I have Class A that implements the Disposable pattern in order to release unmanaged resources such as unsubscribing from events. Class B uses Class A, but does not wrap it in a using {..} block nor explicity calls A.Dispose(true) so A.dispose is called in A's finalizer via the standard Dispose(false) call. But then by setting the bool parameter to false, the unmanaged resources will not be cleaned up, i.e not unsubscribing from subscribed events. Shouldn't the finalizer be calling Dispose(true) or should Class B explicitly call A.Dispose(true) at some point such as in its own finalizer?
private bool _disposed = false; // To detect redundant calls
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
_promotionsSQLTableDependency.Stop();
_awardsSQLTableDependency.Stop();
_progressiveGeneratorService.OnProgressiveLevelsUpdate -= _progressiveUpdateHandler;
}
_disposed = true;
}
}
~PromotionHandler()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
implements the Disposable pattern in order to release unmanaged resources such as unsubscribing from events.
Unsubscribing from an event isn't an unmanaged resource that needs to be cleaned up though.
Class B uses Class A, but does not wrap it in a using {..} block nor explicity calls A.Dispose(true)
You should treat that as a bug in your program. The whole point of implementing IDisposable is because that object needs to be explicitly cleaned up with the owner(s) are finished with it.
But then by setting the bool parameter to false, the unmanaged resources will not be cleaned up,
But those aren't unmanaged resources, which is why they aren't cleaned up in the finally block.
Shouldn't the finalizer be calling Dispose(true) or should Class B explicitly call A.Dispose(true) at some point such as in its own finalizer?
No. You shouldn't be interacting with managed objects in the finalizer. It's not safe to do so. Since you have no unmanaged resources to clean up in a finalizer, you shouldn't even have a finalizer.
The dispose method must only use the disposing parameter to decide whether to free managed resources. Unmanaged resources must always be freed.
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
// Free managed resources
}
// always free unmanaged resources
_disposed = true;
}
}
if the Dispose call happens via the garbage collector (=via a call to the Finalizer) and the disposing is false, you don't need to free the managed resources. The garbage collector will also call the Finalizer of those managed objects (maybe even earlier).
This is what the documentation says:
In the second overload, the disposing parameter is a Boolean that
indicates whether the method call comes from a Dispose method (its
value is true) or from a finalizer (its value is false).
The body of the method consists of two blocks of code:
A block that frees unmanaged resources. This block executes regardless of the value of the disposing parameter.
A conditional block that frees managed resources. This block executes if the value of disposing is true. The managed resources that
it frees can include:
Managed objects that implement IDisposable. The conditional block can be used to call their Dispose implementation. If you have used a
safe handle to wrap your unmanaged resource, you should call the
SafeHandle.Dispose(Boolean) implementation here.
Managed objects that consume large amounts of memory or consume scarce resources. Freeing these objects explicitly in the Dispose
method releases them faster than if they were reclaimed
non-deterministically by the garbage collector.
If the method call comes from a finalizer (that is, if disposing is
false), only the code that frees unmanaged resources executes. Because
the order in which the garbage collector destroys managed objects
during finalization is not defined, calling this Dispose overload with
a value of false prevents the finalizer from trying to release managed
resources that may have already been reclaimed.
What about below disposable pattern?
using System;
public class MyClass : IDisposable
{
public void Dispose()
// Implement IDisposable
{
//just do the cleanup
GC.SuppressFinalize(this);
}
}
Update
I meant to say, if there are no un-managed resources do I need finalizer? Isn't the above disposable pattern is good enough? Yes, even though users/developers doesn't invoke dispose, doesn't GC invoke dispose by default?
And what about the order in which GC invokes dispose and finalizers?
Please see this question for more details.
In other words, when we have finalizer, why do we call Dispose with false as parameter?
From http://msdn.microsoft.com/en-us/magazine/cc163392.aspx#S2, looks like its always advisable to release unmanaged resources from finalizer and not the managed references.
It's always recommended to release unmanaged resources from Dispose method. I still didn't get the total gist when reading the article.
But if there are no unmanaged resources, the below pattern should work.
According to msdn.microsoft.com/en-us/magazine/cc163392.aspx#S2, msdn.microsoft.com/en-us/library/fs2xkftw.aspx it's recommended to release native resources in finalizer and all of them with dispose(). If dispose() is called explicitly, it can suppress finalizer i.e. if there no native resources, we don't need finalizer.
using System;
public class MyClass : IDisposable
{
private bool disposed = false;
protected virtual void Dispose(bool suppressFinalize)
{
if (!disposed)
{
//Just do the cleanup
//and release resources
disposed = true;
}
if (!suppressFinalize)
{
GC.SuppressFinalize(this);
}
}
public void Dispose()
// Implement IDisposable
{
Dispose(true);
}
~MyClass() // the finalizer
{
Dispose(false);
}
}
Because you might have direct references to unmanaged resources (e.g. Windows handles) and you want to release them even if no-one calls Dispose.
This is very rare though - usually you only really have indirect references to unmanaged resources, via other managed types which will have finalizers if they need them.
Finalization + IDisposable in .Net is really two distinct problems which are attempted to be solved with the single disposable pattern.
Managed resource cleanup
Unmanaged resource cleanup
Unmanaged resources are items which aren't in the control of the CLR and garbage collector. Items like file handles, memory returned from PInvoke, etc ... If these resources aren't explicitly freed by user code they will leak and be around for the remainder of the process lifetime. It's critical that they are freed.
This is where the finalizer comes in. It will run on an object just before it is collected by the CLR. This doesn't require the consumer follow the disposable pattern and hence is a good fallback for ensuring unmanaged resources are freed to prevent a leak.
If your code doesn't contain any directly held unmanaged resources then there is no reason to have a finalizer. It is the responsibility of the code which holds the unmanaged resource to have the finalizer.
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
I have been programming in .NET for four years (mostly C#) and I use IDiposable extensively, but I am yet to find a need for a finaliser. What are finalisers for?
A finalizer is a last ditch attempt to ensure that something is cleaned up correctly, and is usually reserved for objects that wrap unmanaged resources, such as unmanaged handles etc that won't get garbage collected.
It is rare indeed to write a finalizer. Fortunately (and unlike IDisposable), finalizers don't need to be propagated; so if you have a ClassA with a finalizer, and a ClassB which wraps ClassA, then ClassB does not need a finalizer - but quite likely both ClassA and ClassB would implement IDisposable.
For managed code, IDisposable is usually sufficient. Even if you don't clean up correctly, eventually the managed objects will get collected (assuming they are released).
Finalizers are only for freeing unmanaged resources like GDI bitmap handles for example. If you don't allocate any unmanaged resources then you don't need finalizers. In general it's a bad idea to touch any managed object in a finalizer because the order of finalization is not guaranteed.
One other useful technique using a finalizer is to assert that Dispose has been called when the application is required to do so. This can help catch coding errors in a DEBUG build:
void Dispose()
{
GC.SuppressFinalize(this);
}
#if DEBUG
~MyClass()
{
Debug.Fail("Dispose was not called.");
}
#endif
Finalizers are meant as a mechanism to release resources not controlled by garbage collector, like an unmanaged handle. While Dispose might do it, it isn't guaranteed that the consumer will call it.
Finalizers are for cleaning up resources if they were not disposed.
IE, nothing enforces that you ever call Dispose(), but Finalizers are called automatically by the garbage collector.
This functionality should not be relied upon, as there is no guarantee when (or if) garbage collection will get to your object.
Wikipedia says:
...a finalizer is a piece of code that
ensures that certain necessary actions
are taken when an acquired resource...
is no longer being used [because the
owning object has been garbage
collected]
And if you're not using a finaliser when you're writing IDisposables you've quite possibly got memory leaks, because there's no guarantee an owner is actually going to call Dispose().
MS themselves recommend you write something similar to this into your implementers:
public void Dispose()
{
this.Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
if (!this.isDisposed)
{
if (disposing)
{
GC.SuppressFinalize(this);
}
}
//Dispose of resources here
this.isDisposed = true;
}
~DisposableSafe()
{
this.Dispose(false);
}
private bool isDisposed = false;
Personally, I can't stand the copy-paste so I tend to wrap that in an abstract class for reuse.
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).