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Difference between finalizer and finally in C# [duplicate]

I am studying how garbage collector works in c#. I am confused over the use of Destructor, Dispose and Finalize methods.
As per my research and understandings, having a Destructor method within my class will tell the garbage collector to perform the garbage collection in the way mentioned in the destructor method which cannot be called explicitly on the instances of the class.
The Dispose method is meant to provide the user to control the garbage collection. The Finalize method frees the resources used by the class, but not the object itself.
I am not sure if I understand it the right way. Please clarify the doubts. Any further links or guides are welcome.

Destructor implicitly calls the Finalize method, they are technically the same. Dispose is available with objects that implement the IDisposable interface.
You may see : Destructors C# - MSDN
The destructor implicitly calls Finalize on the base class of the
object.
Example from the same link:
class Car
{
~Car() // destructor
{
// cleanup statements...
}
}
The Destructor's code is implicitly translated to the following code:
protected override void Finalize()
{
try
{
// Cleanup statements...
}
finally
{
base.Finalize();
}
}
Your understanding for the Destructor is right:
From MSDN
The programmer has no control over when the destructor is called
because this is determined by the garbage collector. The garbage
collector checks for objects that are no longer being used by the
application. If it considers an object eligible for destruction, it
calls the destructor (if any) and reclaims the memory used to store
the object. Destructors are also called when the program exits. It is
possible to force garbage collection by calling Collect, but most of
the time, this should be avoided because it may create performance
issues.

In C# terms, a destructor and finalizer are basically interchangeable concepts, and should be used to release unmanaged resources when a type is collected, for example external handles. It is very rare that you need to write a finalizer.
The problem with that is that GC is non-deterministic, so the Dispose() method (via IDisposable) makes it possible to support deterministic cleanup. This is unrelated to garbage collection, and allows the caller to release any resources sooner. It is also suitable for use with managed resources (in addition to unmanaged), for example if you have a type that encapsulates (say) a database connection, you might want disposing of the type to release the connection too.

Why does the traditional Dispose pattern suppress finalize?

Assuming this as the traditional Dispose pattern (taken from devx but seen on many websites)
class Test : IDisposable
{
private bool isDisposed = false;
~Test()
{
Dispose(false);
}
protected void Dispose(bool disposing)
{
if (disposing)
{
// Code to dispose the managed resources of the class
}
// Code to dispose the un-managed resources of the class
isDisposed = true;
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
I don't understand why we call GC.SupressFinalize(this). This requires me to write my own managed resource disposal, including nulling my references? I'm a bit lost, I must admit. Could someone shed some light on this pattern?
Ideally, I would like to only dispose my unmanaged resources and let the GC do the managed collecting by itself.
Actually, I don't even know why we specify a finalizer. In any case, the coder should call dispose himself, now shouldn't he? If that's just a fallback mechanism, I'd remove it.

The IDisposable pattern is used so that the object can clean up its resources deterministically, at the point when the Dispose method is called by the client code.
The finaliser is only there as a fallback in case the client code fails to call Dispose for some reason.
If the client code calls Dispose then the clean-up of resources is performed there-and-then and doesn't need to be done again during finalisation. Calling SuppressFinalize in this situation means that the object no longer incurs the extra GC cost of finalisation.
And, if your own class only uses managed resources then a finaliser is completely unnecessary: The GC will take care of any managed resources, let those resources themselves worry about whether they need a fallback finaliser. You should only consider a finaliser in your own class if it directly handles unmanaged resources.

SuppressFinalize only suppresses any custom finalizer.
It does not alter any other GC behavior.
You never need to explicitly null out references. (Unless you want them to be collected early)
There is no difference between a class without any finalizer and an instance on which you've called SuppressFinalize.
Calling SuppressFinalize prevents an extra call to Dispose(false), and makes the GC somewhat faster. (finalizers are expensive)
Note that classes without unmanaged resources should not have a finalizer. (They should still call SuppressFinalize, unless they're sealed; this allows inherited classes to add unmanaged resources)

The SuppressFinalize call exists in case some derived class decides to add a finalizer. If a normal dispose completes successfully, finalization won't be necessary; even if a derived class decides to add one, the SuppressFinalize call will prevent it from executing and interfering with garbage collection.
To understand why this is important, you should think of finalization not as being part of garbage collection, but rather something that happens before it. When a class registers for finalization (automatic on creation, if it overrides Finalize) it is put into a special list called the Finalization Queue. No object in the Finalization Queue, nor any object referenced directly or indirectly by an object in the queue, can be garbage-collected, but if any object in the finalization queue is found to have no rooted references other than from the queue, the object will be pulled from the queue and the finalizer will run. While the finalizer is being dispatched, the object will not be collectable (since a reference will exist during the dispatch); once the finalizer is complete, there will usually not be any references to the object anymore, so it (and objects referenced thereby) will usually be collectable.
Personally, I think the SuppressFinalize is silly, since I can think of no good reason why a derived class should ever have a finalizer. If a derived class is going to add souse unmanaged resources(*) which the parent class will know nothing about, another class should be created for the purpose of holding those resources; the parent class should hold a reference to that. That way, the parent class itself will not need finalization, and objects which are referenced by the parent class won't be needlessly blocked from garbage collection.

From Msdn :
"
This method sets a bit in the object header, which the system checks when calling finalizers. The obj parameter is required to be the caller of this method.
Objects that implement the IDisposable interface can call this method from the IDisposable.Dispose method to prevent the garbage collector from calling Object.Finalize on an object that does not require it.
"
So it prevents an extra call from the GC. If it is called from within the the finalizer method, when object is being finalized, then it wont do anything, as it is already being finalised.
Otherwise, the GC is allowed to reclaim memory, without finalisation of the object, thus making things faster.

As noted on MSDN executing the Finalize method is costly. By calling dispose you've already self finalized your class so the finalizer doesn't need to be called. The finalizer is implemented in case the Dispose is never called directly by your code (or whoever 'owns' the instance).

// If the monitor.Dispose method is not called, the example displays the following output:
// ConsoleMonitor instance....
// The ConsoleMonitor class constructor.
// The Write method.
// The ConsoleMonitor finalizer.
// The Dispose(False) method.
// Disposing of unmanaged resources.
//
// If the monitor.Dispose method is called, the example displays the following output:
// ConsoleMonitor instance....
// The ConsoleMonitor class constructor.
// The Write method.
// The Dispose method.
// The Dispose(True) method.
// Disposing of managed resources.
// Disposing of unmanaged resources.
From https://msdn.microsoft.com/en-us/library/system.gc.suppressfinalize(v=vs.110).aspx

Why should we call SuppressFinalize when we don't have a destructor

I have few Question for which I am not able to get a proper answer .
1) Why should we call SuppressFinalize in the Dispose function when we don't have a destructor .
2) Dispose and finalize are used for freeing resources before the object is garbage collected. Whether it is managed or unmanaged resource we need to free it , then why we need a condition inside the dispose function , saying pass 'true' when we call this overridden function from IDisposable:Dispose and pass false when called from a finalize.
See the below code I copied from net.
class Test : IDisposable
{
private bool isDisposed = false;
~Test()
{
Dispose(false);
}
protected void Dispose(bool disposing)
{
if (disposing)
{
// Code to dispose the managed resources of the class
}
// Code to dispose the un-managed resources of the class
isDisposed = true;
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
what if I remove the boolean protected Dispose function and implement the as below.
class Test : IDisposable
{
private bool isDisposed = false;
~Test()
{
Dispose();
}
public void Dispose()
{
// Code to dispose the managed resources of the class
// Code to dispose the un-managed resources of the class
isDisposed = true;
// Call this since we have a destructor . what if , if we don't have one
GC.SuppressFinalize(this);
}
}

I'm going out on a limb here, but... most people don't need the full-blown dispose pattern. It's designed to be solid in the face of having direct access to unmanaged resources (usually via IntPtr) and in the face of inheritance. Most of the time, neither of these is actually required.
If you're just holding a reference to something else which implements IDisposable, you almost certainly don't need a finalizer - whatever holds the resource directly is responsible for dealing with that. You can make do with something like this:
public sealed class Foo : IDisposable
{
private bool disposed;
private FileStream stream;
// Other code
public void Dispose()
{
if (disposed)
{
return;
}
stream.Dispose();
disposed = true;
}
}
Note that this isn't thread-safe, but that probably won't be a problem.
By not having to worry about the possibility of subclasses holding resources directly, you don't need to suppress the finalizer (because there isn't one) - and you don't need to provide a way of subclasses customising the disposal either. Life is simpler without inheritance.
If you do need to allow uncontrolled inheritance (i.e. you're not willing to bet that subclasses will have very particular needs) then you need to go for the full pattern.
Note that with SafeHandle from .NET 2.0, it's even rarer that you need your own finalizer than it was in .NET 1.1.
To address your point about why there's a disposing flag in the first place: if you're running within a finalizer, other objects you refer to may already have been finalized. You should let them clean up themselves, and you should only clean up the resources you directly own.

Here are the main facts
1) Object.Finalize is what your class overrides when it has a Finalizer. the ~TypeName() destructor method is just shorthand for 'override Finalize()' etc
2) You call GC.SuppressFinalize if you are disposing of resources in your Dispose method before finalization (i.e. when coming out of a using block etc). If you do not have a Finalizer, then you do not need to do this. If you have a Finalizer, this ensures that the object is taken off of the Finalization queue (so we dont dispose of stuff twice as the Finalizer usually calls the Dispose method as well)
3) You implement a Finalizer as a 'fail safe' mechanism. Finalizers are guaranteed to run (as long as the CLR isnt aborted), so they allow you to make sure code gets cleaned up in the event that the Dispose method was not called (maybe the programmer forgot to create the instance within a 'using' block etc.
4) Finalizers are expensive as Types that have finalizers cant be garbage collected in a Generation-0 collection (the most efficient), and are promoted to Generation-1 with a reference to them on the F-Reachable queue, so that they represent a GC root. it's not until the GC performs a Generation-1 collection that the finalizer gets called, and the resources are released - so implement finalizers only when very important - and make sure that objects that require Finalization are as small as possible - because all objects that can be reached by your finalizable object will be promoted to Generation-1 also.

Keep the first version, it is safer and is the correct implementation of the dispose pattern.
Calling SuppressFinalize tells the GC that you have done all the destruction/disposing yourself (of resources held by your class) and that it does not need to call the destructor.
You need the test in case the code using your class has already called dispose and you shouldn't tell the GC to dispose again.
See this MSDN document (Dispose methods should call SuppressFinalize).

1. Answer for the first question
Basically, you don't have to call SuppressFinalize method if your class doesn't have a finalize method (Destructor). I believe people call SupressFinalize even when there is no finalize method because of lack of knowledge.
2. Answer for the second question
Purpose of the Finalize method is to free un-managed resources. The most important thing to understand is that, Finalize method is called when the object is in the finalization queue. Garbage collector collects all the objects that can be destroy. Garbage Collector adds objects those have got finalization to the finalization queue before destroy. There is another .net background process to call the finalize method for the objects those are in the finalization queue. By the time that background process execute the finalize method, that particular object's other managed reference may have been destroyed. Because there is no specific order when it comes to the finalization execution. So, the Dispose Pattern wants to make sure that finalize method do not try to access managed objects. That's why managed objects are going in side "if (disposing)" clause which is unreachable for the finalize method.

You should always call SuppressFinalize() because you might have (or have in the future) a derived class that implements a Finalizer - in which case you need it.
Let's say you have a base class that doesn't have a Finalizer - and you decided not to call SuppressFinalize(). Then 3 months later you add a derived class that adds a Finalizer. It is likely that you will forget to go up to the base class and add a call to SuppressFinalize(). There is no harm in calling it if there is no finalizer.
My suggested IDisposable pattern is posted here: How to properly implement the Dispose Pattern

When would dispose method not get called?

I was reading this article the other day and was wondering why there was a Finalizer along with the Dispose method. I read here on SO as to why you might want to add Dispose to the Finalizer. My curiousity is, when would the Finalizer be called over the Dispose method itself? Is there a code example or is it based on something happening on the system the software is running? If so, what could happen to not have the Dispose method run by the GC.

The purpose of the finaliser here is simply a safety precaution against memory leaks (if you happen not to call Dispose explicitly). It also means you don't have to dispose your objects if you want them to release resources when the program shutdowns, since the GC will be forced to finalise and collect all objects anyway.
As a related point, it is important to dispose the object slightly differently when doing so from the finaliser.
~MyClass()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected void Dispose(disposing)
{
if (!this.disposed)
{
if (disposing)
{
// Dispose managed resources here.
}
// Dispose unmanaged resources here.
}
this.disposed = true;
}
The reason you do not want to dispose managed resources in your finaliser is that you would actually be creating strong references to them in doing so, and this could prevent the GC from doing it's job properly and collecting them. Unmanaged resources (e.g. Win32 handles and such) should always be explicitly closed/disposed, of course, since the CLR has no knowledge of them.

This is mostly there to protect yourself. You cannot dictate what the end user of your class will do. By providing a finalizer in addition to a Dispose method, the GC will "Dispose" of your object, freeing your resources appropriately, even if the user forgets to call Dispose() or mis-uses your class.

The Finalizer is called when the object is garbage collected. Dispose needs to be explicitly called. In the following code the finalizer will be called but the Dispose method is not.
class Foo : IDisposable
{
public void Dispose()
{
Console.WriteLine("Disposed");
}
~Foo()
{
Console.WriteLine("Finalized");
}
}
...
public void Go()
{
Foo foo = new Foo();
}

The dispose method must be explicitly called, either by calling Dispose() or by having the object in a using statement. The GC will always call the finalizer, so if there is something that needs to happen before the objects are disposed of the finalizer should at least check to make sure that everything in the object is cleaned up.
You want to avoid cleaning up objects in the finalizer if at all possible, because it causes extra work compared to disposing them before hand (like calling dispose), but you should always at least check in the finalizer if there are objects lying around that need to be removed.

An important but subtle note not yet mentioned: a seldom-considered purpose of Dispose is to prevent an object from being cleaned up prematurely. Objects with finalizers must be written carefully, lest a finalizer run earlier than expected. A finalizer can't run before the start of the last method call that will be made on an object(*), but it might sometimes run during the last method call if the object will be abandoned once the method completes. Code which properly Dispose an object can't abandon the object before calling Dispose, so there's no danger of a finalizer wreaking havoc on code which properly uses Dispose. On the other hand, if the last method to use an object makes use of entities which will be cleaned up in the finalizer after its last use of the object reference itself, it's possible for the garbage-collector to call Finalize on the object and clean up entities that are still in use. The remedy is to ensure any call method which uses entities that are going to get cleaned up by a finalizer must be followed at some point by a method call which makes use of "this". GC.KeepAlive(this) is a good method to use for that.
(*) Non-virtual methods which are expanded to in-line code that doesn't do anything with the object may be exempt from this rule, but Dispose usually is, or invokes, a virtual method.

Finalize vs Dispose

Why do some people use the Finalize method over the Dispose method?
In what situations would you use the Finalize method over the Dispose method and vice versa?

The finalizer method is called when your object is garbage collected and you have no guarantee when this will happen (you can force it, but it will hurt performance).
The Dispose method on the other hand is meant to be called by the code that created your class so that you can clean up and release any resources you have acquired (unmanaged data, database connections, file handles, etc) the moment the code is done with your object.
The standard practice is to implement IDisposable and Dispose so that you can use your object in a using statment. Such as using(var foo = new MyObject()) { }. And in your finalizer, you call Dispose, just in case the calling code forgot to dispose of you.

Others have already covered the difference between Dispose and Finalize (btw the Finalize method is still called a destructor in the language specification), so I'll just add a little about the scenarios where the Finalize method comes in handy.
Some types encapsulate disposable resources in a manner where it is easy to use and dispose of them in a single action. The general usage is often like this: open, read or write, close (Dispose). It fits very well with the using construct.
Others are a bit more difficult. WaitEventHandles for instances are not used like this as they are used to signal from one thread to another. The question then becomes who should call Dispose on these? As a safeguard types like these implement a Finalize method, which makes sure resources are disposed when the instance is no longer referenced by the application.

Finalize is the backstop method, called by the garbage collector when it reclaims an object. Dispose is the "deterministic cleanup" method, called by applications to release valuable native resources (window handles, database connections, etc.) when they are no longer needed, rather than leaving them held indefinitely until the GC gets round to the object.
As the user of an object, you always use Dispose. Finalize is for the GC.
As the implementer of a class, if you hold managed resources that ought to be disposed, you implement Dispose. If you hold native resources, you implement both Dispose and Finalize, and both call a common method that releases the native resources. These idioms are typically combined through a private Dispose(bool disposing) method, which Dispose calls with true, and Finalize calls with false. This method always frees native resources, then checks the disposing parameter, and if it is true it disposes managed resources and calls GC.SuppressFinalize.

Finalize gets called by the GC when this object is no longer in use.
Dispose is just a normal method which the user of this class can call to release any resources.
If user forgot to call Dispose and if the class have Finalize implemented then GC will make sure it gets called.

Finalize
Finalizers should always be protected, not public or private so that the method cannot be called from the application's code directly and at the same time, it can make a call to the base.Finalize method
Finalizers should release unmanaged resources only.
The framework does not guarantee that a finalizer will execute at all on any given instance.
Never allocate memory in finalizers or call virtual methods from finalizers.
Avoid synchronization and raising unhandled exceptions in the finalizers.
The execution order of finalizers is non-deterministic—in other words, you can't rely on another object still being available within your finalizer.
Do not define finalizers on value types.
Don't create empty destructors. In other words, you should never explicitly define a destructor unless your class needs to clean up unmanaged resources and if you do define one, it should do some work. If, later, you no longer need to clean up unmanaged resources in the destructor, remove it altogether.
Dispose
Implement IDisposable on every type that has a finalizer
Ensure that an object is made unusable after making a call to the Dispose method. In other words, avoid using an object after the Dispose method has been called on it.
Call Dispose on all IDisposable types once you are done with them
Allow Dispose to be called multiple times without raising errors.
Suppress later calls to the finalizer from within the Dispose method using the GC.SuppressFinalize method
Avoid creating disposable value types
Avoid throwing exceptions from within Dispose methods
Dispose/Finalized Pattern
Microsoft recommends that you implement both Dispose and Finalize when working with unmanaged resources. The Finalize implementation would run and the resources would still be released when the object is garbage collected even if a developer neglected to call the Dispose method explicitly.
Cleanup the unmanaged resources in the Finalize method as well as Dispose method. Additionally call the Dispose method for any .NET objects that you have as components inside that class(having unmanaged resources as their member) from the Dispose method.

There're some keys about from the book MCSD Certification Toolkit (exam 70-483) pag 193:
destructor ≈(it's almost equal to) base.Finalize(), The destructor is converted into an override version of the Finalize method that executes the destructor’s code and then calls the base class’s Finalize method. Then its totally non deterministic you can't able to know when will be called because depends on GC.
If a class contains no managed resources and no unmanaged resources, it shouldn't implement IDisposable or have a destructor.
If the class has only managed resources, it should implement IDisposable but it shouldn't have a destructor. (When the destructor executes, you can’t be sure managed objects still
exist, so you can’t call their Dispose() methods anyway.)
If the class has only unmanaged resources, it needs to implement IDisposable and needs a destructor in case the program doesn’t call Dispose().
Dispose() method must be safe to run more than once. You can achieve that by using a variable to keep track of whether it has been run before.
Dispose() should free both managed and unmanaged resources.
The destructor should free only unmanaged resources. When the destructor executes, you
can’t be sure managed objects still exist, so you can’t call their Dispose methods anyway. This is obtained by using the canonical protected void Dispose(bool disposing) pattern, where only managed resources are freed (disposed) when disposing == true.
After freeing resources, Dispose() should call GC.SuppressFinalize, so the object can
skip the finalization queue.
An Example of a an implementation for a class with unmanaged and managed resources:
using System;
class DisposableClass : IDisposable
{
// A name to keep track of the object.
public string Name = "";
// Free managed and unmanaged resources.
public void Dispose()
{
FreeResources(true);
// We don't need the destructor because
// our resources are already freed.
GC.SuppressFinalize(this);
}
// Destructor to clean up unmanaged resources
// but not managed resources.
~DisposableClass()
{
FreeResources(false);
}
// Keep track if whether resources are already freed.
private bool ResourcesAreFreed = false;
// Free resources.
private void FreeResources(bool freeManagedResources)
{
Console.WriteLine(Name + ": FreeResources");
if (!ResourcesAreFreed)
{
// Dispose of managed resources if appropriate.
if (freeManagedResources)
{
// Dispose of managed resources here.
Console.WriteLine(Name + ": Dispose of managed resources");
}
// Dispose of unmanaged resources here.
Console.WriteLine(Name + ": Dispose of unmanaged resources");
// Remember that we have disposed of resources.
ResourcesAreFreed = true;
}
}
}

99% of the time, you should not have to worry about either. :) But, if your objects hold references to non-managed resources (window handles, file handles, for example), you need to provide a way for your managed object to release those resources. Finalize gives implicit control over releasing resources. It is called by the garbage collector. Dispose is a way to give explicit control over a release of resources and can be called directly.
There is much much more to learn about the subject of Garbage Collection, but that's a start.

The finalizer is for implicit cleanup - you should use this whenever a class manages resources that absolutely must be cleaned up as otherwise you would leak handles / memory etc...
Correctly implementing a finalizer is notoriously difficult and should be avoided wherever possible - the SafeHandle class (avaialble in .Net v2.0 and above) now means that you very rarely (if ever) need to implement a finalizer any more.
The IDisposable interface is for explicit cleanup and is much more commonly used - you should use this to allow users to explicitly release or cleanup resources whenever they have finished using an object.
Note that if you have a finalizer then you should also implement the IDisposable interface to allow users to explicitly release those resources sooner than they would be if the object was garbage collected.
See DG Update: Dispose, Finalization, and Resource Management for what I consider to be the best and most complete set of recommendations on finalizers and IDisposable.

Diff between Finalize and Dispose methods in C#.
GC calls the finalize method to reclaim the unmanaged resources(such as file operarion, windows api, network connection, database connection) but time is not fixed when GC would call it. It is called implicitly by GC it means we do not have low level control on it.
Dispose Method: We have low level control on it as we call it from the code. we can reclaim the unmanaged resources whenever we feel it is not usable.We can achieve this by implementing IDisposal pattern.

The summary is -
You write a finalizer for your class if it has reference to unmanaged
resources and you want to make sure that those unmanaged resources
are released when an instance of that class is garbage collected
automatically. Note that you can't call the Finalizer of an object explicitly - it's called automatically by the garbage collector as and when it deems necessary.
On the other hand, you implement the IDisposable interface(and
consequently define the Dispose() method as a result for your class) when your class
has reference to unmanaged resources, but you don't want to wait for
the garbage collector to kick in (which can be anytime - not in
control of the programmer) and want to release those resources as
soon as you are done. Thus, you can explicitly release unmanaged resources by calling an object's Dispose() method.
Also, another difference is - in the Dispose() implementation, you should release managed resources as well, whereas that should not be done in the Finalizer. This is because it's very likely that the managed resources referenced by the object have already been cleaned up before it's ready to be finalized.
For a class that uses unmanaged resources, the best practice is to define both - the Dispose() method and the Finalizer - to be used as a fallback in case a developer forgets to explicitly dispose off the object. Both can use a shared method to clean up managed and unmanaged resources :-
class ClassWithDisposeAndFinalize : IDisposable
{
// Used to determine if Dispose() has already been called, so that the finalizer
// knows if it needs to clean up unmanaged resources.
private bool disposed = false;
public void Dispose()
{
// Call our shared helper method.
// Specifying "true" signifies that the object user triggered the cleanup.
CleanUp(true);
// Now suppress finalization to make sure that the Finalize method
// doesn't attempt to clean up unmanaged resources.
GC.SuppressFinalize(this);
}
private void CleanUp(bool disposing)
{
// Be sure we have not already been disposed!
if (!this.disposed)
{
// If disposing equals true i.e. if disposed explicitly, dispose all
// managed resources.
if (disposing)
{
// Dispose managed resources.
}
// Clean up unmanaged resources here.
}
disposed = true;
}
// the below is called the destructor or Finalizer
~ClassWithDisposeAndFinalize()
{
// Call our shared helper method.
// Specifying "false" signifies that the GC triggered the cleanup.
CleanUp(false);
}

The best example which i know.
public abstract class DisposableType: IDisposable
{
bool disposed = false;
~DisposableType()
{
if (!disposed)
{
disposed = true;
Dispose(false);
}
}
public void Dispose()
{
if (!disposed)
{
disposed = true;
Dispose(true);
GC.SuppressFinalize(this);
}
}
public void Close()
{
Dispose();
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
// managed objects
}
// unmanaged objects and resources
}
}

The main difference between Dispose and Finalize is that:
Dispose is usually called by your code. The resources are freed instantly when you call it. People forget to call the method, so using() {} statement is invented. When your program finishes the execution of the code inside the {}, it will call Dispose method automatically.
Finalize is not called by your code. It is mean to be called by the Garbage Collector (GC). That means the resource might be freed anytime in future whenever GC decides to do so. When GC does its work, it will go through many Finalize methods. If you have heavy logic in this, it will make the process slow. It may cause performance issues for your program. So be careful about what you put in there.
I personally would write most of the destruction logic in Dispose. Hopefully, this clears up the confusion.

Class instances often encapsulate control over resources that are not managed by the runtime, such as window handles (HWND), database connections, and so on. Therefore, you should provide both an explicit and an implicit way to free those resources. Provide implicit control by implementing the protected Finalize Method on an object (destructor syntax in C# and the Managed Extensions for C++). The garbage collector calls this method at some point after there are no longer any valid references to the object.
In some cases, you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object. If an external resource is scarce or expensive, better performance can be achieved if the programmer explicitly releases resources when they are no longer being used. To provide explicit control, implement the Dispose method provided by the IDisposable Interface. The consumer of the object should call this method when it is done using the object. Dispose can be called even if other references to the object are alive.
Note that even when you provide explicit control by way of Dispose, you should provide implicit cleanup using the Finalize method. Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose.

I searched the answer to this question a lot today. I will share my learnings here. My answer is based on this link, because it has the clearest explanation I have seen.
When your objects has access to unmanaged resources, you have to manually release those resources. This can be done via IDisposable or finalizer meaning they both release unmanaged resources.
Rule of thumb:
Implement IDisposable to release unmanaged resources and caller code must call Dispose method. If caller forgets to call Dispose() method, you still can provide a method to release those unmanaged resources. First option is using safe handle to wrap unmanaged resource. Second option is defining a finalizer. Using safe handle is recommended way in this case.
I think this link is the clearest answer to this question. I do not know why people provide complex explanations to this question on the internet. It made me feel confused until I find that link.

As we know dispose and finalize both are used to free unmanaged resources..
but the difference is finalize uses two cycle to free the resources , where as dispose uses one cycle..

To answer on the first part you should provide examples where people use
different approach for the exact same class-object.
Otherwise it is difficult (or even strange) to answer.
As for the second question better read first this
Proper use of the IDisposable interface
which claims that
It's your choice! But choose Dispose.
In other words: The GC only knows about finalizer (if any. Also known as destructor to Microsoft).
A good code will attempt to cleanup from both (finalizer and Dispose).