff here.

 }
 stackThread.join();



//DialogUsageManager和SipStack都运行在程序主线程同一线程中
> You can also run without a StackThread if you'd like everything to run
> in a single thread.

SipStack stack;
 DialogUsageManager dum(stack);
 while (!shutdown) // some local variable

 {
       try
       {
          resip::FdSet fdset;
          buildFdSet(fdset);
          stack.buildFdSet(fdset);
          int ret = fdset.selectMilliSeconds(stack.getTimeTillNextProcessMS());
          if (ret >= 0)
          {
             stack.process(fdset);
          }
       }
       catch (BaseException& e)
       {
          InfoLog (<< "Unhandled exception: " << e);
       }
 
     while (dum.process());
     // do your gui stuff here.

 }



> There will be more to follow on how to use the new Proxy TU - as well

> as how to use the Proxy TU in conjunction with one or more User Agent
> TUs.


Here is the explaination of some lines of code above:

buildFdSet - iterates through all of the stacks socket read/write handles
and builds a list to pass to the select function.

selectMilliSeconds - Waits for one of the handles returned from buildFdSet
to be signaled (ie. inbound SIP message) - waits for a specified number of
milliseconds.

getTimeTillNextProcessMs() - iterates through all timers to see when the
next time that the stack will need to do work to service timers

process - iterates through all transports FIFOs and timers and processes
inbound and/or SIP messages and timer expirations.  ie.  Does all of the
work!