My Gardening Journey 2

Destructor or Finalize --- Whats the confusion??

C# really doesn't have a "true" destructor. The syntax resembles a C++ destructor, but it really is a finalizer. You wrote it correctly in the first part of your example:

~ClassName() { }

The above is syntactic sugar for a Finalize function. It ensures that the finalizers in the base are guaranteed to run, but is otherwise identical to overriding the Finalize function. This means that when you write the destructor syntax, you're really writing the finalizer.

According to Microsoft, the finalizer refers to the function that the garbage collector calls when it collects ("Finalize"), while the destructor is your bit of code that executes as a result (the syntactic sugar that becomes "Finalize"). They are so close to being the same thing that Microsoft should have never made the distinction.

Microsoft's use of the C++'s "destructor" term is misleading, because in C++ it is executed on the same thread as soon as the object is deleted or popped off the stack, while in C# it is executed on a separate thread at another time.

There is nothing like destructor in C#. It cannot, because you cannot decide when an object is destroyed, but the garbage collector (GC) does it. If object is beeing definitely deleted from managed memory, its finalizer method is called. Finalizers are created with the same syntax as desctructors (~ClassName(){...}), that is why you could miss it.

In finalizer, you cannot call any other managed object, because it is not determined if the other object still exists are was already deleted from memory. You can only free unmanaged resources, which are not under governance of the GC.

Recommended way how to work with resources is to use Dispose pattern. You implement IDisposable interface and in Dispose method, you can feel free to dispose all resource or whatever you use. Dispose method is never called by GC, so have full control on references (you can believe, that all objects you are referencing still exists). Good practice is also to call Dispose method (but in the way which prevent it from using managed resources) from finalizers to be sure that all resources are freed. Disposable patern is supported by keyword using, which ensures that Dispose is called.

If you free all resources in Dispose method, you can as well call GC.SupressFinalize(this). This instruct GC not to call finalizer on that object, because nothing more could be done.

(Thanks http://forums.codeguru.com/showthread.php?375773-difference-between-Finalize-and-destructor... and http://stackoverflow.com/questions/1076965/in-c-sharp-what-is-the-difference-between-a-destructor-and-a-finalize-method-in) for explanation .

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What is the use of Monitor in C#?

It provides a mechanism that synchronizes access to objects.

The Monitor class controls access to objects by granting a lock for an object to a single thread. Object locks provide the ability to restrict access to a block of code, commonly called a critical section. While a thread owns the lock for an object, no other thread can acquire that lock. You can also use Monitor to ensure that no other thread is allowed to access a section of application code being executed by the lock owner, unless the other thread is executing the code using a different locked object.

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What is static constructor?

Static constructor is used to initialize static data members as soon as the class is referenced first time, whereas an instance constructor is used to create an instance of that class with keyword. A static constructor does not take access modifiers or have parameters and can't access any non-static data member of a class.
Static constructors have the following properties:

    A static constructor does not take access modifiers or have parameters.

    A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.

    A static constructor cannot be called directly.

    The user has no control on when the static constructor is executed in the program.

    A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.

    Static constructors are also useful when creating wrapper classes for unmanaged code, when the constructor can call the LoadLibrary method.

    If a static constructor throws an exception, the runtime will not invoke it a second time, and the type will remain uninitialized for the lifetime of the application domain in which your program is running.
C# supports two types of constructor, a class constructor (static constructor) and an instance constructor (non-static constructor).

Static constructor is used to initialize static data members as soon as the class is referenced first time, whereas an instance constructor is used to create an instance of that class with <new> keyword. A static constructor does not take access modifiers or have parameters and can't access any non-static data member of a class.

Since static constructor is a class constructor, they are guaranteed to be called as soon as we refer to that class or by creating an instance of that class.

You may say, why not initialize static data members where we declare them in the code. Like this :

private static int id = 10;
private static string name = "jack";

Static data members can certainly be initialized at the time of their declaration but there are times when value of one static member may depend upon the value of another static member. In such cases we definitely need some mechanism to handle conditional initialization of static members. To handlesuch situation, C# provides static constructor.

Let me explain you with examples :

//File Name : Test.cs
using System;
namespace Constructor
{
class Test
{
//Declaration and initialization of static data member
private static int id = 5;
public static int Id
{
get
{
return id;
}
}
public static void print()
{
Console.WriteLine("Test.id = " + id);
}
static void Main(string[] args)
{
//Print the value of id
Test.print();
}
}
}

In the above example, static data member <id> is declared and initialized in same line. So if you compile and run this program your output would look similar to this :

Test.id = 5

Lets create one more class similar to class Test but this time the value of its static data member would depend on the value of static data member <id> of class Test.id.

//File Name : Test1.cs
using System;
namespace Constructor
{
class Test1
{
private static int id ;
//Static constructor, value of data member id is set conditionally here.
//This type of initialization is not possible at the time of declaration.
static Test1()
{
if( Test.Id < 10 )
{
id = 20;
}
else
{
id = 100;
}
Console.WriteLine("Static<Class> Constructor for Class Test1 Called..");
}
public static void print()
{
Console.WriteLine("Test1.id = " + id);
}
static void Main(string[] args)
{
//Print the value of id
Test1.print();
}
}
}

As you can see in the above static constructor, static data member <id> is initialized conditionally. This type of initialization is not possible at the time of declaration. This is where static constructor comes in picture. So if you compile and run this program your output would look similar to this :

Static<Class> Constructor for Class Test1 Called..
id = 20

Since <id> in class Test was initialized with a value of 5, therefore <id> in class Test1 got initialized to a value of 20.

Some important point regarding static constructor from C# Language Specification and C# Programmer's Reference :

1) The static constructor for a class executes before any instance of the class is created.
2) The static constructor for a class executes before any of the static members for the class are referenced.
3) The static constructor for a class executes after the static field initializers (if any) for the class.
4) The static constructor for a class executes at most one time during a single program instantiation
5) A static constructor does not take access modifiers or have parameters.
6) A static constructor is called automatically to initialize the class before the first instance is created or any static members are referenced.
7) A static constructor cannot be called directly.
8) The user has no control on when the static constructor is executed in the program.
9) A typical use of static constructors is when the class is using a log file and the constructor is used to write entries to this file.

Hopefully, this would clear the confusion some of developers have about static constructor.

Disclaimer: The above program is intended solely for learning purpose. Author will not be held responsible for any failure or damages caused due to any other usage.