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NS2 Object Construction

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    • 1. NS2: Shadow ObjectNS2: Shadow Object ConstructionConstruction by Teerawat Issariyakul http://www.ns2ultimate.com October 2010 http://www.ns2ultimate.com 1
    • 2. OutlineOutline Introduction Creating an OTcl object Shadow Object Construction Process Summary http://www.ns2ultimate.com 2
    • 3. IntroductionIntroduction This is a series on how NS2 binds C++ and OTcl together.This is the second topic of the series: 1.WhyTwo Languages? 2. Binding C++ and OTcl classes 3. Variable binding 4. OTcl command: Invoking C++ statements from the OTcl domain 5. Eval and result: Invoking OTcl statements from the C++ domain 6. Object binding and object construction process. http://www.ns2ultimate.com 3
    • 4. MotivationMotivation http://www.ns2ultimate.com 4  NS2 consists of 2 languages: ◦ OTcl: A user interface language used to create objects ◦ C++: A language defining the created objects’ attributes and behaviors  Objects in NS2 ◦ A user creates an object from the OTcl domain ◦ NS2 automatically creates a “shadow” object in the C++ domain  From the user perspective, these two objects are the same.
    • 5. Suppose we have two bound classes We are going to learn how EXACTLY NS2 auto. create a shadow object. What We Would Like to Do?What We Would Like to Do? http://www.ns2ultimate.com 5 TCPAgent C++ Agent/TCP OTcl bound user obj create c_obj Auto. construction by NS2 shadow object
    • 6. OutlineOutline Introduction Creating an OTcl object Shadow Object Construction Process Summary http://www.ns2ultimate.com 6
    • 7. Creating an OTcl ObjectCreating an OTcl Object http://www.ns2ultimate.com 7  An OTcl is created using the following syntax <className> create <var> [<args>] ◦ Create an object of class <className> ◦ Store the created object in the variable <var> ◦ <args>]is optional input argument for object construction.  There are two key steps when invoking new ◦ Executing instproc “alloc” to allocate memory to hold the object ◦ Executing instproc “init” (i.e., the constructor) to initialize class variables
    • 8. Instproc “Instproc “initinit”” http://www.ns2ultimate.com 8 It initializes class variables It is referred to as “the constructor” OOP structure ◦ Call the constructor of the base class first ◦ Use the instproc next
    • 9. Instproc “Instproc “nextnext”” http://www.ns2ultimate.com 9 Instproc “next” executes the instproc with the same name located in the parent class. Example ◦ Class Agent/TCP derives from class Agent ◦ When we see ◦ the statement “eval $self next” executes “Agent init {}”. Agent/TCP instproc init {} { eval $self next … }
    • 10. OutlineOutline Introduction Creating an OTcl object Shadow Object Construction Process Summary http://www.ns2ultimate.com 10
    • 11. Shadow Object ConstructionShadow Object Construction The process consists of two part ◦ Part I: OTcl—Creating an object using “new” ◦ Part II: C++—Shadow object construction http://www.ns2ultimate.com 11 Part I: OTcl Part II: C++
    • 12. Shadow Object ConstructionShadow Object Construction Let’s use the following example ◦ OTcl class: Agent/TCP ◦ C++ class: TcpAgent In OTcl, create an object using new Agent/TCP In C++, create a shadow TcpAgent object http://www.ns2ultimate.com 12
    • 13. Part I: OTclPart I: OTcl Main steps of Part I: The OTcl statement new <classname> [<args>] The OTcl statement $classname create $o $args The instproc alloc of the OTcl class <classname> The instproc init of the OTcl class <classname> The instproc init of the OTcl class SplitObject The OTcl statement $self create-shadow $args http://www.ns2ultimate.com 13
    • 14. Part I: OTclPart I: OTcl 1. The OTcl statement new <classname> [<args>]Execute a global procedure “new” http://www.ns2ultimate.com 14 proc new { className args } { set o [SplitObject getid] if [catch "$className create $o $args" msg] { ... } return $o } step 2
    • 15. Part I: OTclPart I: OTcl 2.The OTcl statement $classname create $o $args Again, the instproc create invokes two instprocs in Steps 3 and 4. 3.The instproc alloc of the OTcl class <classname>: Memory allocation http://www.ns2ultimate.com 15
    • 16. Part I: OTclPart I: OTcl 4.The instproc init of the OTcl class <classname> A general structure of the the instproc init is to invoke the instproc init of the base class until reaching the top level class, e.g., The top level class is class SplitObject  Step 5 http://www.ns2ultimate.com 16 Agent/TCP instproc init {} { eval $self next … }
    • 17. Part I: OTclPart I: OTcl 5. The instproc init of the OTcl class SplitObject 6. The OTcl statement $self create-shadow $args:  This executes, for example, instproc create-shadow of class Agent/TCP http://www.ns2ultimate.com 17 SplitObject instproc init args { $self next if [catch "$self create-shadow $args"] { error "__FAILED_SHADOW_OBJECT_" "" } }
    • 18. Part II: C++Part II: C++ http://www.ns2ultimate.com 18 Part I completes with the OTcl command create-shadow. In Part II, we are moving to the C++ domain. Part I: OTcl Part II: C++
    • 19. Part II: C++Part II: C++ http://www.ns2ultimate.com 19 Let’s use an example of class TcpAgent Main steps of Part II: Step 6 in Part I The C++ function create-shadow(...) of class TclClass  The C++ function create(...) of class TcpClass The C++ statement new TcpAgent()
    • 20. Part II: C++Part II: C++ http://www.ns2ultimate.com 20 1. Step 6 in Part I: The OTcl command create-shadow is bound to The C++ function create-shadow(...) of class TclClass 2.The C++ function create-shadow(...) of class TclClass 3.The C++ function create(...) of class TcpClass
    • 21. Part II: C++Part II: C++ http://www.ns2ultimate.com 21 3.The C++ function create(...) of class TcpClass 4. The C++ statement new TcpAgent(): Create a shadow object static class TcpClass : public TclClass { public: TcpClass() : TclClass("Agent/TCP") {} TclObject* create(int , const char*const*) { return (new TcpAgent()); } } class_tcp; Step 4
    • 22. OutlineOutline Introduction Creating an OTcl object Shadow Object Construction Process Summary http://www.ns2ultimate.com 22
    • 23. SummarySummary In NS2, a user creates an object from the OTcl domain using a global procedure “new” NS2 automatically creates a so-called shadow object in the C++ domain. The shadow object construction consists of 2 parts: ◦ Part 1: Execute OTcl constructors ◦ Part II: Create a shadow object in the C++ domain. http://www.ns2ultimate.com 23
    • 24. For more information aboutFor more information about NS 2NS 2 Please see this book from Springer T. Issaraiyakul and E. Hossain, “Introduction to Network Simulator NS2”, Springer 2009 http://www.ns2ultimate.com 24