NS2 Object Construction

NS2: Shadow ObjectNS2: Shadow Object
ConstructionConstruction
by Teerawat Issariyakul
http://www.ns2ultimate.com
October 2010
http://www.ns2ultimate.com 1

OutlineOutline
Introduction
Creating an OTcl object
Shadow Object Construction Process
Summary

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.

MotivationMotivation
 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.

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?
TCPAgent
C++
Agent/TCP
OTcl
bound
user
obj
create
c_obj
Auto. construction by NS2
shadow object

OutlineOutline
Introduction
Summary

Creating an OTcl ObjectCreating an OTcl Object
 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

Instproc “Instproc “initinit””
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

Instproc “Instproc “nextnext””
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
…
}

OutlineOutline
Introduction
Summary

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
Part I: OTcl Part II: C++

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

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

1. The OTcl statement new <classname>
[<args>]Execute a global procedure
“new”
proc new { className args } {
set o [SplitObject getid]
if [catch "$className create $o $args" msg] {
...
}
return $o
}
step 2

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

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
Agent/TCP instproc init
{} {
eval $self next
…
}

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
SplitObject instproc init args {
$self next
if [catch "$self create-shadow $args"] {
error "__FAILED_SHADOW_OBJECT_" ""
}
}

Part II: C++Part II: C++
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++

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()

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

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

OutlineOutline
Introduction
Summary

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.

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

NS2 Object Construction

More Related Content

What's hot

Viewers also liked

Similar to NS2 Object Construction

Recently uploaded

NS2 Object Construction

Editor's Notes