From the resource clean-up perspective, why there are Response.Close() and Response.Dispose() and which one is more comprehensive (call the other one) ?
Where both methods are provided the implementation of Dispose should call Close. It is a good idea to use the using statement to ensure that Disposeand therefore Close is called, even if there is an exception.
In other words do this:
using (Response response = ...)
{
// ...
}
Not this:
Response response = ...;
// ...
response.Close(); // If there is an exception this might never get called!
One difference between closing and disposing an object is that when you dispose an object it usually is not possible to use the object any more (attempting to do so may cause an ObjectDisposedException to be thrown), but after calling Close it may be possible to still use the object.
Note that if you are talking about ASP.NET then you shouldn't normally call Close or Dispose on the Response object.
From the Design Guidelines for Developing Class Library on Implementing Finalize and Dispose to Clean Up Unmanaged Resources
Occasionally a domain-specific name is
more appropriate than Dispose. For
example, a file encapsulation might
want to use the method name Close. In
this case, implement Dispose privately
and create a public Close method that
calls Dispose. The following code
example illustrates this pattern. You
can replace Close with a method name
appropriate to your domain. This
example requires the System namespace.
/ Do not make this method virtual.
// A derived class should not be allowed
// to override this method.
public void Close()
{
// Call the Dispose method with no parameters.
Dispose();
}
Typically I've seen close whenever the resource can be opened or re-opened, since it gives nice symmetry to the method names.
Response.Close() closes the socket connection to a client.
Response.Dispose() is method which implements IDisposable interface and releases allocated resources.
I think Response.Close() is called from Response.Dispose() method.
For more detailed information you can use Reflector
Related
For example, if I want to cancel some operation in a Dispose() call (which can be called multiple times), then do I need to write
public void Dispose()
{
if (!cancellationTokenSource.IsCancellationRequested)
{
cancellationTokenSource.Cancel();
}
}
or is it enough with the simpler
public void Dispose()
{
cancellationTokenSource.Cancel();
}
(You are welcome to comment on whether it is wise or not to cancel things in a Dispose method, but that is not the point of this question.)
Yes.
But only if the CancellationTokenSource has not been disposed yet.
From the reference source:
ThrowIfDisposed();
// ...
// fast-path test to check if Notify has been called previously
if (IsCancellationRequested)
return;
This seems more a question about the Dispose pattern, then about CancellationToken or anything else. And I am uncertain if you implemented said pattern properly. Here is the official MS Document on the mater:
https://learn.microsoft.com/en-us/dotnet/standard/design-guidelines/dispose-pattern
And here my interpretation:
There is two levels of Disposing: Dispose and Finalizsation. As the code for both is very similar, often they are combiend into one function (in C# usually it is Dispose one). The main difference is if you relay it to contained classes. You always relay a Dispose call(the relay is usually what Dispose is about). You never relay a Finalization call (Finalisation is between that instance and the GC only).
There are also two cases: One in wich you handle Unmanaged resources directly. And one in wich you handle just another Disposeable class.
Unamanged resource directly
In this case the first thing you do is implement a Finalizer, so at least the GC can reliably clean this up. Then you implement IDisposeable as an additional feature so programmers can use stuff like the using pattern to have it cleaned up deterministic at runtime.
Handling something that implements IDisposeable
You have a resource that implements IDisposeable (say like a Filestream Reference). You implement IDisposeable in your class for the sole purpose of relaying the Dispose() call to said FileStream. This is the way more common case. It would guess it makes about 95-99% of all Dispose Implementations.
One thing to keep in mind here is that "Dispose" and "Finalize" often implies lower level cleanup. A SQLConenction you call dispose on will be closed first (if nessesary). A Filehandle you Dispose off will also first be closed. Even if calling cancellationTokenSource.Cancel was not repeatable, cancellationTokenSource.Dispose should call Cancel as part of it's operation and should be Repeatable. The class itself does implement IDisposeable. And if any class does, it is usually saver to just call Dispose rather then manually doing the cleanup manually via Cancel: https://learn.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokensource?view=netframework-4.7.2
Hi
When i use following code:
myManualResetEvent.Dispose();
Compiler gives this error:
'System.Threading.WaitHandle.Dispose(bool)' is inaccessible due to its protection level.
howevr following line works fine:
((IDisposable)myManualResetEvent).Dispose();
is it the correct way to dispose or at runtime it might crash in some scenerios.
Thanks.
The designers of the .NET Base Class Library decided to implement the Dispose method using explicit interface implementation:
private void IDisposable.Dispose() { ... }
The Dispose method is private and the only way to call it is to cast the object to IDisposable as you have discovered.
The reason this is done is to customize the name of the Dispose method into something that better describes how the object is disposed. For a ManualResetEvent the customized method is the Close method.
To dispose a ManualResetEvent you have two good options. Using IDisposable:
using (var myManualResetEvent = new ManualResetEvent(false)) {
...
// IDisposable.Dispose() will be called when exiting the block.
}
or calling Close:
var myManualResetEvent = new ManualResetEvent(false);
...
// This will dispose the object.
myManualResetEvent.Close();
You can read more in the section Customizing a Dispose Method Name in the design guideline Implementing Finalize and Dispose to Clean Up Unmanaged Resources on MSDN:
Occasionally a domain-specific name is more appropriate than Dispose. For example, a file encapsulation might want to use the method name Close. In this case, implement Dispose privately and create a public Close method that calls Dispose.
WaitHandle.Close
This method is the public version of
the IDisposable.Dispose method
implemented to support the IDisposable
interface.
According to the documentation, WaitHandle.Dispose() and WaitHandle.Close() are equivalent. Dispose exists to allow closing though the IDisposable interface. For manually closing a WaitHandle (such as a ManualResetEvent), you can simply use Close directly instead of Dispose:
WaitHandle.Close
[...]
This method is the public version of the IDisposable.Dispose method implemented to support the IDisposable interface.
Lets say I have a class that associates itself with another class. It would look something like the following:
public class DisposableClassOne : IDisposable
{
private class mDisposableClassTwo;
public DisplosableClassOne(DisposableClassTwo dcTwoInjected)
{
mDisposableClassTwo = dcTwoInjected;
}
public void Dispose()
{
// Should I dispose here? or make caller dispose of dcTwoInjected
//mDisposableClassTwo.Dispose();
}
}
Should I call the Dispose method of mDisposableClassTwo or should I make the caller handle it like this?
using(DisposableClassTwo dcTwoInjected = new DisposableClassTwo())
using(DisposableClassOne dcOne = new DisposableClassOne(dcTwoInjected))
{
// do stuff with dcOne
}
I'm thinking making the caller handle it is the best way to go, but I think by putting the call in the Dispose method it guarantees that it will get called. Is there a better way to handle this?
If the class you are creating logically owns(1) the constructor injected resource then it should dispose of it internally. If it does not own the resource, then it should do nothing, and rely on the consumer to decide when it should be disposed.
If your class owns a reference to an unmanaged resource, you may also need to implement a finalizer (destructor) since there is no guarantee that anyone will ever call your Dispose method at all.
In general, you want to avoid cases where the caller must decide when they should dispose of an object passed to the constructor of a class. It's possible for the caller to dispose of the resource prematurely (or hold on to it longer than necessary). This is not always an easy thing to achieve in certain designs ... sadly, the Disposable Object pattern doesn't always compose cleanly with itself.
(1) By ownership I mean that your class controls the lifetime of the resource which it is passed and no other code holds a reference to it. If any other code (whose lifetime is not tied to the lifetime of your class) holds a reference to the resource and will use it independently, then you are not the owner of that resource.
I think it is a life-time decision you have to make in your design.
Is DisposableClassOne Disposable BECAUSE it references a DisposableClassTwo?
And,
Does a DisposableClassTwo have a lifetime independent of DisposableClassOne?
To me, the answers to these two questions varies in each class design. The StreamReader/Writer is a great example of the first question being 'yes' and the second 'no' - no one would expect to use a Stream inside a StreamReader once the Reader is done with it, so Reader disposes it.
But what if DisposableClassTwo was some other resource - maybe a file refernece you passed to several classes in turn to 'do something to'. In that case, you don't want it disposed until you're ready and DisposableClassOne might be long gone by then.
The standard I'm familiar with is to use the Disposable pattern. Have a virtual Dispose(bool disposing) method. The Dispose() method calls Dispose(true) and the finalizer calls Dispose(false).
Then, in the main disposal method:
if (disposing)
{
// Dispose of the referenced object, as well.
}
StreamWriter & StreamReader follow this pattern. If you explicitely call Dispose(), they also dispose the underlying Stream. If you let the finalizer do your cleanup, they leave it alone.
Alternatively, you could add a property: DisposeChild, if true, dispose the child object, if not, leave it alone.
I also agree with rcravens. Under almost all circumstances, an object should be disposed within the same scope where it was instantiated.
To use IDisposable objects properly, one must follow the principle "Would the last one out please turn off the lights". There are a few nice scenarios, and an icky one:
The creator of an object gives it to another object (the "recipient") but the creator of the first object controls the recipient's lifetime, and can know when the recipient will no longer need the passed object. In that case, the creator of the original object takes care of Dispose.
The creator of an object gives it to the recipient, and the recipient knows that nobody else will use the object once it's been handed over. In that case, the recipient will call Dispose when it's done with the object.
An object recipient may sometimes be used in ways that match #1 and sometimes in ways that match #2, but the supplier of the object will know when it's given which situation applies. This situation may be handled by telling the recipient whether or not the recipient should Dispose of the object it is given.
The supplier and recipient will both want to use the object, but may have no idea which is going to outlive the other. This is the toughest situation.
I tend to like the approach suggested in #3. Sometimes situation #4 applies, though. One way of handling that is for the recipient of the object to fire an event when it's done with the object. That event can Interlocked.Decrement a counter indicating how many objects are still using the passed object. Once that counter hits zero, the object may be deleted.
It is better not to dispose any external references, those would be disposed automatically by the caller itself.
See this thread, in which it is suggested that only member variable needs to be disposed:
Finalize/Dispose pattern in C#
The concept of "cleanup by owner" is far too common to be ignored. Ownership must be more than just coincidence.
If you want software that is easier to maintain, avoid side effects that may be incorrectly interpreted. The Stream vs StreamReader example is a great one... both are IDisposable, and as the caller, I'm making both, so in no way should I ever give myself a pass at disposing either of them. Doing so would violate the abstraction, tying my calling code's knowledge to the particulars of the stream class' implementation (which could change over time, academically).
The easiest answer is to have the two usings(), even if you then go and make (and document!) that the second IDisposable will dispose of the first.
Which one do I call?
Is it necessary to call both?
Will the other throw an exception if I have already called one of them?
Close() and Dispose(), when called on a MemoryStream, only serve to do two things:
Mark the object disposed so that future accidental usage of the object will throw an exception.
Possibly1 release references to managed objects, which can make the GC's job a bit easier depending on the GC implementation. (On today's GC algorithms it makes no real difference, so this is a point for an academic discussion and has no significant real-world impact.)
MemoryStream does not have any unmanaged resources to dispose, so you don't technically have to dispose of it. The effect of not disposing a MemoryStream is roughly the same thing as dropping a reference to a byte[] -- the GC will clean both up the same way.
Which one do I call? Is it necessary to call both?
The Dispose() method of streams delegate directly to the Close() method2, so both do exactly the same thing.
Will the other throw an exception if I have already called one of them?
The documentation for IDisposable.Dispose() specifically states it is safe to call Dispose() multiple times, on any object3. (If that is not true for a particular class then that class implements the IDisposable interface in a way that violates its contract, and this would be a bug.)
All that to say: it really doesn't make a huge difference whether you dispose a MemoryStream or not. The only real reason it has Close/Dispose methods is because it inherits from Stream, which requires those methods as part of its contract to support streams that do have unmanaged resources (such as file or socket descriptors).
1 Mono's implementation does not release the byte[] reference. I don't know if the Microsoft implementation does.
2 "This method calls Close, which then calls Stream.Dispose(Boolean)."
3 "If an object's Dispose method is called more than once, the object must ignore all calls after the first one."
None of the above. You needn't call either Close or Dispose.
MemoryStream doesn't hold any unmanaged resources, so the only resource to be reclaimed is memory. The memory will be reclaimed during garbage collection with the rest of the MemoryStream object when your code no longer references the MemoryStream.
If you have a long-lived reference to the MemoryStream, you can set that reference to null to allow the MemoryStream to be garbage collected. Close and Dispose free neither the steam buffer nor the MemoryStream object proper.
Since neither Stream nor MemoryStream have a finalizer, there is no need to call Close or Dispose to cause GC.SuppressFinalize to be called to optimize garbage collection. There is no finalizer to suppress.
The docs for MemoryStream put it this way:
This type implements the IDisposable interface, but does not actually have any resources to dispose. This means that disposing it by directly calling Dispose() or by using a language construct such as using (in C#) or Using (in Visual Basic) is not necessary.
You can use the using block for this. It will automatically call Dispose when it goes outside of its scope.
Example:
using (MemoryStream ms = new MemoryStream())
{
// Do something with ms..
}
// ms is disposed here
Hope this helped.
Use using block so that your object is disposed if its implements IDisposable interface
the following code is Stream.Dispose from reflector as you can see, you don't need to close if you dispose (which is implicit when using using)
public void Dispose()
{
this.Close();
}
Which one do I call?
Any of them.
Is it necessary to call both?
No, either one is sufficient.
Will the other throw an exception if I have already called one of them?
No, disposable pattern declares that subsequent calls to Dispose don't cause negative effects.
Calling Close() will internally call Dispose() to release the resources.
See this link for more information:
msdn
Calling only Dispose() will do the trick =)
In .NET 3.5 (haven't checked other versions), methods are called in the following order when disposing a MemoryStream:
Stream.Dispose()
simply calls Close
Stream.Close()
calls Dispose(true), then GC.SuppressFinalize(this)
MemoryStream.Dispose(true)
sets _isOpen , _writable, and _expandable flags to false
Stream.Dispose(true)
closes async event if active
As a first solution, it's recommended to use using statements wherever possible. This is described here: http://msdn.microsoft.com/en-us/library/yh598w02.aspx
When the lifetime of an IDisposable object is limited to a single method, you should declare and instantiate it in the using statement. The using statement calls the Dispose method on the object in the correct way, and (when you use it as shown earlier) it also causes the object itself to go out of scope as soon as Dispose is called. Within the using block, the object is read-only and cannot be modified or reassigned.
Coming to the question now, as others suggested in most .NET framework classes, there is no difference between Close() and Dispose() and it doesn't matter which of the two methods you call. You should call one but not both. However, there are exceptions.
There are exceptions; for example, System.Windows.Forms.Form and System.Data.SqlClient.SqlConnection have different behavior for Close() and Dispose().
For complete details, you can check here: https://blogs.msdn.microsoft.com/kimhamil/2008/03/15/the-often-non-difference-between-close-and-dispose/
This question already has answers here:
What are the uses of "using" in C#?
(29 answers)
Closed 8 years ago.
Are there particular instances where I should (or shouldn't?) be using "using" blocks:
using(SomeType t = new SomeType()){
...
}
Some objects need some action to be taken when you have finished with them. Usually this is because the object uses some kind of resource that needs to be disposed of. For example, if you have a file object of class File, and this object opens a file from the file system, the file in the file system will need to be closed again.
If you just left the file object, and forgot to call file.Close() it wouldn't be cleaned up until the Garbage Collector (GC) ran and worked out nothing was still using the file object. When the Garbage Collector runs should be left to the Common Language Runtime (CLR) to decide. If the GC doesn't run for quite a while after you have finished with the file, the file could remain open potentially for a long time. This can pose a big problem if there are many file objects, or if something wants to open a file, but can't because the file object you left is still hanging around.
To solve this problem, C# has the IDisposable interface. This has one method called Dispose. Classes that require some cleanup implement this Dispose method. This gives you a standard way for cleaning up any objects that use resources. There are a lot of classes that need to have Dispose called. The problem with this is that code gets covered with calls to Dispose, and they are tricky to follow because the place where you new'ed the object and call Dispose to clean it up are different. So, you had to look around the code a lot and be very careful to check there were calls to Dispose in the right place.
To solve this problem C# introduced the 'using' keyword. You can put a 'using' keyword around where you new an object, and this ensures Dispose will be called on it for you. It guarantees that Dispose will be called whatever happens... even if there is an exception thrown within the body of the using statement.
So, you should use 'using' when you want to be sure an object that allocates resources will be cleaned up.
using can only be used for objects that are declared on the stack, i.e. in a function. It doesn't work for objects that are declared as members of a class. For them, you have to call Dispose yourself. You may have to implement Dispose in your class so that in can call Dispose on any member objects it has that require it.
Common objects that need using called on them are: Files, Database connections, Graphics objects such as Pen and Brush.
Sometimes it is also used when you want two operations to happen together. For example if you want to write a log statement when a block of code is entered and when it exits you could write a log class that you could use like this:
using( Log log = new Log("Doing stuff") )
{
// Stuff
}
The constructor for the log class could be made to write out the message, and the Dispose method could also write it out. Implement the finalizer (~Log) to assert if the Dispose method doesn't get called to ensure the 'using' is remembered around the 'new Log'.
When the SomeType class implements IDisposable.
Use using whenever the type implements IDisposable, unless you're going to wrap it in a try/catch block anyway, then you might as well (depending on what look you prefer) use a finally block.
I see plenty of other answers indicated when you should have a using statement. I want to address when specifically should not have a using statement:
If you need to use your object outside of the scope of the current function, don't have a using block. Good example are a factory method that returns a database connection or a method that needs to return a datareader. In either of those cases if you create your object with a using statement it would be disposed before the method returned, and therefore not usable outside the method.
Now, you still want to be sure that those objects are disposed, so you still might want a using statement somewhere. Just don't include it in the method where the object is actually created. Instead, you can wrap the function call itself in a using statement.
When SomeType implements IDisposable.
That is a clue to you the developer that SomeType uses unmanaged resources that need to be cleaned up.
Example:
using(SqlConnection MyConnection = new SqlConnection("Connection string"))
{
MyConnection.Open();
//...
// 1. SQLConnection is a type that implements IDisposable
// 2. So you can use MyConnection in a using statement
// 3. When using block finishes, it calls Dispose method of
// SqlConnection class
// 4. In this case, it will probably close the connection to
// the database and dispose MyConnection object
}
You can create your own objects that implements IDisposable:
public class MyOwnObjectThatImplementsIDisposable : IDisposable
{
//... some code
public void Dispose()
{
// Put here the code you want to be executed when the
// using statement finish.
}
}
So you could use an object of MyOwnObjectThanImplementsIDisposable type in a using statement:
using(MyOwnObjectThatImplementsIDisposable MyObject = new MyOwnObjectThatImplementsIDisposable)
{
// When the statement finishes, it calls the
// code you´ve writed in Dispose method
// of MyOwnObjectThatImplementsIDisposable class
}
Hope this helps
In this context the using statement is handy for types that implement IDisposable. When the code block exits the scope of the using statement, Dispose() is called implicitly. It's a good habit when working with objects you want to dispose immediately after use.
One specific instance in which you should be careful using a using block is with a WCF Service Client.
As noted in this MSDN article, wrapping a WCF client (which does implement IDisposable) in a using block could mask any errors which result in the client being left in a faulted state (like a timeout or communication problem). Long story short, when Dispose() is called, the client's Close() method fires, but throws and error because it's in a faulted state. The original exception is then masked by the second exception. Not good.
There are various workarounds out there, including one in the MSDN article itself. Others can be found at IServiceOriented and blog.davidbarret.net.
I prefer the last method, myself.
If you want a summary rule. Anytime an object using IDisposable where you would not have a catch, use using. Using, essentially, is this pattern:
try
{
//instantiate and use object
}
finally
{
//dispose object
}
If you do not need a catch, using can save you typing, which is a good thing.
The primary rule is:
* Use USING statement when objects implements IDisposable interface.
This interface provides the Dispose method, which should release the object's resources. If this method is not invoked then the object will stay in memory as long, as CLR wants to perform garbage collection. If the programmer use the USING statement then on the end the object will be disposed, and all resources will be free.
It is very important that all resources that are no longer in use be free as soon as possible.
For more information about it just visit this link: microsoft
Maybe it is worth mentioning that underlying reason for adding “using” lo C# languge is following: some resources can be scarce enough that it doesn’t make sense to wait for GC to call IDisposable. For example, DB connections. If you use try/catch/finally you won’t end up with a dangling connection, but connection will be left hanging until GC doesn’t kick in and this can take a while (if you do not close it explicitly). IF you use "using" (excuse the pun) you will release the connection immediately even if you forgot to close it and even if some exception occured inside the using block.
Another reason, as previous post mentions, is that programmers do not always use finally to clean up. If not using finally in the case of exception you end up with leaking resources…
One situation is when you want to do something at the beginning of a code block, and then undo it at the end of the block, unconditionally (even if there is a throw).
The ctor for the disposable class that you build (and call within the using) would perform the action, and then the Dispose method would undo that action. This is typically how I use it.
Other people has mentioned about "IDisposable" already.
But one of the caveats when using "using" statement is that,
any exceptions thrown within "using" will not be caught
even thought "SomeType" will be disposed regardless.
So in the following snippet,
using (SomeType t = new SomeType()){
throw new Exception("thrown within using");
}
throw new Exception("thrown within using"); should not be disregarded.
I would also add that use a using() statement if something implements IDispose and also if that something you want to dispose of holds on to NON-MANAGED resources like database connections and file handles.
If it's a normal object with say a List<T>, where T is like a Customer object that holds names and address, then you don't need to. The garbage collector is smart enough to manage this for you. But the garbage collector WILL NOT return connections to the connection pool or close file handles.