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How to properly dispose locally created object in another method?

So I have a class which implements IDisposable, and I have several methods (in another class) which follow the pattern below:
public void SomeMethod()
{
DisposableObject disposableObject = new DisposableObject();
// Do some stuff with the object
SomeOtherMethod(disposableObject);
disposableObject.Dispose();
}
While all of these methods do different things, they all call SomeOtherMethod at the end, which does a few more things with the disposable object before it's no longer needed.
When I move disposableObject.Dispose(); into SomeOtherMethod, Visual Studio gives me a message saying:
"Use recommended dispose pattern to ensure that object created by 'new DisposableObject()' is disposed on all paths: using statement/declaration or try/finally"
This message appears regardless of whether or not I pass the disposable object to SomeOtherMethod using the ref keyword.
My question is, will that object be disposed as long as SomeOtherMethod calls Dispose() on it? I'm assuming it will, and Visual Studio continues to send the message simply because it isn't "aware" of what's happening to that object in subsequent methods, but I'd love to get some confirmation on that!

It may be disposed or may be not, depends on the fact whether the execution will reach the Dispose invocation or not and that's because an exception can be thrown before the Dispose is called. Using try finally construction explicitly or implicitly by using keyword ensures that it will be called for any scenario and that's why VS gives you the warning.

will that object be disposed
Sorry, but that’s a meaningless question. The CLR does not keep track of whether an object has had its “dispose” method called or not (see Will the Garbage Collector call IDisposable.Dispose for me? )
As a general rule, it is always much nicer (readable/ maintainable / less-bug-prone / etc) that a method that creates an issue should also be the one that cleans up after itself. As you’ve just found, this pattern also allows automated checking by the compiler - and again, it is also a good rule to ensure that your code compiles cleanly without errors OR WARNINGS.
In this case, the warning is giving you a couple of ways to implement this cleanly; personally, I would prefer the “using” clause (so avoiding having to have an explicit call to “dispose”) like :
public void SomeMethod()
{
using (DisposableObject disposableObject = new DisposableObject() )
{
// Do some stuff with the object
SomeOtherMethod(disposableObject);
}
}

No matter where one call the Dispose(), it is called.
Not using the language keyword using for the disposable pattern, therefore moving the dispose in another method, is an anti-pattern, therefore it is a bad practice and a source of potential problems.
You can only remove the warning by adding the warning number in the project build settings.
The method Dispose() doesn't destroy the object.
The dispose pattern is only for freeing unmanaged resources like windows handle and shared memories.
After a call to Dispose() you still have the object and so the reference to the object that remains referenced in the managed memory.
Dispose() is made to be called once time at the end of object usage and no more.
The compiler send you a warning because you break the standard behavior of the pattern usage that is to use the using keyword.
And breaking standards can be source of problems.
The using of disposable objects standard is made to avoid bugs by letting the compiler generates the try { ... } finally { Dispose() } block to be sure that Dispose() is correctly called in the right place to avoid mistakes.
So avoid calling the Dispose() directly.
Unless you are sure of what you do, prefer using:
public void SomeMethod()
{
using ( DisposableObject disposableObject = new DisposableObject() )
{
// Do some stuff with the object
SomeOtherMethod(disposableObject);
}
}
And your code may be robust.

Should IDisposable.Dispose() implementations be idempotent?

The Microsoft.NET framework provides the IDisposable interface which requires an implementation of void Dispose() method. Its purpose is to enable manual, or scope-based releasing of expensive resources an IDisposable implementation may have allocated. Examples include database collections, streams and handles.
My question is, should the implementation of the Dispose() method be idempotent - when called more than once on the same instance, the instance to be 'disposed of' only once, and subsequent calls not to throw exceptions. In Java, most of the objects that have similar behavior (again streams and database connections come to my mind as examples) are idempotent for their close() operation, which happens to be the analogue for the Dispose() method.
However, my personal experience with .NET (and Windows Forms in particular), shows that not all implementations (that are part of the .NET framework itself) are idempotent, so that subsequent calls to these throw an ObjectDisposedException. This really confuses me on how a disposable object's implementation should be approached. Is there a common answer for the scenario, or is it dependent on the concrete context of the object and its usage?

should the implementation of the Dispose() method be idempotent
Yes, it should. There is no telling how many times it will be called.
From Implementing a Dispose Method on MSDN:
a Dispose method should be callable multiple times without throwing an exception.
An object with a good implementation of IDispose will have a boolean field flag indicating if it has been disposed of already and on subsequent calls do nothing (as it was already disposed).

Yes, also make sure the other methods of the class respond correctly when they are called when the object has already been disposed.
public void SomeMethod()
{
if(_disposed)
{
throw new ObjectDisposedException();
}
else
{
// ...
}
}

From MSDN:
Allow a Dispose method to be called more than once without throwing an exception. The method should do nothing after the first call.

Personally - Yes - I always make Dispose() idempotent.
During the usual life-cyle of an object in a given application it may not be necessary - the life-cyle from creation to disposal may be deterministic and well known.
However, equally, in some applications it might not be so clear.
For example, in a decorator scenario: I may have a disposable object A, decorated by another disposable object B. I may want to explicitly dispose A, and yet Dispose on B may also dispose the instance it wraps (think: streams).
Given it is relatively easy to make Dispose idempotent (ie if already disposed, do nothing), it seems silly not to.

What is this IDisposable doing for me?

I am working on a "learning program" and using the Code Rush refactoring tool with my learning. With the latest update of Code Rush it has been recommending implementing IDisposable to my programs. I know what MSDN says about IDisposable and I have a real basic understanding of what it does but because I don't know all the implications of implementing it I have been ignoring the recommendation. Today I decided to learn more about it and went along with the recommendation.
This is what it added to my program.
class Program : IDisposable
{
static Service _proxy;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
if (_proxy != null)
{
_proxy.Dispose();
_proxy = null;
}
}
~Program()
{
Dispose(false);
}
So my questions is this. Does that do everything I need to do to get the advantage of IDisposable or do I need to do something in code to make it work? I put a break points on that and never reached it through the debugger so either it was not needed or I am not using it the way it was intended. Can someone please shed some light on what this is doing for me or how I should use it so it does do something for me?

In this case, CodeRush is suggesting you implement IDisposable because your class encapsulates an IDisposable resource (it's seeing _proxy, though that's not entirely a good thing since it's static). Code Rush thinks that there is a type that you're using which should be explicitly cleaned up, but you're not providing a way to do it via your class.
That being said, IDisposable is tricky - and this is one case where the generated code is not really a good implementation (even if _proxy were an instance variable). I would recommend not using the destructor in this case. It will cause performance issues in the GC, and in this case, doesn't help with the safety, as the encapsulated resource should handle that the case where you forget to call Dispose() for you. For details, see my series on IDisposable, and, in particular, encapsulating an IDisposable class.
In addition, this class shouldn't implement IDisposable (unless there is some other reason to do so) given the code above, as the _proxy resource is static. Disposing a static resource from an instance is likely to cause problems, at least in a general case. (In this case, it's obviously not problematic, but it's not a good practice...) Typically, a static variable has a very different lifetime than an instance member, so automatically disposing of it would be inappropriate.

In a properly-written program, at any given time, for every object that could possibly have a meaningful implementation of IDisposable, there will be some entity that is responsible for ensuring that IDisposable.Dispose will get called on that object sometime between the last "real use" of that instance and its ultimate abandonment. In general, if an object Foo is going to hold references to objects which implement IDisposable, at least one of the following scenarios should apply:
Some other object will also hold the reference for at least as long as Foo needs it, and will take care of calling Dispose on it, so Foo should let the other object take care of the Dispose.
The object holding the reference will be the last thing to use the IDisposable object in question; if Foo doesn't call Dispose, nothing else will. In that scenario, Foo must ensure that that other object's Dispose method gets called once it (Foo) is no longer needed, and before it is abandoned. The most idiomatic way to handle this is for Foo to implement IDisposable.Dispose, and for its Dispose method to call Dispose on the IDisposable objects to which it holds the last useful references.
There are some scenarios where a class designer might not know whether its class is going to hold the last useful reference to an IDisposable object. In some cases, this issue may be resolved by having a class constructor specify whether a IDisposable passed to the constructor is being "lent" or "given". Other cases may require the use of reference-counting wrappers or other complex techniques.

How to perform an operation before object is disposed?

Working with C#. I have an abstract class that I use to read/write settings to an xml file. When the class is no longer needed I want to perform one last write operation to the xml file before the class gets disposed. I tried putting this code in a destructor method ~myClass() {} but it throws an exception saying that the safe handle is closed. I am guessing this means that the class is already disposed or partially disposed. So if the destructor is not the correct place to do this where is the correct place? Do I need to implement IDisposable or something?

There is no such thing as a destructors in C#. Please refer to this question's accepted answer from Jon Skeet who explains and provide a good article on the topic.
Sample use of a C# Destructor
Besides, perhaps should you consider to implement the IDisposable interface in your class so that you could perform your manoeuvre.

There are many threads on finalizers on SO just read a few of them.
The basic point is that you should never rely on finalizers since their execution order is undefined or might not run at all. You should use IDisposablefor any managed cleanup(your case) and SafeHandles/CriticalFinalization for native resources.

It sounds like today you are attempting to write out to the settings file in your object's finalizer using a SafeHandle field. This is not the right approach.
Once the object hits the CLR finalizer thread, all bets are off about other managed resources the object can see. It's very legal and possible for the SafeHandle field to already be finalized and hence invalid by the time the containing class`s finalizer runs.
The standard way to work with a scenario like this is to implement IDisposable and use the Dispose method (which is intended to be called by user code) to properly dispose of managed resources such as the file.
For example:
abstract class MyClass : IDisposable {
private SafeFileHandle _handle;
public void Dispose() {
WriteTheFile();
_handle.Dispose();
}
}

If you need to have your finalizer give you a chance to write some stuff before the file is closed, you need to ensure that a strong reference to the file will outlive your object. One way to do this would be to store a strong reference to the file in a static field. When your object's finalizer runs, you can write the data, close the file, and null out the static field. Note that if your finalizer fails to null out the field, for whatever reason, the file may be kept open indefinitely.

Consider a "disposable" keyword in C#

What are your opinions on how disposable objects are implemented in .Net? And how do you solve the repetitiveness of implementing IDisposable classes?
I feel that IDisposable types are not the first-class citizens that they should've been. Too much is left to the mercy of the developer.
Specifically, I wonder if there should'nt have been better support in the languages and tools to make sure that disposable things are both implemented correctly and properly disposed of.
In C# for instance, what if my class that needs to implement the disposable semantics could be declared like this:
public class disposable MyDisposableThing
{
~MyDisposableThing()
{
// Dispose managed resources
}
}
The compiler could in this case easily generate an implementation of the IDisposable interface. The destructor ~MyDisposableThing could be transformed into the actual Dispose method that should release managed resources.
The intermediate C# code would look like this:
public class MyDisposableThing : IDisposable
{
private void MyDisposableThingDestructor()
{
// Dispose my managed resources
}
~MyDisposableThing()
{
DisposeMe(false);
}
public void Dispose()
{
DisposeMe(true);
GC.SuppressFinalize(this);
}
private bool _disposed;
private void DisposeMe(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
// Call the userdefined "destructor"
MyDisposableThingDestructor();
}
}
_disposed = true;
}
}
This would make for much cleaner code, less boilerplate disposing code, and a consistent way of disposing managed resources. Implementing IDisposable by hand would still be supported for edge cases and unmanaged resources.
Ensuring that instances are properly disposed is another challenge. Consider the following code:
private string ReadFile(string filename)
{
var reader = new StreamReader();
return reader.ReadToEnd(filename);
}
The reader variable never outlives the scope of the method but would have to wait for the GC to dispose it. In this case, the compiler could raise an error that the StreamReader object was not explicitly disposed. This error would prompt the developer to wrap it in a using statement:
private string ReadFile(string filename)
{
using (var reader = new StreamReader())
{
return reader.ReadToEnd(filename);
}
}

An oft-stated principle is that "design patterns are needed to address language deficiencies". This is an example of that principle. We need the disposable pattern because the language doesn't give it to you.
I agree that disposability could have been elevated out of the "pattern" world and into the C# language proper, as we did with, say, property getters and setters (which are standardizations of the pattern of having getter and setter methods), or events (which standardize the idea of storing a delegate and calling it when something interesting happens.)
But language design is expensive and there is a finite amount of effort that can be applied to it. Thus we try to find the most useful, compelling patterns to put into the language proper. And we try to find a way that does so in a way that is not merely convenient, but actually adds more expressive power to the language. LINQ, for example, moves the concepts of filtering, projecting, joining, grouping and ordering data into the language proper, which adds a lot of expressive power to the language.
Though this is certainly a good idea, I don't think it meets the bar. It would be a nice convenience, I agree, but it doesn't enable any really rich new scenarios.

In addition to the other answers, there is the problem of how much should this implement and what should people expect from it? Say I declared my class like this:
public disposable class MyClass
{
readonly AnotherDisposableObject resource = new AnotherDisposableObject();
~MyClass()
{
this.resource.Dispose();
}
public void DoStuff()
{
this.resource.SomeMethod();
}
}
Then what would you expect to happen if a caller called DoStuff after the instance had been disposed? Should the compiler automatically insert something like
if (this.disposed) throw new ObjectDisposedException();
at the start of every method because you have declared the class as disposable?
If so then what about cases where methods are explicitly allowed to be called after an object is disposed (e.g. MemoryStream.GetBuffer)? Would you have to introduce a new keyword that indicated this to the compiler, e.g. public useafterdispose void ...?
If not then how do you explain to people that the new keyword implements some of the boiler-plate code for you, but that they still need to write code to check whether the object is disposed in each method? Moreover, how can they even check this, because all the state information about whether the object has been disposed is auto-generated! Now they need to track their own flag in the ~MyClass method which undoes half the work the compiler should be doing for you.
I think as a specific language pattern there are too many holes in the concept, and it only attempts to solve one specific problem. Now what could solve this entire class of problem in a general-purpose fashion is mixins (i.e. a Disposable mixin) and this language feature would be generally reusable for different concepts (e.g. Equatable mixin, Comparable mixin, etc.). That's where my money would go.

Personally, I consider the support for IDisposable to be quite decent in the current version of .NET. The presence of the using keyword pretty much makes it into a first-class construct for me.
I do admit there is a certain amount of boilerplate code involved, but not enough to warrant a new language features. (Auto-implemented properties was a good example of a feature that was begging to be introduced.) You've missed out an important point in your post that this "boilerplate" code is not always what you need. Mainly, you need to dispose unmanaged resources outside of the if (disposing) block.
Of course, the destructor (~MyDisposableThing) and parameterless Dispose() method are genuinely boilerplate and could be eliminated by the user of a language keyword, as you suggest - but again I'm not sure the introduction of an actual new keyword is all that necessary for a few lines of code.
I certainly see the point you are making here, and do sympathise with it to some degree. (I'm sure no coder would complain if your suggestion becamse part of the language specification.) However, it's not likely to convince the .NET development team when there are a rather limited number of lines of code anyway, some of which are arguably fairly context-specific (and thus not boilerplate).

I completely agree that IDisposable needs better language suppprt. Here's my variant of it from a while ago. The details are probably wrong, but C++/CLI serves as a pretty good model for this. Unfortunately it confuses the hell out of C# programmers when I show them examples in C++/CLI. But it already does "the right thing" in terms of implementation; we would just need a new syntax in C#.
Even the simplest Windows Forms application has a Dispose method in it, which is generated by a wizard and is fragile in the face of inexpert changes. The idea of composing components together such that one component can "own" several others is so fundamental that IDisposable is practically unavoidable, and unfortunately it seems to take several pages of most books to explain how to implement it correctly.
The existing using statement takes care of the client side. Where we need more language support is on the implementation side.
Some of the fields of a class are references to things that the class "owns", and some not owned. So we have to be able to mark a field as owned.
Also, it would be a very bad idea to automatically generate a finalizer. Most often, a class will own other objects that implement IDisposable. Not all classes are thread safe, nor should they need to be. If they are called from a finalizer, that happens on another thread, forcing them to be thread safe. This is probably the one area around IDisposable that causes the most confusion - a lot of people read the books and come away with the mistaken impression that you have to write a finalizer on an object that supports IDisposable.

I realize this is an old thread but there is something that has been overlooked.
Dispose pattern in both C# and Java break the fundamental reason for not having a deterministic destructor.
MyObject A = new MyObject()
MyObject B = A;
A.Dispose();
What is the state of B now? What if the owner of B didn't really want it disposed. You now have the same issue in C++ where you have to keep track of all the references of objects you are holding on to.
IDisposable is only truly valid within the context of using() and ensuring resource cleanup if an exception occurs.
There are design patterns to do this but it isn't IDisposable
#Peter Yes I am arguing that the Dipsosable pattern has a fault. When implemented the Disposable pattern isn't normally meant to just dispose OS resources with the idea of being able to continue using the object that was disposed. By using the Disposable pattern outside of a try{} finally{} in Java or using() in .NET you break one of the reasons of having a GC. I am not saying memory will leak. I am saying you can now have other parts of the code that have a reference to an Object that has been disposed. Now the onus is back on the developer to check if an object has been disposed before each call, or at the very least catch a ObjectDisposedException.
Lets look at a silly example:
FileStream stream = new FileStream (#"c:\mylog.txt");
logger.setStream (stream);
Who is supposed to invoke .Dispose()? It may not be obvious that the logger is now aquiring ownership of the file stream. Let's say the stream was created somewhere else outside of the developer knowing it will be set as the logging stream.
if we were to add one line, we would break the logger
using (FileStream stream = new FileStream (#"c:\mylog.txt"))
{ logger.setStream (stream); }
or
FileStream stream = new FileStream (#"c:\mylog.txt");
logger.setStream (stream);
stream.Dispose();
The Disposable pattern does not reference count for resources. The developer now has to be conscious of who owns the object and who is responsible for cleaning it up. The real problem is that when Dispose() is invoked the normal behavior is to invalidate the whole object preventing it from being used.

IMHO, the .net languages have a major shortcoming in their handling of iDisposable, which is that there is no nice way of handling initializers that throw exceptions. Unless one 'leaks' a copy of the object under construction or the disposable objects therein, there's no way to clean up any iDisposable objects which were created (either in an initializer, or a base-level constructor) before an initializer throws.
Two features I would like to see toward that end:
A class declaration that would cause a particular method to be invoked if an exception throws out of its constructor.
A field declaration which would indicate that the field should have .Dispose called upon it if some special private method or keyword is used on the object.
BTW, I would also like to see a declaration available for structure methods which would indicate that the method alters the underlying structure. Use of such methods would be forbidden on structure rvalues, and use of such methods on structure properties would generate a read-modify-write sequence.

Okay you need to understand the difference between managed and unmanaged memory.
Put simply, c++ style destructors wouldn't work in the managed world of c# because there's no guarantee when the object gets garbage collected, hence you would never know when the destructor would get called, which would make things very unpredictable.
As opposed to c++, when destructors get called as soon as the class goes out of scope, so you can guarantee when it gets called.
This is the reason why c# can't have destructors.