Can we use Dispose method without Implementing IDisposable Interface ?
You can name a method as Dispose and use it as an ordinary method without any restrictions:
public class MyClass {
public void Dispose() {
...
}
}
...
// using() emulation
MyClass m = null;
try {
m = new MyClass();
...
}
finally {
if (m != null)
m.Dispose();
}
but if you want using() syntax you have to implement IDisposable:
public class MyNextClass: IDisposable {
protected virtual void Dispose(Boolean disposing) {
...
}
public void Dispose() {
Dispose(true);
GC.SuppressFinalize(this);
}
}
...
// compare this with the using() emulation in the code above
using (MyNextClass n = new MyNextClass()) {
...
}
Anyway, even it's possible to name a method Dispose it's not a good practice to surprize (and finally irritate) developers (including you) who read your texts; so either implement IDisposable or find some other name for the method.
Nobody will stop you from doing that but it is very poor design because everybody knows about the idisposable interface. If you give a different meaning to this method, you are obfuscating your design to whoever takes a look at your code later. Maybe even yourself in a few years where you don't remember the reason why you did this .
Managed Objects are disposed automatically even if you do not implement IDisposable, IDisposable let you dispose which runtime won't dispose like files, open handles unmanaged code components.
Implementing a Dispose Method
The pattern for disposing an object, referred to as a dispose pattern,
imposes order on the lifetime of an object. The dispose pattern is
used only for objects that access unmanaged resources, such as file
and pipe handles, registry handles, wait handles, or pointers to
blocks of unmanaged memory. This is because the garbage collector is
very efficient at reclaiming unused managed objects, but it is unable
to reclaim unmanaged objects.
If you do not want to use the IDisposable pattern and want to have your own then I believe that is not recommended way as it one would have to discover that could be obvious using IDisposable.
Related
I have been doing research on Interfaces in C# for some time now,According to MSDN
"Interfaces are better suited to situations in which your applications require many possibly unrelated object types to provide certain functionality."
https://msdn.microsoft.com/en-in/library/3b5b8ezk(v=vs.90).aspx
When implementing Dispose() instead of using Interface IDisposable I can simply define 3
methods of Dispose() & give it to the user.My Question here is "Why has Microsoft created IDisposable interface and what is the purpose of using Interface to implement Dispose()".
This is what I meant
//This method is used to release Managed Resources.
public void Dispose()
{
this.Dispose();
}
//This method is used to release both managed & unmanaged Resources.
public void DisposeAll()
{
this.Dispose();
GC.SuppressFinalize(this);
ReleaseUnmangedResources();
}
//This method is used to release only unmanaged Resources.
public void DisposeUnmanaged()
{
ReleaseUnmangedResources();
}
I am sorry if this question is too stupid or simple.Please help me in understanding interfaces.
IDisposable has special language support. Any object that implements IDisposable can be used as the subject of a using statement.
So,
using(var myDisposable = new ClassThatImplementsIDisposable())
{
//do some stuff/ even throw an exception
}//myDisposable.Dispose() is automatically called, even if an exception happened.
using statements are a very (very very) useful way to ensure that stuff gets cleaned up without having to write a whole bunch of boilerplate to ensure that it happens (even in the case of exceptions).
By providing the IDisposable interface, you are advertising that the object needs disposing. Without it, disposal might be overlooked, and tools (such as FXCop) will not pick this up.
By implementing IDisposable interface, you are telling the user of your class, that he should call Dispose() method when he is done with the class.
So the user is going to do something like this:
DisposableClass c = new DisposableClass();
//doing something
if (c is IDisposable)
c.Dispose();
Also, IDisposable objects are automatically disposed when created with using statement.
using(var c = new DisposableClass())
{
//doing something
} //c.Dispose() is called
In this case, Dispose() is called even if an exception was thrown inside the using block.
In C++, I'm used to using the sentry pattern to ensure that resources acquired are properly released when the block or function exits (see here for example). I used this, for example, for grabbing the graphics state, and then I can do whatever I want to that state, and it gets put back when the sentry object (reference) goes out of scope.
Now I'm using C#, and the same trick doesn't work, because the destructor doesn't get called until who-knows-when later.
Is there some OTHER method that is guaranteed to fire when an object's last reference is released? Or do I just have to remember to call some Restore() or Apply() or DoYourThing() method before returning from any method where I would otherwise use a sentry?
C# has finalizers, like C++, that are called when an object is destroyed. They are in the same form as C++, that is:
~ClassName()
{
}
As you know, though, C# does not have deterministic memory management, and so this isn't really a great guarantee. AS a direct result, you should not use finalizers for releasing unmanaged resources in C#. Instead, we use the IDisposable interface. This exposes a single method on the implementor, Dispose, which is intended to be called when you want to release unmanaged resources.
public class MyDisposable : IDisposable
{
public void Dispose()
{
// get rid of some expensive unmanaged resource like a connection
}
}
We can also use the using sugar to allow semantic invocation of Dispose() when the using block terminates (gracefully or not).
using(var disposable = new MyDisposable)
{
// Do something with the disposable
} // Dispose is invoked here
Should you find yourself using finalizers and Dispose, you can consider using the GC.SuppressFinalize method, although that's a bit out of my scope. There was a really good discussion elsewhere on StackOverflow about this here
This can be used to perform RAII-esque trickery, of course, such as
using(var guard = new Guard(resource))
{
}
C# provides the using block for this case, which works on any object that implements IDisposable.
For example, if you have a type class Foo : IDisposable then you can do this:
using (new Foo(/* ... */)) {
// Your code that depends on this resource.
}
This is equivalent to:
Foo x = new Foo(/* ... */);
try {
// Your code
} finally {
if (x != null) {
((IDisposable)x).Dispose();
}
}
Except, of course, that you don't have access to x. You can, however, gain such access if you need it by creating a variable in the using block:
using (Foo foo = new Foo(/* ... */)) {
// Your code that uses "foo"
}
The standard way of creating a class that can be disposed of this way or by the garbage collector is:
class Foo : IDisposable {
protected virtual void Dispose(bool disposing) {
// Your cleanup code goes here.
}
public void Dispose() {
GC.SuppressFinalize(this);
Dispose(true);
}
~Foo() {
Dispose(false);
}
}
To implement deterministic deallocation of unmanaged resources, you would use a Dispose pattern. For many cases you can combine this with a using block if you want this to occur within a specific scope.
File handles or handles to a graphics device would usually be considered a unmanaged resource. These are resources that the .NET framework does not track references for and does not automatically deallocate.
If it is managed resource, just references to C# objects/lists, then usually deterministic deallocation is not necessary, and the garbage collector can usually handle these more efficiently than you can. Don't worry so much about when managed resources are deallocated. If you no longer have a reference to them, then they should be of no concern. The concern comes when you are done with something but somehow have a lingering reference to it that is preventing the GC from deallocating it.
It sounds like what you're describing is objects that implement the IDisposable interface for C#. the IDisposable has a Dispose() method, that when defined properly on your own objects, is used to release resources.
Additionally C# does have destructors defined as such:
public class Foo
{
public Foo()
{
// constructor
}
~Foo() // destructor
}
when wrapping IDisposable objects in a using block, the Dispose() method is automatically called, the other option is to throw it in a finally block (when not using... using)
The easiest way to do this is enclosing the sentry object in a using statement. So something like this.
using (sentry = new Sentry())
{
//do your stuff here
}
After this block, sentry will have been released and out of scope.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Proper use of the IDisposable interface
I tried to find an actual answer to my question from books, internet and on stackoverflow, but nothing has helped me so far, so hopefully I can word my issue exact enough to make sense.
In general I always found the same basic usage of how to free memory, which is approx. as follows and I do understand the code itself:
public class MyClass : IDisposable
{
bool disposed = false;
public void Dispose()
{
if (!disposed)
{
Dispose(true);
GC.SuppressFinalize(this);
disposed = true;
}
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
//free managed ressources
}
// free other ressources
}
~MyClass()
{
Dispose(false);
}
}
It makes total sense the way the methods work. But now my question: Why do we need the base class IDisposable? In this code sample we define a method called Dispose(). As I read everywhere that method is part of IDisposable, but we have just defined that method within MyClass and this code would still work if we don't implement the base class IDisposable or am I wrong with this assumption?
I am not fully new to C# but there is still a lot for me to learn, so hopefully someone can lead me in the right direction here. I checked for another post with the same question, but couldn't find it, so if it does exist and it does answer my question please lead me there and I will delete this post.
You are right, as your destructor ~MyClass call Dispose, it seems there is no need for the interface IDisposable.
But Dispose is not called only by the destructor. You can call it yourself in the code when you want unmanaged resources to be disposed. It is needed because you don't know when the destructor is called (it is up to the garbage collector).
Finally, IDisposable.Dispose is called when you use a using.
using(MyDisposableClass myObject = new MyDisposableClass())
{
// My Code
}
is equivalent to:
MyDisposableClass myObject = new MyDisposableClass();
try
{
// My Code
}
finally
{
myObject.Dispose();
}
The actual implementation of IDisposable.Dispose calls the base class implementation of Dispose(bool). Anyone who inherits from this class now has the following task should they also need to dispose:
public override Dispose(bool disposing)
{
base.Dispose(disposing);
//my disposal code
}
Using this well-recognised pattern allows inheritors to extend the disposal code without breaking the disposal of the base class.
Frequently, if you don't have unmanaged resources to dispose AND can afford to seal your class, you can simplify matters with the following code:
public sealed class SomeDisposable:IDisposable
{
public void Dispose()
{
//just go ahead and clean up
//because we're sealed, no-one can ever break
//this code via inheritance
}
//~SomeDisposable()
//{
// if this is being called then it will be called
// on all referenced and unrooted IDisposables too
// If everything is managed, that means we've got nothing
// left to clean up, so we can omit this Finalizer
//}
}
Implementing IDispose gives you a place to release resources that you "hold" like streams, handles or database-connections.
Dispose() is called from the garbage collector, basically asking the object: "if there is something that you no longer need, but I can't figure out; release it now; clean up!"
In a sense comparable to the destructor in for example C++
Difference is that the C++ destructor gets called immediately and Dispose() further in time.
In most cases you don't need to implement it. The GC is clever enough to figure out in 90% of the cases how to free up used resources.
But for example: releasing the memory used by a stream doesn't automatically close the
stream and releasing a database-connection doesn't close it either.
Implementing Dispose allows you to close the file when your object is released:
internal class Something : IDisposable {
private Stream stream;
public void SomeMethod() {
stream.Write("nskdns");
}
public void Dispose() {
if (stream != null) {
stream.Close();
}
}
In addition: implementing IDispose gives you the opportunity to use the class inside a using statement:
public void Example() {
using (var x = new Something())
{
x.SomeMethod();
}
}
ensuring that x always will close the used stream when it's get free'd up by the GC.
I prefer however a dedicated Close() method on the class to allow an explicitly close of the stream instead of relying on the GC and calling Dispose()
It is used with the using block by the C# compiler.
i've read msdn and various posts about dispose pattern, and there are still a couple of things i don't understand. I've written the following code to test the dispose pattern. Please note that there aren't unmanged resources, i'm using vs2008 and .net 3.5 :
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void tryDispose()
{
//test 1 : allocate resource and leave manage it to gc
BL.myclass df = new BL.myclass();
//test 2 : try to force garbage collecting
//GC.Collect();
//test 3 : call dispose myself
//using (BL.myclass df = new BL.myclass())
//{
//}
}
private void button1_Click(object sender, EventArgs e)
{
tryDispose();
}
this is my disposable class:
class myclass: IDisposable
{
private StronglyTypedDs myDS;
private bool _disposed;
public myclass()
{
using (myDSTableAdapter docDocadpt = new myDSTableAdapter())
{
myDS = new StronglyTypedDs();
docDocadpt.Fill(myDS.TheTable);
}
}
#region IDisposable Members
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~myclass()
{
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
if (myDS != null)
myDS .Dispose();
myDS = null;
}
}
_disposed = true;
}
#endregion
}
The results are :
test 1a - just instantiating myclass, the destructor is commentend since myclass doesn't contains unmanaged resources : myclass.dispose is not called, even if i close the application (whose dispose is executed instead) . So what's the state of the dataset once i close the application ?
test 1b - uncommenting destructor, it's ok all disposes are called when i close the application.
test 2a and 2b - i do the above test just calling gc.collect : the behaviour is identical to test 1a and 1b respectively
test 3 - everything works fine (of course)
many posts says that, if myclass doesn't contains unmanaged resources, i don't need to add the destructor; yet in my tests , if i don't add the destructor , myclass.dispose doesn't get called when i close the application. I haven't waited for the gc to run by itself (if i remember correctly gc.collect doesn't guarantes the class instance is deallocated) to check if it will call myclass.dispose .
So what's the correct implemention : always define e destructor or avoid it if myclass contains only managed resources ?
If i had filled all generations levels, would had the gc called myclass dispose or not without having implemented a destructor?
Finally i've noticed that if i define a destructor , but don't declare the class as implementing IDisposable, the disposing chain works anyway. This could make sense since the destructor might be translated to finalize in IL. But i find it really confusing : is it some kind of "implicit" interface implementation i don't know? gc can dispose the item but users can't
thank you in advance
Stefano
Trust your Garbage Collector. Managed resources will get cleaned up, eventually. There is no need for a finalizer or implementing IDisposable unless you have some external resource that needs to be released.
This typically means that you only should implement IDisposable when you either:
Are wrapping a native resource. (In this case, you probably also want a finalizer.)
Are encapsulating a class which implements IDisposable. (In this case, you want IDisposable, but don't need to implement a finalizer/destructor.)
Part of the confusion with IDisposable, in my opinion, is that it covers quite a few use cases, and the proper implementation changes depending on what you're doing (ie: wrapping native resources, wrapping other IDisposable classes, or using Factored types). To address this, I've written a multiple part series on IDisposable - it might help clarify some of this for you.
The correct pattern is to only use a finalizer when your class contains unmanaged resources. As to relying on the GC to dispose of your managed objects, don't. The IDisposable contract makes it clear that this object needs to be disposed.
Ok i think i've understood, referring to my example its correct to implement a dispose because the dataset is global to my class and implements IDisposable , while i don't need the finalizer because there aren't unmanaged resources.
Even if i "forget" to dispose some managed resource in my class dispose method, the gc will collect it at some point. The dispose method is just an utility i provide to other classes/developers for managed resources, a must with the finalizer if i wrap unmanaged resources .
i'll read the articles you have provided asap, but in the mean time i've the last question : when gc will free memory owned by my class and its resources ? when someone calls dispose or when it will run (it will free memory instead of moving it to next generation ) ?
thank you everybody for your answers and examples
I wrote a brief seris entitled How to Implement IDisposable and Finalizers: 3 Easy Rules. It describes a much simpler approach that Microsoft themselves have followed since the 2.0 version of the BCL.
The "official" pattern is needlessly complex and needlessly confusing.
Your code is correct, you've implemented it exactly like it is documented in the MSDN library.
You'll need to take a second look though. Reason what happens when the destructor (aka finalizer) runs. The disposing argument will be false, the protected Dispose method does nothing. This is entirely normal, finalizers should only ever release unmanaged resources. You don't have any. It is extraordinary rare to ever have an unmanaged resource in your own code. They belong in the nice wrapper classes available in .NET to turn an unmanaged operating resource into a nice managed class. If you find yourself thinking you need a finalizer, you'll be wrong 99.99% of the time. Even if you do wrap an unmanaged resource, you should use one of the SafeHandle wrappers. And rely on their finalizers.
Okay, you want to get rid of the destructor. It isn't healthy to leave it in, it keeps the object in memory longer than necessary. When you do, you'll cut it down to:
public void Dispose()
{
if (myDS != null) myDS.Dispose();
}
Which is the boiler-plate implementation of most any Dispose() method, just call the Dispose method of members of the class. You can completely omit it if you don't have any members with a Dispose() method.
Next, you do misunderstand how the Dispose() method gets called. It is not automatic. Which is the point of having it in the first place, releasing resources automatically is already taken care of by the garbage collector. The Dispose() method is there for you to call, either with the using statement or calling it directly. So that you can release the resource early instead of waiting for the garbage collector finalizer thread to get around to it. Which can take a while. Call it when you know that your program won't be using the object anymore.
If your DataSet is actively used by the form then you cannot dispose it until the form closes. Call the class' Dispose() method in a FormClosed event handler. Or, better, open the form's Designer.cs file, cut-and-paste the Dispose() method you find in there and move it to the form's source code file. And add the dispose call. I know that's a bit confuzzling, but the only time it's okay to edit the designer file.
The main purpose of IDisposable is to have a consistent standard interface you can dispose of unmanaged resources with, that is if you didn't do something to ensure Dispose() was called these resources would hang around after the app was closed. Also understood by the using() syntax, that is using will implement the following block for you:
DisposableType someDisposable = new DisposableType();
try
{
// Do whatever
}
finally
{
((IDisposable)someDisposable).Dispose();
}
This is all implemented in a nice design like so:
using(DisposableType someDisposable = new DisposableType())
{
// Do whatever
}
I have a C# object with a critical resource that needs to be flushed very specific points in time making it a bad candidate to leave around for the garbage collector to take care of whenever it gets around to it, how should I handle this? Is there something like C++'s delete operator that will let me manually kill the instance of this object when needed?
You are looking for IDisposable. Here is an example class that implements this.
class MyDisposableObject : IDisposable
{
public MyDisposableObject()
{
}
~MyDisposableObject()
{
Dispose(false);
}
private bool disposed;
private void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
// Dispose of your managed resources here.
}
// Dispose of your unmanaged resources here.
this.disposed = true;
}
}
void IDisposable.Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
}
To use it, you can do something like this:
public void DoingMyThing()
{
using (MyDisposableObject obj = new MyDisposableObject())
{
// Use obj here.
}
}
The using keyword makes sure that the Dispose() method on IDisposable gets called at the end of its scope.
The IDisposable interface exists for deterministic destruction. There's a pattern for implementing it correctly on MSDN.
In tandem, you should also consider using the using statement when your object's lifetime does not span multiple scopes.
This is precisely what the IDiposable interface is for. You release the critical resources in the Dispose() method, and then leave the object around for the garbage disposer to deal with deallocating the memory.
Google for the IDisposable interface. This is the only mechanism available to you. It's tailor made if your critical resource is unmanaged. If it's a managed resource, could you be more specific about what needs to be "flushed".
The IDisposable interface was added to support deterministic destruction in C++/CLI, and you can use it from any .NET language. It's what you want.
If you are talking about a specific managed resource that you feel "MUST" be released at a specific time, you could specifcally call the Garbage Collectors' Collect method, after de-referencing the object, but there are performance considerations to be thought of, as normally the garbage collector knows when to collect items. And in general it is a bad idea.
As others are mentioning above, the IDisposable pattern is helpful for releasing unmanaged resources when needed.
NOTE: I'm going to repeat, you COULD call GC.Collect() but it is NOT a good thing, but a valid answer for the question!