Problem
C# 2008
I’ve been working on this for a long now, and I’m still not sure how to utilize finalize and dispose in code. My inquiries are as follows:
The following is a question about the source code:
Asked by ant2009
Solution #1
Here’s where you’ll find the recommended IDisposable pattern. When writing a class that uses IDisposable, you should follow one of two patterns:
When creating a sealed class that does not require unmanaged resources, you simply implement a Dispose function in the same way that you would for any other interface:
public sealed class A : IDisposable
{
public void Dispose()
{
// get rid of managed resources, call Dispose on member variables...
}
}
When creating an unsealed class, follow these steps:
public class B : IDisposable
{
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
// get rid of managed resources
}
// get rid of unmanaged resources
}
// only if you use unmanaged resources directly in B
//~B()
//{
// Dispose(false);
//}
}
You’ll see that I haven’t declared a finalizer in B; a finalizer should only be used if you have unmanaged resources to dispose of. Even if SuppressFinalize is called, the CLR treats finalizable objects differently than non-finalizable objects.
So, unless it’s absolutely necessary, you should declare a finalizer, but you should provide a hook for inheritors of your class to call your Dispose and implement a finalizer themselves if they access unmanaged resources directly:
public class C : B
{
private IntPtr m_Handle;
protected override void Dispose(bool disposing)
{
if (disposing)
{
// get rid of managed resources
}
ReleaseHandle(m_Handle);
base.Dispose(disposing);
}
~C() {
Dispose(false);
}
}
If you’re not directly using unmanaged resources (SafeHandle and friends don’t count because they declare their own finalizers), don’t implement a finalizer because the GC treats finalizable classes differently, even if you suppress the finalizer later. It’s also worth noting that, despite the fact that B lacks a finalizer, it nevertheless uses SuppressFinalize to deal with any subclasses that do.
When a class implements the IDisposable interface, it indicates that there are certain unmanaged resources that should be disposed away when the class is no longer in use. You don’t need to explicitly delete the resources because they’re wrapped within the classes. Simply invoking Dispose() or surrounding the class in a using(…) ensures that any unmanaged resources are properly disposed of.
Answered by thecoop
Solution #2
The standard pattern for implementing IDisposable is difficult to grasp. This one, I believe, is superior:
public class BetterDisposableClass : IDisposable {
public void Dispose() {
CleanUpManagedResources();
CleanUpNativeResources();
GC.SuppressFinalize(this);
}
protected virtual void CleanUpManagedResources() {
// ...
}
protected virtual void CleanUpNativeResources() {
// ...
}
~BetterDisposableClass() {
CleanUpNativeResources();
}
}
Even better, make it a rule that you must always create a wrapper class for each unmanaged resource you need to deal with:
public class NativeDisposable : IDisposable {
public void Dispose() {
CleanUpNativeResource();
GC.SuppressFinalize(this);
}
protected virtual void CleanUpNativeResource() {
// ...
}
~NativeDisposable() {
CleanUpNativeResource();
}
}
These classes should be extremely rare using SafeHandle and its variants.
Even in the presence of inheritance, the effect for disposable classes that don’t deal directly with unmanaged resources is powerful: they don’t have to worry about them anymore. They’ll be easy to apply and comprehend:
public class ManagedDisposable : IDisposable {
public virtual void Dispose() {
// dispose of managed resources
}
}
Answered by Jordão
Solution #3
Any implementation of IDisposable should follow the pattern below (IMHO). This pattern was created using information from various excellent.NET “gods,” including the.NET Framework Design Guidelines (which, for some reason, MSDN does not follow!). Krzysztof Cwalina (CLR Architect at the time) and Brad Abrams (I believe the CLR Program Manager at the time) wrote the.NET Framework Design Guidelines, as did Bill Wagner ([Effective C#] and [More Effective C#] (simply check for them on Amazon.com:
It’s worth noting that you shouldn’t use a Finalizer unless your class includes (rather than inherits) unmanaged resources. Even if a Finalizer is never called, it is guaranteed to survive for an extra collection once it is implemented in a class. It gets added to the Finalization Queue automatically (which runs on a single thread). Also, keep in mind that all code executed within a Finalizer (should you need one) must be thread-safe and exception-safe! Otherwise, bad things will happen.. (i.e. undetermined behavior and in the case of an exception, a fatal unrecoverable application crash).
The pattern I’ve devised (and for which I’ve prepared a code sample) is as follows:
#region IDisposable implementation
//TODO remember to make this class inherit from IDisposable -> $className$ : IDisposable
// Default initialization for a bool is 'false'
private bool IsDisposed { get; set; }
/// <summary>
/// Implementation of Dispose according to .NET Framework Design Guidelines.
/// </summary>
/// <remarks>Do not make this method virtual.
/// A derived class should not be able to override this method.
/// </remarks>
public void Dispose()
{
Dispose( true );
// This object will be cleaned up by the Dispose method.
// Therefore, you should call GC.SupressFinalize to
// take this object off the finalization queue
// and prevent finalization code for this object
// from executing a second time.
// Always use SuppressFinalize() in case a subclass
// of this type implements a finalizer.
GC.SuppressFinalize( this );
}
/// <summary>
/// Overloaded Implementation of Dispose.
/// </summary>
/// <param name="isDisposing"></param>
/// <remarks>
/// <para><list type="bulleted">Dispose(bool isDisposing) executes in two distinct scenarios.
/// <item>If <paramref name="isDisposing"/> equals true, the method has been called directly
/// or indirectly by a user's code. Managed and unmanaged resources
/// can be disposed.</item>
/// <item>If <paramref name="isDisposing"/> equals false, the method has been called by the
/// runtime from inside the finalizer and you should not reference
/// other objects. Only unmanaged resources can be disposed.</item></list></para>
/// </remarks>
protected virtual void Dispose( bool isDisposing )
{
// TODO If you need thread safety, use a lock around these
// operations, as well as in your methods that use the resource.
try
{
if( !this.IsDisposed )
{
if( isDisposing )
{
// TODO Release all managed resources here
$end$
}
// TODO Release all unmanaged resources here
// TODO explicitly set root references to null to expressly tell the GarbageCollector
// that the resources have been disposed of and its ok to release the memory allocated for them.
}
}
finally
{
// explicitly call the base class Dispose implementation
base.Dispose( isDisposing );
this.IsDisposed = true;
}
}
//TODO Uncomment this code if this class will contain members which are UNmanaged
//
///// <summary>Finalizer for $className$</summary>
///// <remarks>This finalizer will run only if the Dispose method does not get called.
///// It gives your base class the opportunity to finalize.
///// DO NOT provide finalizers in types derived from this class.
///// All code executed within a Finalizer MUST be thread-safe!</remarks>
// ~$className$()
// {
// Dispose( false );
// }
#endregion IDisposable implementation
The code for implementing IDisposable in a derived class can be found here. It’s worth noting that in the definition of the derived class, you don’t have to explicitly mention inheritance from IDisposable.
public DerivedClass : BaseClass, IDisposable (remove the IDisposable because it is inherited from BaseClass)
protected override void Dispose( bool isDisposing )
{
try
{
if ( !this.IsDisposed )
{
if ( isDisposing )
{
// Release all managed resources here
}
}
}
finally
{
// explicitly call the base class Dispose implementation
base.Dispose( isDisposing );
}
}
This approach is documented on my blog: How to Properly Implement the Dispose Pattern.
Answered by 6 revs
Solution #4
I concur with pm100 (and should have explicitly said this in my earlier post).
If you don’t need IDisposable, don’t implement it in a class. To be more exact, there are approximately five situations where you would need/should use IDisposable:
Working with COM objects and having to utilize Marshal is a preferred alternative. To use the System, call ReleaseComObject(). Runtime. InteropServices. The SafeHandle class is a wrapper for the SafeHandle class.
http://blogs.msdn.com/bclteam/archive/2005/03/16/396900.aspx The BCL (Base Class Library Team) has a decent blog article on it.
One thing to keep in mind while working with WCF and cleaning up resources is that you should almost never use the ‘using’ block. There are numerous blog posts and MSDN articles explaining why this is a horrible idea. I have also posted about it here – Don’t use ‘using()’ with a WCF proxy
Answered by 4 revs, 2 users 88%
Solution #5
Instead than using IDisposable, lambdas are used.
I’ve never been a fan of the entire using/disposable concept. The issue is that it requires the caller to do the following:
My new preferred method is to use a factory method and a lambda instead
Consider the following scenario: I want to do something with a SqlConnection (something that should be wrapped in a using). Traditionally, you would.
using (Var conn = Factory.MakeConnection())
{
conn.Query(....);
}
New way
Factory.DoWithConnection((conn)=>
{
conn.Query(...);
}
The caller might simply not utilize the using syntax in the first example. The user has no choice in the second scenario. The caller must use DoWithConnection to build a SqlConnection object because there is no mechanism to do so.
This is how DoWithConnection appears.
void DoWithConnection(Action<SqlConnection> action)
{
using (var conn = MakeConnection())
{
action(conn);
}
}
MakeConnection is now closed to the public.
Answered by pm100
Post is based on https://stackoverflow.com/questions/898828/use-of-finalize-dispose-method-in-c-sharp