This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Will the Garbage Collector call IDisposable.Dispose for me?
I have a Class which has some unmanaged resources. My class implements the IDisposable interface and releases the unmanaged resources in the Dispose() method. Do I have to call the Dispose() method or will it be automatically called somehow? Will the Garbage Collector call it?
Dispose() will not be called automatically. If there is a finalizer it will be called automatically. Implementing IDisposable provides a way for users of your class to release resources early, instead of waiting for the garbage collector.
The preferable way for a client is to use the using statement which handles automatic calling of Dispose() even if there are exceptions.
A proper implementation of IDisposable is:
class MyClass : IDisposable
{
private bool disposed = false;
void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if(!disposed)
{
if(disposing)
{
// Manual release of managed resources.
}
// Release unmanaged resources.
disposed = true;
}
}
~MyClass() { Dispose(false); }
}
If the user of the class calls Dispose() the cleanup takes place directly. If the object is catched by the garbage collector, it calls Dispose(false) to do the cleanup. Please note that when called from the finalizer (the ~MyClass method) managed references may be invalid, so only unmanaged resources can be released.
If you instantiate your object in a using statement, Dispose() is called for you when code exits the using block
using(var myObject = new MyDisposableObject())
{
blah();
} // Dispose() is called here (or whenever the code exits the block)
If you don't use using, then it's up to you (the calling code) to dispose of your object by explicitely calling Dispose().
Also, you (the implementor of MyObject) can add support for a finalizer in case your caller doesn't call Dispose(). More info here.
You will have to call this method manually, maybe (assuming that "MyClass" implements "IDisposable") in a construct like
using(var myclass = new MyClass())
{
// do something with myclass
}
// now 'myclass'is Disposed
In C# 8.0, you can write as below statement:
using var myclass=new MyClass();
and the "myclass" will be disposed automatically at the end of the scope.
The advantage of the using statement (compared to calling Dispose() explicitly) is that Dispose() is called no matter how you exit this block: by running past the end, encountering a return statement or having an exception thrown.
To make sure the resources are correctly disposed, you need to both implement IDisposable and call Dispose in the destructor(finalizer).
class Foo : IDisposable
{
private bool m_disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~Foo()
{
Dispose(false);
}
protected void Dispose(bool disposing)
{
if (!m_disposed)
{
if (disposing)
{
//release managed resources
}
//release unmanaged resources
m_disposed = true;
}
}
}
Related
This question already has answers here:
Proper use of the IDisposable interface
(20 answers)
Closed 3 years ago.
I am trying to work out exactly what I need to do to dispose of a property in C# when using IDisposable. I can see the template, but I am not sure about actually disposing of objects.
I am working with the example given on this site:
https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/implementing-dispose
I have added 3 properties:
privInt: Private value type. Would I dispose of this as it could be saved on the heap so may require GC? If I would then how, cannot set to null or call dispose? If not then I assume it has to be left to GC - but is it not the point of Dispose to free resources?
NonIDisClassInstance - Do I set to null? Is that enough
Can anyone comment on my implementation below and advise on what is correct/wrong.
IDisClass - Just call dispose
class BaseClass : IDisposable
{
// Flag: Has Dispose already been called?
bool disposed = false;
// Public implementation of Dispose pattern callable by consumers.
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
//Private value type
private int privInt;
//Private class that does not implement IDisposable
Private NonIDisClass NonIDisClassInstance;
//Private class that does implement IDisposable
Private IDisClass IDisClassInstance;
// Protected implementation of Dispose pattern.
protected virtual void Dispose(bool disposing)
{
if (disposed)
return;
if (disposing) {
// Free any other managed objects here.
//
}
// Free any unmanaged objects here.
DisposeOfThis = ????;
NonIDisClassInstance = null;
IDisClassInstance.Dispose();
disposed = true;
}
~BaseClass()
{
Dispose(false);
}
}
You only need GC.SuppressFinalize(this); and a destructor if you are working with unmanaged memory. If not you can safely omit this.
In your Dispose implementation call this.IDisClassInstance?.Dispose();, that is all you need.
Your code can be condensed down to this.
class BaseClass : System.IDisposable
{
public virtual void Dispose()
{
// never throw an exception from Dispose so prevent an NRE by using ?.
this.IDisClassInstance?.Dispose();
}
//Private class that does not implement IDisposable
private object NonIDisClassInstance;
//Private class that does implement IDisposable
private IDisposable IDisClassInstance;
}
Do keep in mind that using Dispose is not necessarily about freeing up memory, it is about cleaning up / freeing up unmanaged resources which might also include memory. Things like open file streams or database connections or network connections.
Note that your derived types can override Dispose but those overriden methods should include a call to base.Dispose(); so the managed resources of the base class are released.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Will the Garbage Collector call IDisposable.Dispose for me?
I have a Class which has some unmanaged resources. My class implements the IDisposable interface and releases the unmanaged resources in the Dispose() method. Do I have to call the Dispose() method or will it be automatically called somehow? Will the Garbage Collector call it?
Dispose() will not be called automatically. If there is a finalizer it will be called automatically. Implementing IDisposable provides a way for users of your class to release resources early, instead of waiting for the garbage collector.
The preferable way for a client is to use the using statement which handles automatic calling of Dispose() even if there are exceptions.
A proper implementation of IDisposable is:
class MyClass : IDisposable
{
private bool disposed = false;
void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if(!disposed)
{
if(disposing)
{
// Manual release of managed resources.
}
// Release unmanaged resources.
disposed = true;
}
}
~MyClass() { Dispose(false); }
}
If the user of the class calls Dispose() the cleanup takes place directly. If the object is catched by the garbage collector, it calls Dispose(false) to do the cleanup. Please note that when called from the finalizer (the ~MyClass method) managed references may be invalid, so only unmanaged resources can be released.
If you instantiate your object in a using statement, Dispose() is called for you when code exits the using block
using(var myObject = new MyDisposableObject())
{
blah();
} // Dispose() is called here (or whenever the code exits the block)
If you don't use using, then it's up to you (the calling code) to dispose of your object by explicitely calling Dispose().
Also, you (the implementor of MyObject) can add support for a finalizer in case your caller doesn't call Dispose(). More info here.
You will have to call this method manually, maybe (assuming that "MyClass" implements "IDisposable") in a construct like
using(var myclass = new MyClass())
{
// do something with myclass
}
// now 'myclass'is Disposed
In C# 8.0, you can write as below statement:
using var myclass=new MyClass();
and the "myclass" will be disposed automatically at the end of the scope.
The advantage of the using statement (compared to calling Dispose() explicitly) is that Dispose() is called no matter how you exit this block: by running past the end, encountering a return statement or having an exception thrown.
To make sure the resources are correctly disposed, you need to both implement IDisposable and call Dispose in the destructor(finalizer).
class Foo : IDisposable
{
private bool m_disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~Foo()
{
Dispose(false);
}
protected void Dispose(bool disposing)
{
if (!m_disposed)
{
if (disposing)
{
//release managed resources
}
//release unmanaged resources
m_disposed = true;
}
}
}
Here is a typical IDispose implementation. What I don't understand is the destructor?
If the user of your class forgets to call Dispose, wouldn't you have a resource leak since the destructor will not call r1.Dispose()?
public class DisposableObject : IDisposable
{
private bool disposed;
private UnmanagedResource r1;
public DisposableObject()
{
r1 = new UnmanagedResource();
}
~DisposableObject()
{
this.Dispose(false);
}
public void Dispose()
{
this.Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
// clean up managed resources
//call dispose on your member objects
r1.Dispose();
}
// clean up unmanaged resources
this.disposed = true;
}
}
public void SomeMethod()
{
if (this.disposed)
{
throw new ObjectDisposedException(this.GetType().FullName);
}
}
}
No - the GC will call the destructor once all references to the object are gone (this is not deterministic, however).
If r1 is truly a native resource (which it doesn't look like it in your example), it should not be disposed of inside the if(disposing) block but after it. Pay particular attention to:
if (disposing)
{
// free managed resources
if (managedResource != null)
{
managedResource.Dispose();
managedResource = null;
}
}
// free native resources if there are any.
if (nativeResource != IntPtr.Zero)
{
Marshal.FreeHGlobal(nativeResource);
nativeResource = IntPtr.Zero;
}
From Implement IDisposable Correctly - MSDN
If r1 is a managed resource with its own implementation of IDisposable, assuming it is implemented properly, any native resources will be cleaned up properly in its finalizer (which is why you don't need to worry about it in your own).
The reason for the destructor (finalizer) to call Dispose is because Garbage Collector calls it before it collects an object, guaranteeing that at least at some point the UnmanagedResource will be freed.
By using using and try...finally you can enforce the resource to be disposed as soon as they are not needed
http://msdn.microsoft.com/en-us/library/system.object.finalize.aspx
If you really want to, you can add a finalizer:
~DisposeImplementation()
{
Dispose(false);
}
But it should only be used as a true last resort, not something to rely on directly.
In .Net, we have a feature called Garbage Collection. Garbage Collection finalizes all Objects that are not referenced (any more). Your Destructor / finalizer then calls Dispose().
If your user forgets to remove those references, you will end up with sort-of a leak.
But that's what using is for : avoid memory blockage by defining your disposables only in the scope of requirement.
The pattern exists because the garbage collector does not guarantee the order that managed objects will be garbage collected. So in the finalizer you are not guaranteed that the r1 reference is still valid.
Your r1 reference has a class name of UnmanagedResource but it is clearly a managaged type. For a real unmanned resource you would only have an IntPtr or some other token. To ensure that r1 does non like it's resource it should implement the same Dispose pattern and free it's unmanaged resource outside of the if (disposing) check.
This question already has answers here:
Closed 11 years ago.
Possible Duplicate:
Will the Garbage Collector call IDisposable.Dispose for me?
I have a Class which has some unmanaged resources. My class implements the IDisposable interface and releases the unmanaged resources in the Dispose() method. Do I have to call the Dispose() method or will it be automatically called somehow? Will the Garbage Collector call it?
Dispose() will not be called automatically. If there is a finalizer it will be called automatically. Implementing IDisposable provides a way for users of your class to release resources early, instead of waiting for the garbage collector.
The preferable way for a client is to use the using statement which handles automatic calling of Dispose() even if there are exceptions.
A proper implementation of IDisposable is:
class MyClass : IDisposable
{
private bool disposed = false;
void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if(!disposed)
{
if(disposing)
{
// Manual release of managed resources.
}
// Release unmanaged resources.
disposed = true;
}
}
~MyClass() { Dispose(false); }
}
If the user of the class calls Dispose() the cleanup takes place directly. If the object is catched by the garbage collector, it calls Dispose(false) to do the cleanup. Please note that when called from the finalizer (the ~MyClass method) managed references may be invalid, so only unmanaged resources can be released.
If you instantiate your object in a using statement, Dispose() is called for you when code exits the using block
using(var myObject = new MyDisposableObject())
{
blah();
} // Dispose() is called here (or whenever the code exits the block)
If you don't use using, then it's up to you (the calling code) to dispose of your object by explicitely calling Dispose().
Also, you (the implementor of MyObject) can add support for a finalizer in case your caller doesn't call Dispose(). More info here.
You will have to call this method manually, maybe (assuming that "MyClass" implements "IDisposable") in a construct like
using(var myclass = new MyClass())
{
// do something with myclass
}
// now 'myclass'is Disposed
In C# 8.0, you can write as below statement:
using var myclass=new MyClass();
and the "myclass" will be disposed automatically at the end of the scope.
The advantage of the using statement (compared to calling Dispose() explicitly) is that Dispose() is called no matter how you exit this block: by running past the end, encountering a return statement or having an exception thrown.
To make sure the resources are correctly disposed, you need to both implement IDisposable and call Dispose in the destructor(finalizer).
class Foo : IDisposable
{
private bool m_disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~Foo()
{
Dispose(false);
}
protected void Dispose(bool disposing)
{
if (!m_disposed)
{
if (disposing)
{
//release managed resources
}
//release unmanaged resources
m_disposed = true;
}
}
}
I am writing an excel class and i want to release this unmanaged object automatically.
I'm using IDisposable pattern and write Dispose methods.
Example ;
class MSExcel : IDisposable
{
ApplicationClass excel;
bool disposed;
public MSExcel()
{
disposed = false;
excel = new ApplicationClass();
}
public void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
}
excel.Quit();
disposed = true;
}
}
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
~MSExcel()
{
Dispose(false);
}
}
But i have classical error on exc.Quit().
"COM object that has been separated from its underlying RCW".
Have any my mistake in code?
As explained in my answer to your other related question here, you should not be taking actions on reference types from within your finalizer. You enforce this by making use of the bool disposing parameter of your Disposed(bool) method, as you have done. You pass in true, when Disposed(bool) is called explicitly from the void Dispose() method, and pass in false when called from your finalizer, which you have also done.
However, you also need to protect your call to excel.Quit() so that it is not called when Disposed(bool) is called via the finalizer. That is, you should only call excel.Quit() when the bool disposing argument is true.
Therefore, the code for your Disposed(bool) method should look as follows:
public void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
excel.Quit();
}
disposed = true;
}
}
Once done, you could make use of your "MSExcel" class as follows:
using (MSExcel msExcel = new MSExcel)
{
// The code calling your 'MSExcel' object goes here.
}
By doing it this way, when your code gets to the closing bracket, "}", of your using statement block, the Dispose method on your 'MSExcel' class will be called automatically, ensuring that excel.Quit() is called deterministically, and not from a finalizer.
Hope this helps...
Mike