Is correct that a public method calls the Dispose of IDisposable in the same class?
E.g.
public class Worker : IDisposable
{
public void Close()
{
SendCloseCommand();
Dispose();
}
public void Dispose()
{
////other resources release
}
private void SendCloseCommand()
{
}
}
Another thing about disposable pattern:
If the Close should be always called, is better that is called from the Dispose method or not?
If not, I should put the usage of the Worker class in a try/catch/finally everywhere, to call the Close. Right?
The correct design should instead be?
public class Worker : IDisposable
{
public void Close()
{
SendCloseCommand();
}
public void Dispose()
{
Close();
////other resources release
}
private void SendCloseCommand()
{
////other stuff
}
}
If you look at Microsoft implementation for StreamReader, Dispose gets called from Close,
public override void Close()
{
Dispose(true);
}
and also the implementation for Dispose closes the stream as well by calling Close of base Stream.
protected override void Dispose(bool disposing)
{
// Dispose of our resources if this StreamReader is closable.
// Note that Console.In should be left open.
try {
// Note that Stream.Close() can potentially throw here. So we need to
// ensure cleaning up internal resources, inside the finally block.
if (!LeaveOpen && disposing && (stream != null))
stream.Close();
}
finally {
if (!LeaveOpen && (stream != null)) {
stream = null;
encoding = null;
decoder = null;
byteBuffer = null;
charBuffer = null;
charPos = 0;
charLen = 0;
base.Dispose(disposing);
}
}
}
In your class implementation, I would call the Dispose from your Close method as you are doing in your first code snippet. In Dispose, I would check for Worker status, if it is not closed then close it using SendCloseCommand, and then release resources.
public void Dispose()
{
if(this.Status != Closed) // check if it is not already closed
{
SendCloseCommand();
}
////other resources release
}
This will ensure your resources disposal, even if your class is used with using statement, or if any one calls Close manually.
Just remember to check status of your Worker object, before issuing Close Command.
Microsoft has some suggestions about having a Close method on a class implementing IDisposable. It is part of the Dispose Pattern guidelines:
CONSIDER providing method Close(), in addition to the Dispose(), if close is standard terminology in the area.
When doing so, it is important that you make the Close implementation identical to Dispose and consider implementing the IDisposable.Dispose method explicitly.
public class Stream : IDisposable {
IDisposable.Dispose(){
Close();
}
public void Close(){
Dispose(true);
GC.SuppressFinalize(this);
}
}
So Microsofts suggestion is to hide Dispose and let it call Close to do the actual cleanup. Also, remember the guideline about multiple calls to Dispose:
DO allow the Dispose(bool) method to be called more than once. The method might choose to do nothing after the first call.
Following these guidelines makes your code consistent with the .NET library and you will avoid any confusion about if your class should be closed or disposed for proper cleanup.
Related
I ran into a problem when the application ends the container does not call the Dispose method of the parts.
Application based on MEF.
When I explicitly call Dispose the container, then matod Dispose is called on the parts, but if you just close the program, the Dispose of the parts will not be called, why?
How to make sure that when you close the program were caused by the Dispose method of all parts of the container MEF?
[Export(typeof(IMyClass))]
[PartCreationPolicy(CreationPolicy.Shared)]
public class MyClass: IDisposable, IMyClass
{
private bool disposed = false;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if(!this.disposed)
{
if(disposing)
{
// Dispose managed resources.
}
disposed = true;
}
}
~MyClass()
{
Dispose(false);
}
}
When I explicitly call Dispose the container, then matod Dispose is called on the parts, but if you just close the program, the Dispose of the parts will not be called, why?
Because disposing the container when you are done with it is mandatory. If your program does not call CompositionContainer.Dispose() before exiting, then that is a bug in your program.
Wim Coenen, thanks, I thought that the destruction of MEF must call Destruct on parts.
I made sure to work the way I need to:
public partial class MyBootstrapper : MefBootstrapper
{
public MyBootstrapper()
{
App.Current.Exit += new ExitEventHandler(Current_Exit);
}
void Current_Exit(object sender, ExitEventArgs e)
{
if (this.Container != null)
this.Container.Dispose();
}
...
We all know that IDisposable interface is using for disposing unmanaged resources.
I have a class which contains following code. here i have implemented the Dispose method from IDisposable interface.
class ClassA:IDisposable
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
What my doubt is why i need to implement the Dispose method from IDisposable interface?. Instead of that i can create my own Dispose method in my class without inheriting from IDisposable interface which i have given below.
for the class below i haven't inherited my class from IDisposable interface. instead of that i created my own dispose method. this also works fine.
class ClassA
{
public ClassA()
{
Console.WriteLine("ClassBeingTested: Constructor");
}
private bool disposed = false;
Image img = null;
public Image Image
{
get { return img; }
}
~ClassA()
{
Console.WriteLine("ClassBeingTested: Destructor");
// call Dispose with false. Since we're in the
// destructor call, the managed resources will be
// disposed of anyways.
Dispose(false);
}
public void Dispose()
{
Console.WriteLine("ClassBeingTested: Dispose");
// dispose of the managed and unmanaged resources
Dispose(true);
// tell the GC that the Finalize process no longer needs
// to be run for this object.
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposeManagedResources)
{
// process only if mananged and unmanaged resources have
// not been disposed of.
if (!this.disposed)
{
Console.WriteLine("ClassBeingTested: Resources not disposed");
if (disposeManagedResources)
{
Console.WriteLine("ClassBeingTested: Disposing managed resources");
// dispose managed resources
if (img != null)
{
img.Dispose();
img = null;
}
}
// dispose unmanaged resources
Console.WriteLine("ClassBeingTested: Disposing unmanaged resouces");
disposed = true;
}
else
{
Console.WriteLine("ClassBeingTested: Resources already disposed");
}
}
// loading an image
public void LoadImage(string file)
{
Console.WriteLine("ClassBeingTested: LoadImage");
img = Image.FromFile(file);
}
}
So can any one tel me tat the reason behind of implementing dispose method from IDisposable interface.
When you implement IDisposable, you can use using for exception-safe disposing.
Two reasons:
Implementing IDisposable expresses intent (this should be disposed) in a conventional manner. It's easy to spot that you should dispose of a resource if it implements IDisposable, whereas relying on other developers to read the documentation carefully is more likely to lead to errors.
That convention is used by the using statement. You should be able to write:
using (ClassA foo = new ClassA())
{
...
}
... but unless you implement IDisposable, you can't.
(Personally I wouldn't include a finalizer, by the way... that's usually only for directly held unmanaged resources; here you should rely on the Image finalizer.)
Although implementing your own dispose method will suffice for any explicit call made to that method but when,after implementig Idispobale, you use a using statement, the built in .Net functionality will invoke your dispose method for you so your code can look like this;
using (ClassA foo = new ClassA())
{
...
}
rather than this
using (ClassA foo = new ClassA())
{
....
foo.Dispose();
}
When you implement IDisposable interface you can use your class in using block, like this:
...
using(var classA = new ClassA())
{
do some stuff
}
after it your Dispose method will be invoked.
It is quite useful.
IDisosable is very useful. For example working with Database connections. It requires all of its implementations to have Dispose method.
It is very useful for working with unmanaged resources, where you have to release them as for the Database connections above, because Garbage Collector is working on managed code (it releases objects where they are not in use anymore), but for unmanaged as C++ application or library (without CLR), it has no idea what is going there. By using its disposable method you say you have finished your work with such a resource and it is being released (freeing memory).
Example (example class and usage):
class Database : IDisposable
{
private SqlConnection _conn;
public Database(string conn_str)
{
// Doing the connectivity
}
public Dataset Read(string sql)
{
SqlCommand cmd = new SqlCommand();
Dataset result = null;
// etc...
return result;
}
public Dispose()
{
_conn.Close();
}
}
using(Database db = new Database(conn_string))
{
Dataset ds = db.Read("SELECT something FROM table");
}
The this approach is very useful. In this statement you init your IDisposable and at the end of statement (not needed to call db.Dispose()) its Dispose() is called and the resources are freed. In this case unmanaged resource may be the .NET SQL Driver, you can use MySQL library, etc.
Three "unwritten" parts of the contract for .net objects are:
If a class implements IDisposable, then once the instance is no longer needed, calling IDisposable.Dispose() on it and abandoning it should take care of all necessary cleanup, regardless of the type of object.
If an object does not implement IDisposable, it may be safely abandoned any time it is no longer needed, without requiring any cleanup.
An object which constructs an instance of a class which implements IDisposable is responsible for ensuring that IDisposable gets called, either by doing it itself when it is done with the object, or ensuring that the reference gets handed off to some other object which will carry out the responsibility.
This is in general a very useful pattern. While there are some rare occasions when it will be impossible for a class to properly implement IDisposable (most commonly because the class exists to expose a complex resource whose cleanup semantics are understood by the user of the class, but not by the class itself), it's very useful to have a unified means of cleanup when things like exceptions occur.
I am using an external API to interface to a FireWire Camera. The API is propably written in C++ but thankfully it brings its own .NET wrapper DLLs. The API requires the following procedure:
ApiResource.Init();
// ... use the ressource here ...
ApiResource.CloseAll();
ApiResource.Release();
Because I need some specific handling code I decided to write a wrapper class for this. I need to keep the ressources open while my Form is open because of Event Handlers, etc. So I thought to make the wrapper easier to use I'd make it a singleton implementing IDisposable so I can wrap it in a using statement. The reason I want a Singleton is to have a controlled and limited way of calling the required API functions:
class Wrapper : IDisposable {
private Wrapper _instance;
public Wrapper Instance
{
get
{
if(_instance == null)
_instance = new Wrapper();
return _instance;
}
}
private Wrapper ()
{
ApiResource.Init();
_disposed = false;
}
// Finalizer is here just in case someone
// forgets to call Dispose()
~Wrapper() {
Dispose(false);
}
private bool _disposed;
public void Dispose()
{
Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if(!_disposed)
{
if(disposing)
{
}
ApiResource.CloseAll();
ApiResource.Release();
_instance = null;
log("Wrapper disposed.");
_disposed = true;
}
}
}
The way I want to use it is this:
using(Wrapper.Instance) {
Application.Run(new Form());
}
I'm quite new to C# so I am very unsure of a couple of things:
Will Dispose() always be called in the above using(Singleton.Instance) { ... }? My logging suggests "yes", but I'm unsure...
Is it safe to wrap Application.Run(...) with a using-statement?
The answer to both of your questions is yes:
Dispose() will always be called when the using block ends, unless Wrapper.Instance was null when the block began.
It is perfectly safe to wrap the call to Run() in a using block.
If a class has a property which contains unmanaged resources. How to make sure no memory leak when using the class
Class A
{
B {get; set;}
}
B contains unmanaged resources.
Implement IDisposable and clean up your unmanaged resources by calling Dispose(), preferably placing the call to Dispose in a finally statement so you clean up resources even in the case of an exception.
C# has a using keyword that you can employ to make sure that the Dispose method is called, even if an exception is thrown.
EDIT: Incorporated call to GC.SuppressFinalize and finalizer implementation per Ran's answer
class A : IDisposable
{
private bool _disposed;
~A()
{
this.Dispose(false);
}
public void Dispose()
{
this.Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!_disposed)
{
if (disposing)
{
// dispose managed resources
}
// clean up unmanaged resources
_disposed = true;
}
}
}
class Program
{
static void Main(string[] args)
{
using (var someInstance = new A())
{
// do some things with the class.
// once the using block completes, Dispose
// someInstance.Dispose() will automatically
// be called
}
}
}
Using IDisposable might not be enough, because it relies on the user remembering to call Dispose or to use using etc.
For a complete solution, combine IDisposable and a finalizer. Like this:
Edit: Made some corrections in the Dispose method based on SpeksETC's comment.
class MyClass : IDisposable
{
~MyClass()
{
Dispose(false);
}
public void Dispose()
{
GC.SupressFinalize();
Dispose(true);
}
protected virtual void Dispose(bool disposing)
{
if (!disposing)
{
// clear unmanaged resources here (can only be called once)
...
}
// dispose called explicitly by the user, clean up managed resources here
...
}
}
This ensures that native resources will always be cleared, even if the user forgets to call Dispose, while still allowing the user to clear the resources early.
The if inside the Dispose implementation is needed because if this class is being finalized, you may not call Dispose on your members because they may have been GC'ed already.
I think it is important to point out that B is a managed resource that only contains unmanaged resources.
Therefore, A should implement IDisposable and dispose of B in its Dispose() method, but does not need a finalizer since it doesn't have any unmanaged resources to clean up - the finalizer needs to be implemented within B itself. Even if you implemented a finalizer it would call a Dispose that looked like this:
protected virtual void Dispose(bool disposing)
{
if (disposing)
{
// dispose called explicitly by the user, clean up managed resources here
b.Dispose()
}
// no unmanaged resources to clean up so do nothing which makes Finalizer unneccesary
...
}
SpeksEtc is correct in that if B contains unmanaged resources then B should ensure there are no leaks not A.
But what are the unmanaged resources and would the SafeHandle class help? Then B would contain a SafeHandle which would contain the unmanaged resource and you wouldn't need to worry about it.
I am using Quartz.NET in an application. What is the proper way to dispose of Quartz.NET.
Right now I am just doing
if (_quartzScheduler != null)
{
_quartzScheduler = null;
}
Is that enough or should I implement a dispose or something in the jobType class?
Seth
scheduler.Shutdown(waitForJobsToComplete: true);
Of course, if you're not on C# 4.0 yet, named parameters don't work:
scheduler.Shutdown(true);
This is not a complete example but might get you on the right path. I would implement something like this:
class customSchedulerClass : IDisposable
{
private Component component = new Component();
private bool disposed = false;
public void scheduleSomeStuff()
{
//This is where you would implement the Quartz.net stuff
}
public void Dispose()
{
Dispose(true);
GC.SupressFinalize(this);
}
private void Dispose(bool disposing)
{
if(!this=disposed)
{
if(disposing)
{
component.dispose;
}
}
disposed = true;
}
}
Then with this you can do cool stuff like using statements:
public static void Main()
{
using (customSchedulerClass myScheduler = new customSchedulerClass())
{
c.scheduleSomeStuff();
}
console.WriteLine("Now that you're out of the using statement the resources have been disposed");
}
So basically by implementing you code while inheriting the functionality of IDisposable you can then us the using statement and when you're done it will cleanly dispose your resources and keep things nice and clean. (Disclaimer, again this is not a complete example, just to get you in the right direction).
The docs don't say anything about IScheduler implementing IDisposable. If you have custom job types that grab and hold resources (file locks, database connections), you can implement IDispoable and override Dispose() on your object to release resources.
Generally we don't need to set an object to null in order to dispose it off.
If an object contains unmanaged resources then it should implement IDisposable (and be called by all its clients).
You can refere this similar post.