Consider the following ECMAScript:

var mather=new ActiveXObject("Arithmetic.Math")

WScript.Echo(mather.Sum(5,5))

WScript.Echo(mather.Sum(5,5))

Output is: 10 twice. No brainer.

Arithmetic.Math could be an in-process (loaded in the same process of COM Client), local (loaded in different process on the same computer) or remote (loaded in a process on different computer) COM Server. The above COM Client is unaware of this fact.

By now, Arithmetic.Math code could be the following .NET class properly registered with regasm.exe:

public class Arithmetic.Math

{

public int Sum(int a, int b)

{

return a + b;

}

}

Now, we want a method to sum accumulatively and return each time the total so far:

var mather=new ActiveXObject("Arithmetic.Math")

WScript.Echo(mather.Memorysum(5))

WScript.Echo(mather.Memorysum(5))

Output is:

5

10

Suppose Arithmetic.Math is now the following ServicedComponent-derived class regsvcs.exe-registered within a COM+ Application activated as a Server and as a NT Service:

public class Arithmetic.Math : System.EnterpriseServices.ServicedComponent

{

private int m;public Math()

{

m = 0;

}public int Sum(int a, int b)

{

return a + b;

}public int Memorysum(int n)

{

m += n;

return m;

}

}

What happen when our client script is launched concurrently different times and Memorysum method is invoked simultaneously? What output get each?

Answer is: each client gets the same output:

5

10

Why? Because of the COM+ object per client model, each client get its own Arithmetic.Math object.

Now suppose we want a method that sums accumulatively across different clients:

public class Arithmetic.Math : System.EnterpriseServices.ServicedComponent

{

private int m;

private static int globalm;

private static volatile object syncroot = new object();public Math()

{

m = 0;

}public int Sum(int a, int b)

{

return a + b;

}public int Memorysum(int n)

{

m += n;

return m;

}public int Globalsum(int n)

{

lock (syncroot)

{

globalm += n;

}

return globalm;

}

}

What happen now when our client script is modified as below and launched concurrently different times and Globalsum method is invoked simultaneously? What output get each?

var mather=new ActiveXObject("Arithmetic.Math")

WScript.Echo(mather.Globalsum(5))

WScript.Echo(mather.Globalsum(5))

Each output will be different now as each Arithmetic.Math object share the same state and are in the same AppDomain.

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