I can never remember all the rules for implementing the IDisposable interface, so I tried to come up with a base class that takes care of all of this and makes IDisposable easy to implement. I just wanted to hear your opinion if this implementation is ok as it is or whether you see something I could improve. The user of this base class is supposed to derive from it and then implement the two abstract methods ReleaseManagedResources() and ReleaseUnmanagedResources(). So here is the code:
public abstract class Disposable : IDisposable
{
private bool _isDisposed;
private readonly object _disposeLock = new object();
/// <summary>
/// called by users of this class to free managed and unmanaged resources
/// </summary>
public void Dispose() {
DisposeManagedAndUnmanagedResources();
}
/// <summary>
/// finalizer is called by garbage collector to free unmanaged resources
/// </summary>
~Disposable() { //finalizer of derived class will automatically call it's base finalizer
DisposeUnmanagedResources();
}
private void DisposeManagedAndUnmanagedResources() {
lock (_disposeLock) //make thread-safe
if (!_isDisposed) { //make sure only called once
try { //suppress exceptions
ReleaseManagedResources();
ReleaseUnmanagedResources();
}
finally {
GC.SuppressFinalize(this); //remove from finalization queue since cleaup already done, so it's not necessary the garbage collector to call Finalize() anymore
_isDisposed = true;
}
}
}
private void DisposeUnmanagedResources() {
lock (_disposeLock) //make thread-safe since at least the finalizer runs in a different thread
if (!_isDisposed) { //make sure only called once
try { //suppress exceptions
ReleaseUnmanagedResources();
}
finally {
_isDisposed = true;
}
}
}
protected abstract void ReleaseManagedResources();
protected abstract void ReleaseUnmanagedResources();
}
I can't really comment on the correctness of your code, but I question whether you'll find having the Disposable class at the base of your inheritance tree as flexible as it needs to be. It's won't be much use when you want to inherit from something you don't own. I think that IDispoasble is left as an interface because of the many different domains across which it might be used. Providing a concrete implementation at the foot of the inheritance hierarchy would be... limiting.
You are accessing the managed object _disposeLock in the finalizer. It may have already been garbage-collected by then. Not sure what the implications of this would be as you are only using it to lock.
Thread-safety seems like overkill. I don't think you need to worry about contention between the GC thread and your application thread.
Otherwise it looks correct.
EDIT Yes, I misread the portion about separating disposing managed and unmanaged resources (still on first cup of coffee).
However the lock is still almost certainly not necessary. Yes, during a passive dispose the code will be running on the finalizer thread which is different than the thread it originally ran on. However if the object is being finalized in this fashion the CLR has already determined there are no existing references to this object and hence collected it. So there is no other place which can be calling your dispose at that time and hence there is no reason for a lock.
A couple of other style comments.
Why make the methods abstract? By doing so you are forcing derived classes to implement methods to dispose of managed and unmanaged resources even if they don't have any to dispose. True there is no point in deriving from this class if you don't have anything to dispose. But I think it's fairly common to only have one or the other but not both. I would make them virtual vs. abstract.
Also you prevent double dispose but you do nothing to warning the developer that they are double disposing an object. I realize the MSDN documentation says that double dispose should be essentially a no-op but at the same time under what circumstances should this be legal? In general it's a bad idea to access an object after it's been disposed. A double dispose necessitates a disposed object being reused and is likely a bug (this can happen if finalization is not suppressed in an active dispose but that's also a bad idea). If I were implementing this I would throw on double dispose to warn the developer they were using an object incorrectly (that is using it after it was already disposed).
If you are concerned about the thread safety then I'd use the lightweight interlocked operations rather than a heavyweight lock:
class MyClass: IDispose {
int disposed = 0;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
public virtual void Dispose(bool disposing)
{
if (0 == Thread.InterlockedCompareExchange(ref disposed, 1, 0))
{
if (disposing)
{
// release managed resources here
}
// release unmanaged resources here
}
}
~MyClass()
{
Dispose(false);
}
}
Related
If Finalizer (destructor) is implemented in a class and GC.SupressFinalizer() is called from the overriden Dispose() method will the Garbage Collector still take care of any managed resources the instances of that class might have?
What confuses me is Microsofts documentation on this matter. For example the implemenation of IDisposable pattern in the virtual Dispose method takes care of the managed resources as well as the unmanaged. Why is that being done if the GC is taking care of the managed resources by default?
If I define a class like this:
public class Car
{
string plateNum;
}
and use this type as a filed in a class that also deals with unmanaged resources, according to the Microsofts documentation, the proper way to handle the disposal of the objects would be to call Dispose on the Car as well. For one to do so Car has to implement the IDisposable interface. Car is only dealing with the managed resources, there is no reason for doing so in the Car class, I have no idea what Dispose() would even do there, maybe give null to the plateNum? Also why would anyone want to implement IDisposable on the class that deals with the managed resources only?
Having that in mind, why is there a section in the code in the virtual Dispose() method (in the example in the MS documentation) in which managed resources are disposed?
protected virtual void Dispose(bool disposing)
{
// Check to see if Dispose has already been called.
if(!this.disposed)
{
// If disposing equals true, dispose all managed
// and unmanaged resources.
if(disposing)
{
// Dispose managed resources.
component.Dispose();
}
// Call the appropriate methods to clean up
// unmanaged resources here.
// If disposing is false,
// only the following code is executed.
CloseHandle(handle);
handle = IntPtr.Zero;
// Note disposing has been done.
disposed = true;
}
}
The only reason that I can think of is that GC.SupressFinalize(Object) is telling to the GC that it doesn't need to take care of anything related to the object argument that is given. But this shouldn't be the case because implementing the finalizer should only mean that the object that implements it should be put on the Finalizer queue only after the object has been dealt with by the GC because the Finalizer method, that is explicitly implemented by the user, should be called.
Also if a finalizer is defined does that change the way the GC collects the managed resources that the instance contains or does it just mean that additional code contained in the finalizer will be executed?
There are many Q+A about this already on SO so I'll give you a very practical answer: You won't ever need to write a finalizer.
Summary: In the rare case that you have an unmanaged resource, use the SafeHandle class to make it a managed resource.
When you inspect the full pattern carefully you can see that without unmanaged resources the destructor (aka the Finalizer, ~MyClass() {}) code path does exactly nothing.
And actually having that Finalizer without SuppressFinalize() is very expensive, it will delay the cleanup of your object to the next GC. Promoting its data to gen 1.
The remaining reason for the full pattern with virtual void Dispose(bool) is inheritance. A resource holding class should almost never need that. So make it sealed and all you need (want) is:
public sealed MyClass : IDisposable
{
private SomeResource _myResource;
public void Dispose()
{
_myResource?.Dispose();
}
}
And when you need inheritance then this is the official pattern.
I've read carefully through this article and it seems to clearly state that the dispose pattern should be implemented in all cases of IDisposable implementation. I'm trying to understand why I need to implement the dispose pattern in cases when my class holds only managed resources (i.e. other IDisposable members or safe handles). Why cannot I just write
class Foo : IDisposable
{
IDisposable boo;
void Dispose()
{
boo?.Dispose();
}
}
If it's definitely known that there are no unmanaged resources and there is no point to call Dispose method from finalizer as managed resources aren't being freed from finalizer?
Update: In order to add some clarity. The discussion seems to come down to the question whether it's needed to implement the dispose pattern for every base public non-sealed class which implements IDisposable or not. I however cannot find potential problems with hierarchy when a base class without unmanaged resources doesn't use dispose pattern while child classes which have unmanaged resources do use this pattern:
class Foo : IDisposable
{
IDisposable boo;
public virtual void Dispose()
{
boo?.Dispose();
}
}
// child class which holds umanaged resources and implements dispose pattern
class Bar : Foo
{
bool disposed;
IntPtr unmanagedResource = IntPtr.Zero;
~Bar()
{
Dispose(false);
}
public override void Dispose()
{
base.Dispose();
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing)
{
// Free any other managed objects here.
//
}
// close handle
disposed = true;
}
}
// another child class which doesn't hold unmanaged resources and merely uses Dispose
class Far : Foo
{
private IDisposable anotherDisposable;
public override void Dispose()
{
base.Dispose();
anotherDisposable?.Dispose();
}
}
Even more, for me it looks as better separation of concerns when implementations are responsible only for those things which they are aware of.
This
private class Foo : IDisposable
{
IDisposable boo;
public void Dispose()
{
boo?.Dispose();
}
}
Is perfectly fine. As is
public sealed class Foo : IDisposable
{
IDisposable boo;
public void Dispose()
{
boo?.Dispose();
}
}
What could go wrong if I have public not sealed base class implemented as above with virtual Dispose method ?
From the docs:
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.
Accessing a managed object that has already been reclaimed, or accessing its properties after it's been Disposed (perhaps by another finalizer) will cause an Exception to be raised in the Finalizer, which is bad:
If Finalize or an override of Finalize throws an exception, and the
runtime is not hosted by an application that overrides the default
policy, the runtime terminates the process and no active try/finally
blocks or finalizers are executed. This behavior ensures process
integrity if the finalizer cannot free or destroy resources.
So if you had:
public class Foo : IDisposable
{
IDisposable boo;
public virtual void Dispose()
{
boo?.Dispose();
}
}
public class Bar : Foo
{
IntPtr unmanagedResource = IntPtr.Zero;
~Bar()
{
this.Dispose();
}
public override void Dispose()
{
CloseHandle(unmanagedResource);
base.Dispose();
}
void CloseHandle(IntPtr ptr)
{
//whatever
}
}
~Bar -> Bar.Dispose() -> base.Dispose() -> boo.Dispose() But boo may have been reclaimed by the GC.
I haven't seen this particular usage of Dispose mentioned yet, so I thought I'd point out a common source of memory leaks when not using the dispose pattern.
Visual Studio 2017 actually complains about this via static code analysis that I should "implement the dispose pattern". Do note I'm using SonarQube and SolarLint, and I don't believe Visual Studio will catch this alone. FxCop (another static code analysis tool) likely will, although I didn't test that.
I note the below code to showcase the dispose pattern is also there to protect against something like this, which has no unmanaged resources:
public class Foo : IDisposable
{
IDisposable boo;
public void Dispose()
{
boo?.Dispose();
}
}
public class Bar : Foo
{
//Memory leak possible here
public event EventHandler SomeEvent;
//Also bad code, but will compile
public void Dispose()
{
someEvent = null;
//Still bad code even with this line
base.Dispose();
}
}
The above illustrates very bad code. Don't do this. Why is this horrific code? That's because of this:
Foo foo = new Bar();
//Does NOT call Bar.Dispose()
foo.Dispose();
Let's assume this horrific code was exposed in our public API. Consider the above classes used by consumers of it:
public sealed class UsesFoo : IDisposable
{
public Foo MyFoo { get; }
public UsesFoo(Foo foo)
{
MyFoo = foo;
}
public void Dispose()
{
MyFoo?.Dispose();
}
}
public static class UsesFooFactory
{
public static UsesFoo Create()
{
var bar = new Bar();
bar.SomeEvent += Bar_SomeEvent;
return new UsesFoo(bar);
}
private static void Bar_SomeEvent(object sender, EventArgs e)
{
//Do stuff
}
}
Are the consumers perfect? No.... UsesFooFactory should probably also unsubscribe from the event. But it does highlight a common scenario where an event subscriber outlives the publisher.
I've seen events cause countless memory leaks. Especially in very large or extreme high performance codebases.
I can also hardly count how many times I've seen objects live long past their time of disposal. This is a very common way many profilers find memory leaks (disposed objects still held onto by a GC Root of some kind).
Again, overly simplified example and horrible code. But it's really never good practice to call Dispose on an object and not expect it to dispose the entire object, whether it has been derived from a million times or not.
Edit
Please note this answer is intentionally only addressing managed resources, showcasing that the dispose pattern is useful in this scenario as well. This purposefully does not address the use case for unmanaged resources as I felt there was a lack of focus on managed only uses. And there are many other good answers on here that talk about that.
I will, however, note a few quick things that are important when it comes to unmanaged resources. The above code might not address unmanaged resources, but I want to make clear it does not contradict how they should be handled.
It's extremely important to use finalizers when your class is responsible for unmanaged resources. Briefly, finalizers are automatically called by the Garbage Collector. So it gives you a reasonable guarantee that it always gets called at some point in time. It's not bulletproof, but a far cry from hoping user code calls Dispose.
This guarantee is not true of Dispose. An object can be reclaimed by the GC without Dispose ever being called. That's the key reason finalizers are used for unmanaged resources. The GC itself only handles managed resources.
But I will also note it's equally important finalizers should not be used to clean up managed resources. There are countless reasons why (it's the GC's job to do this after all) but one of the largest drawbacks to using finalizers is delaying garbage collection on an object.
The GC, seeing an object is free to reclaim but has a finalizer, will delay the collection by placing the object in the finalizer queue. This adds significant unnecessary lifetime to an object, plus more pressure on the GC.
Finally I'll note that finalizers are non-deterministic for this reason, despite having similar syntax to something like a destructor in C++. They are very different beasts. You should never rely upon a finalizer to clean up unmanaged resources at a specific point in time.
You probably got it wrong. You don't need to implement finilizer if you don't have unmanaged resources. You can check it by using automatic pattern implementation in Visual Studio (it will even generate the comments saying that you should uncomment the finalizer ONLY if you use unmanaged resources).
The dispose pattern is used only for objects that access unmanaged resources.
If you design a base class and some of the inheriting classes access unmanaged resources, the inheriting classes will deal with it themselves by overriding Dispose(bool) and defining the finalizer.
It's explained in this article, all finalizers will be called anyway if not suppressed. And if suppressed everything would have been released by the chain of Diapose(true) calls in the first place.
If Dispose() is implemented using a public virtual method, derived classes that expect to override that method can do so and all will be well. If, however, anything on the inheritance chain implements IDisposable.Dispose() via means other than overriding the public virtual Dispose() method, that can make it impossible for a sub-derived class to implement its own IDisposable.Dispose() while still being able to access the parent implementation.
The Dispose(bool) pattern can be used regardless of whether or not there is a public Dispose() method, and thus avoids the need to have separate patterns for the cases where a class does or does not expose a public Dispose() method. The GC.SuppressFinalize(this) could generally be replaced by a GC.KeepAlive(this), but for classes without finalizers the cost is about the same. In the absence of that call, the finalizers for any objects to which a class holds a reference could get triggered while the class' own Dispose method is running. Not a likely scenario, nor one that would usually cause problems even if it occurs, but passing this to GC.KeepAlive(Object) or GC.SuppressFinalize(Object) makes such quirky situations impossible.
This question already has answers here:
Minimal IDisposable implimenation for managed resources only
(3 answers)
Closed 7 years ago.
I know that the general guideline for implementing the dispose pattern warns against implementing a virtual Dispose(). However, most often we're only working with managed resources inside a class and so the full dispose pattern seems like an overkill - i.e. we don't need a finalizer. In such cases, is it OK to have a virtual Dispose() in the base class?
Consider this simple example:
abstract class Base : IDisposable
{
private bool disposed = false;
public SecureString Password { get; set; } // SecureString implements IDisposable.
public virtual void Dispose()
{
if (disposed)
return;
if (Password != null)
Password.Dispose();
disposed = true;
}
}
class Sub : Base
{
private bool disposed = false;
public NetworkStream NStream { get; set; } // NetworkStream implements IDisposable.
public override void Dispose()
{
if (disposed)
return;
if (NStream != null)
NStream.Dispose();
disposed = true;
base.Dispose();
}
}
I find this more readable than a complete dispose pattern. I understand that this example would become problematic if we introduced an unmanaged resource into the Base class. But suppose that this won't happen. Is the above example then valid/safe/robust, or does it pose any problem? Should I stick to the standard full-blown dispose pattern, even if no unmanaged resources are used? Or is the above approach indeed perfectly OK in this situation - which in my experience is far more common than dealing with unmanaged resources?
I have given up on the full-blown IDisposable pattern in cases where I am not dealing with unmanaged resources.
I don't see any reason why you shouldn't be able to forego the pattern and make Dispose virtual if you can ensure that derived classes won't introduce unmanaged resources!
(And here lies a problem, because you cannot enforce this. You have no control over what fields a derived class will add, so there is no absolute safety with a virtual Dispose. But then even if you used the full-blown pattern, a derived class could get things wrong, so there is always some trust involved that subtypes adhere to certain rules.)
First, in cases where we only deal with managed objects, having a finalizer would be pointless: If Dispose is called from the finalizer (Dispose(disposing: false) according to the full-blown pattern), we may not safely access/dereference other reference-typed managed objects because they might already be gone. Only value-typed objects reachable from the object being finalized may be safely accessed.
If the finalizer is pointless, it is also pointless to have the disposing flag, which is used to distinguish whether Dispose was explicitly called or whether it was called by the finalizer.
It is also unnecessary to do GC.SuppressFinalize if there is no finalizer.
I am not even sure whether it is then still imperative that Dispose not throw any exceptions in a managed-only scenario. AFAIK this rule exists mostly to protect the finalizer thread. (See #usr's comment below.)
As you can see, once the finalizer goes, much of the classic Disposable pattern is no longer necessary.
I understand that this example would become problematic if we introduced an unmanaged resource into the Base class. But suppose that this won't happen. Is the above example then valid/safe/robust, or does it pose any problem? Should I stick to the standard full-blown dispose pattern, even if no unmanaged resources are used?
Though your base class uses exclusively managed resources (and this will not change in the future), you cannot guarantee that a derived class will not use unmanaged resources. So consider to implement the Basic Dispose Pattern in your base class (a class with a virtual Dispose(bool) but without a finalizer) even if you always call the Dispose(bool) method with true.
When some day a new subclass will be derived from your Base, which uses unmanaged resources, its finalizer might want to call the Dispose(bool) with false. Of course, you could introduce a new Dispose(bool) in the derived class:
public class SubUnmanaged : Base
{
IntPtr someNativeHandle;
IDisposable someManagedResource;
public override sealed void Dispose()
{
base.Dispose();
Dispose(true);
GC.SuppressFinalize(this);
}
~SubUnmanaged();
{
base.Dispose();
Dispose(false);
}
protected virtual void Dispose(bool disposing)
{
if (someNativeHandle != IntPtr.Zero)
Free(someNativeHandle);
if (disposing)
someManagedResource.Dispose();
}
}
But I think this is a little bit nasty. By sealing the original virtual Dispose() method, you can prevent the further inheritors to be confused because of the multiple virtual Dispose methods, and you can call the common base.Dispose() both from the finalizer and the sealed Dispose(). You must do the same workaround in every subclass, which use unmanaged resources and is derived from Base or a fully managed subclass. But this is already far from the pattern, which always makes the things difficult.
I have this 'PlayerClass' class and every time I instantiate it I need to dispose of it, including the fields inside that class. Is there a way to do it? This is my class:
internal class PlayerClass
{
public WindowsMediaPlayer _wplayer;
}
How do I get to dispose of the class after using it?
I have tried to find a way on the internet but none of them are working after testing it.
I've tried this:
internal class PlayerClass : IDisposable
{
public WindowsMediaPlayer _wplayer;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
/// <summary>
/// Is this instance disposed?
/// </summary>
protected bool Disposed { get; private set; }
/// <summary>
/// Dispose worker method. See http://coding.abel.nu/2012/01/disposable
/// </summary>
/// <param name="disposing">Are we disposing?
/// Otherwise we're finalizing.</param>
protected virtual void Dispose(bool disposing)
{
Disposed = true;
}
}
What am I doing wrong?
It looks as if you're implementing IDisposable just for the heck of it which is not necessary for managed code. The garbage collector will automatically clean up behind you.
You may need to clarify in your post why you are implementing IDisposable.
However I believe your mistake is that Dispose() is not automatically called by the garbage collector. If you do implement IDisposable you must make sure that the code using your class either instantiates inside a using() statement or manually calls .Dispose. Otherwise your dispose method will never fire.
using(var player = new PlayerClass()){
// Do something with player
// player.Dispose() is called automatically when you exit this using statement.
}
Since you're relying on the caller to make sure Dispose is called you may also want to look into a SafeHandle (preferred) or Finalize.
Because the IDisposable.Dispose implementation is called by the
consumer of a type when the resources owned by an instance are no
longer needed, you should either wrap the managed object in a
SafeHandle (the recommended alternative), or you should override
Object.Finalize to free unmanaged resources in the event that the
consumer forgets to call Dispose.
Source: IDisposable Interface
Using Statement
https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/using-statement
Contrary to the advice of the other answers, it is necessary and essential to Dispose of all created objects that implement a Dispose() method (ie implement IDisposable). These objects are unmanaged resources, and thus are invisible to the GC. Not disposing of them is a guaranteed memory leak.(Note that some terminology prefers a Close() method to a Dispose method, in which case the Close() method should be identical.)
Here is a best practice implementation of the IDisposable interface.
#region IDisposable implementation with finalizer
private bool isDisposed = false;
public void Dispose() { Dispose(true); GC.SuppressFinalize(this); }
protected virtual void Dispose(bool disposing) {
if (!isDisposed) {
if (disposing) {
if (_wplayer != null) _wplayer.Dispose();
}
}
isDisposed = true;
}
#endregion
Here are the Best Practices Dos and Donts from the MSDN link above:
DO declare a protected virtual void Dispose(bool disposing) method to
centralize all logic related to releasing unmanaged resources.
DO implement the IDisposable interface by simply calling Dispose(true) followed by GC.SuppressFinalize(this).
DO NOT make the parameterless Dispose method virtual.
DO NOT declare any overloads of the Dispose method other than Dispose() and Dispose(bool).
DO allow the Dispose(bool) method to be called more than once. The method might choose to do nothing after the first call.
AVOID throwing an exception from within Dispose(bool) except under critical situations where the containing process has been corrupted (leaks, inconsistent shared state, etc.).
CONSIDER providing method Close(), in addition to the Dispose(), if close is standard terminology in the area.
From the MSDN documentation.
Provides a mechanism for releasing unmanaged resources.
You do not need to dispose managed objects. .Net will lead with this for you. It is usefull when you create a interop classes which will lead with unmanaged resources, then you can dispose all objects.
Are there some advices about how I should deal with the IDisposable object sequences?
For example, I have a method that builds a IEnumerable<System.Drawing.Image> sequence and
at some point I would need to dispose that objects manually, because otherwise this might lead to some leaks.
Now, is there a way to bind the Dispose() call to garbage collector actions, because I want these objects disposed right in the moment they are no longer accessible from other code parts?
**Or maybe you could advice me some other approach? **
Generally, this seems to be the same problem as it comes, for example, in unmanaged C++ without shared pointers, where you can have a method:
SomeObject* AllocateAndConstruct();
and then you can't be sure when to dispose it, if you don't use code contracts or don't state something in the comments.
I guess the situation with disposable objects is pretty the same, but I hope there is an appropriate solution for this.
(from the question)
Now, is there a way to bind the
Dispose() call to garbage collector
actions, because I want these objects
disposed right in the moment they are
no longer accessible from other code
parts?
GC doesn't happen immediately when your object goes out of scope / reach; it is non-deterministic. By the time GC sees it, there is no point doing anything else (that isn't already handled by the finalizer), as it is too late.
The trick, then, is to know when you are done with it, and call Dispose() yourself. In many cases using achieves this. For example you could write a class that implements IDisposable and encapsulates a set of Images - and wrap your use of that encapsulating object with using. The Dispose() on the wrapper could Dispose() all the images held.
i.e.
using(var imageWrapper = GetImages()) {
foreach(var image in imageWrapper) {
...
}
// etc
} // assume imageWrapper is something you write, which disposes the child items
however, this is a bit trickier if you are displaying the data on the UI. There is no shortcut there; you will have to track when you are done with each image, or accept non-deterministic finalization.
If you want to determiniscally dispose of the objects in the collection, you should call Dispose on each:
myImages.ToList().ForEach(image => image.Dispose());
If you don't do this, and if your objects become unreachable, the GC will eventually run and release them.
Now, if you don't want to manually code the Dispose calls, you can create a wrapper class that implements IDisposable and use it through a using statement:
using (myImages.AsDisposable()) {
// ... process the images
}
This is the needed "infrastructure":
public class DisposableCollectionWrapper<D> : IDisposable
where D : IDisposable {
private readonly IEnumerable<D> _disposables;
public DisposableCollectionWrapper(IEnumerable<D> disposables) {
_disposables = disposables;
}
public void Dispose() {
if (_disposables == null) return;
foreach (var disposable in _disposables) {
disposable.Dispose();
}
}
}
public static class CollectionExtensions {
public static IDisposable AsDisposable<D>(this IEnumerable<D> self)
where D : IDisposable {
return new DisposableCollectionWrapper<D>(self);
}
}
Also notice that this is not the same as the situation you described with C++. In C++, if you don't delete your object, you have a genuine memory leak. In C#, if you don't dispose of your object, the garbage collector will eventually run and clean it up.
You should design your system in a way that you know when the resources are no longer needed. In the worst case, they'll be eventually disposed when the garbage collector gets to it, but the point of IDisposable is that you can release important resources earlier.
This "earlier" is up to you to define, for example, you can release them when the window that's using them closes, or when your unit of work finishes doing whatever operations on them. But at some point, some object should "own" these resources, and therefore should know when they're no longer needed.
You can use the 'using' block, to make sure, the IDisposable is disposed as soon the block is left. The compiler does encapsulate such blocks into try - finally statements in order to make sure, Dispose is called in any case when leaving the block.
By using a finalizer, one can make the GC call the Dispose method for those objects which where "missed" somehow. However, implementing a finalizer is more expensive and decreases the garbage collection efficiency - and possibly the overall performance of your application. So if any possible, you should try to make sure to dispose your IDisposables on your own; deterministically:
public class Context : IDisposable {
List<IDisposable> m_disposable = new List<IDisposable>();
public void AddDisposable(IDisposable disposable) {
m_disposable.Add(disposable);
}
public void Dispose() {
foreach (IDisposable disp in m_disposable)
disp.Dispose();
}
// the Context class is used that way:
static void Main(string[] args) {
using (Context context = new Context()) {
// create your images here, add each to the context
context.AddDisposable(image);
// add more objects here
} // <- leaving the scope will dispose the context
}
}
By using some clever design, the process of adding objects to the context may can get even more easier. One might give the context to the creation method or publish it via a static singleton. That way, it would be available for child method scopes as well - without having to pass a reference to the contex around. By utilizing that scheme it is even possible, to simulate an artificial destructor functionality like f.e. known from C++.
The neat method would be to create your own generic collection class that implements IDisposable. When this collection class is Disposed() ask for each element if it implements IDisposed, and if so Dispose it.
Example (look elsewhere if you don't know about the IDisposable pattern)
public class MyDisposableList<T> : List<T> : IDisposable
{
private bool disposed = false;
~MyDisposableList()
{
Dispose(false);
}
public void Dispose()
{
Dispose(true);
}
protected void Dispose(bool disposing)
{
if (!disposed)
{
foreach (T myT in this)
{
IDisposable myDisposableT = myT as IDisposable;
if (myDisposableT != null)
{
myDisposableT.Dispose();
}
myT = null;
}
this.Clear();
this.TrimExcess();
disposed = true;
}
}
...
}
usage:
using (MyDisposableList<System.Drawing.Bitmap> myList = new ...)
{
// add bitmaps to the list (bitmaps are IDisposable)
// use the elements in the list
}
The end of the using statement automatically Disposes myList, and thus all bitMaps in myList
By the way: if you loaded the bitmap from a file and you forgot to Dispose() the bitmap you don't know when you can delete that file.
You can call GC.Collect() if you really was to dispose those objects right away but to my understanding it is up to the GC to decide whether to collect the memory.
This in turn will call the Finalize() method for each object that should be released.
Note that if the collection goes out of scope the GC will eventually collect the memory used by the images.
You can also use the using construct if you use a collection that implements IDisposeable. That will guarantee that the objects will be disposed exactly when the collection goes out of scope (or nearly after the end of the scope).