I have a class with extensive static members, some of which keep references to managed and unmanaged objects.
For instance, the static constructor is called as soon as the Type is referenced, which causes my class to spin up a blockingQueue of Tasks. This happens when one of the static methods is called, for example.
I implemented IDisposable, which gives me methods to handle disposal on any instance objects I created. However, these methods are never called if the consumer doesn't create any instance objects from my class.
How and where do I put code to dispose of references maintained by the static portion of my class? I always thought that disposal of static-referenced resources happened when the last instance object was released; this is the first time I've ever created a class where no instances may ever be created.
The static variable of your class are not garbage collected until the app domain hosting your class is unloaded. The Dispose() method will not be called, because it is an instance method, and you said that you wouldn't create any instances of your class.
If you would like to make use of the Dispose() method, make your object a singleton, create one instance of it, and dispose of it explicitly when your application is about to exit.
public class MyClass : IDisposable {
public IList List1 {get; private set;}
public IDictionary<string,string> Dict1 {get; private set;}
public void Dispose() {
// Do something here
}
public static MyClass Instance {get; private set;}
static MyClass() {
Instance = new MyClass();
}
public static void DisposeInstance() {
if (Instance != null) {
Instance.Dispose();
Instance = null;
}
}
}
public class Logger : IDisposable
{
private string _logDirectory = null;
private static Logger _instance = null;
private Logger() : this(ConfigurationManager.AppSettings["LogDirectory"])
{
AppDomain.CurrentDomain.ProcessExit += CurrentDomain_ProcessExit;
}
private Logger(string logDirectory)
{
}
public static Logger Instance
{
get
{
if (_instance == null)
_instance = new Logger();
return _instance;
}
}
private void CurrentDomain_ProcessExit(object sender, EventArgs e)
{
Dispose();
}
public void Dispose()
{
// Dispose unmanaged resources
}
}
You should dispose this objects manually, there is no way to create a "finalizer" for static resources.
If you really want to have static members which keep references to unmanaged objects
just create a method for disposing the unmanaged objects and "force" consumer to use it on exit.
By "force" I mean document your class with a paragraph that states "when" and "why" to use this "dispose" method.
Do it either if you are the sole consumer (or your code...) or you plan to distribute your class.
Also try to use a somehow descriptive name (to that "dispose" method) such as "DisposeStatics", "AlwaysDispose", "DisposeAtEnd" etc.
Related
Edit: My bad, no strage events behavior. Error was somewhere else in code. Thx everybody for help. Please ignore this question
Please can someone explain to me what is happening here. I'm experiencing an unexpected event behaviour.
There is a singleton class:
internal class QueueListener
{
private static readonly object QueueChangeLock = new object();
private readonly List<IQueuedJobExecutioner> jobsQueue = new List<IQueuedJobExecutioner>();
// Here comes singleton private constructor, Instance property, all classic.
// Important line in constructor is this:
QueueManager.NewJobQueued += NewJobQueuedHandler;
private void NewJobQueuedHandler(object sender, NewJobQueuedEventArgs args)
{
lock (QueueChangeLock)
{
// This is the problematic place, note this!
jobsQueue.Add(args.QueuedJobExecutioner);
}
}
}
Now there is a second class:
public class QueueManager
{
public static event NewJobQueuedEventHandler NewJobQueued;
protected void RaiseNewJobQueuedEvent(IQueuedJobExecutioner queuedJobExecutioner)
{
if (NewJobQueued != null)
{
NewJobQueued(this, new NewJobQueuedEventArgs { QueuedJobExecutioner = queuedJobExecutioner });
}
}
}
Both classes reside on a server. Via WCF calls client executes sth like new QueueManager().MyMethod(), which calls RaiseNewJobQueuedEvent.
Everything works fine, however if two events are raised almost at the same time, I see in debugger the following at the problematic place (see comment in QueueListener):
First event comes. jobsQueue has no members.
jobsQueue.Add() is executed. jobsQueue has 1 member.
Second event comes. jobsQueue has no members! How? It's in a singleton and we just added a member!
jobsQueue.Add() is executed. jobsQueue has 1 member. Again. Member added in step 2 has been lost.
Not judging the design itself (it has some "historical" reasons), why exactly is this happening? Is this expected behavior and event somehow gets at some point a snapshot of jobsQueue or this is nonesense and I'm just missing some part of the puzzle?
Edit:
I'd say it is a singleton, and is implemented like this (these lines were omitted in original post):
class QueueListener
{
private static readonly object SyncRoot = new object();
private QueueListener()
{
//...
}
public static QueueListener Instance
{
get
{
if (instance == null)
{
lock (SyncRoot)
{
if (instance == null)
{
instance = new QueueListener();
}
}
}
return instance;
}
}
}
Yuval is correct, your class is not a singleton. A singleton is created when you have a public static method to create an instance and a private constructor. The private constructor ensures that the only way to create an instance is through the public method.
Please see https://msdn.microsoft.com/en-us/library/ff650316.aspx for more details.
Your QueueListener class is not actually a singleton. What that means for you is that you are creating multiple instances of it. To fix that you have to add the static keyword in the class declaration and declare a static constructor as well. Try changing your class to what is shown below:
internal static class QueueListener
{
private static readonly object QueueChangeLock = new object();
private static readonly List<IQueuedJobExecutioner> jobsQueue = new List<IQueuedJobExecutioner>();
// This is the singleton constructor that will be called
static QueueListener()
{
// Here comes singleton private constructor, Instance property, all classic.
// Important line in constructor is this:
QueueManager.NewJobQueued += NewJobQueuedHandler;
}
// Rest of class code...
}
I have a class like that:
class ContentManager : IDisposable
{
List<int> idlist = new List<int>();
public int Load(string path)
{
//Load file, give content, gets an id
//...
int id = LoadFile(myfilecontent);
idlist.Add(id);
return id;
}
public void Dispose()
{
//Delete the given content by id, stored in idlist
foreach(int id in idlist)
{
DeleteContent(id);
}
}
}
I want to make it static, because i need only one instance and can access the function from every other class without giving an instance.
I can make every variable in it static and the functions static.
But my problem is this IDisposable. I cannot have Interfaces in static classes. How can i do some action at the end? I mean i can remove that interface but leave the function in it and use my main class and when my main class gets disposed i call ContentManager.Dispose(). But when i forget that in my main...
Do you have a good solution for that? Make sure that Dispose is called every time when the program gets closed?
Edit: I load data in a graphic card and get the pointer back. When my application closes, i need to delete the contents from the graphics card. To be safe, everything is deleted, i use dispose.
I would leave your class as a non-static class and implement the singleton pattern. I added an example of how you would use it as singleton:
public class ContentManager : IDisposable
{
private List<int> idlist = new List<int>();
private static ContentManager instance;
private ContentManager () {}
public static ContentManager Instance
{
get
{
if (instance == null)
{
instance = new ContentManager ();
}
return instance;
}
}
public int Load(string path)
{
int id = LoadFile(myfilecontent);
idlist.Add(id);
return id;
}
public void Dispose()
{
foreach(int id in idlist)
{
DeleteContent(id);
}
}
}
You should just not implement IDisposable. The thing is, that interfaces purpose is to ensure that clean up is done when an instance goes out of scope. There are no instances, and because of that IDisposable doesn't really apply.
The main thing that IDisposable gives you is that if you allocate your instance in a using statement the dispose call is added for you by the compiler. Again, you no longer have instances so it has no purpose. Instead you should just have your own dispose/clean up method and document it's purpose. If you think that is too error prone (relying on documentation is obviously less ideal than having the compiler/runtime enforce something) then you probably want to follow the singleton pattern as suggested in another answer.
Why do you need an IDisposable interface in this case? Static finalizers and destructors are not possible, because types are only unloaded when the AppDomain shuts down so anyway the fact that you could use IDisposable would not be useful.
If you really need to implement IDisposable and want to have just one instance of the class maybe it is a better solution to use a Singleton pattern?
Your class could then look like this:
class ContentManager : IDisposable
{
List<int> idlist = new List<int>();
static ContentManager instance=null;
ContentManager()
{
}
public static ContentManager Instance
{
get
{
if (instance==null)
{
instance = new ContentManager();
}
return instance;
}
}
public int Load(string path)
{
//Load file, give content, gets an id
//...
int id = LoadFile(myfilecontent);
idlist.Add(id);
return id;
}
public void Dispose()
{
//Delete the given content by id, stored in idlist
foreach (int id in idlist)
{
DeleteContent(id);
}
}
}
It is not thread-safe but could be enough in your scenario.
Try turning your class into a Singleton.
i have a Singleton object that holding a proxy to WCF methods. This Singleton object called from several points in code include as COM object.
My Question is:
Is The GC can decide to free the object even if i will use it later (for example in COM) ?
How can i Decide When Dispose() This object? The use of ~Finalizer() method is good idea ? or may be the GC will decide to finalize it before i finished use it ?
Is the call GC.KeepAlive(this) can resolve the problem ?
Thanks!
EDIT:
public class Singleton
{
private static Singleton instance = null;
public static Singleton GetInstance()
{
if (instance == null)
{
lock (syncObject)
{
if (instance == null)
{
instance = new Singleton();
}
}
}
return instance;
}
public void CallWcfMethod()
{
// ....
}
}
public class Class1
{
Singleton instance = Singleton.GetInstance();
public void CallWcfMethod()
{
instance.CallWcfMethod();
}
}
[ComVisible(true)]
public class Class2
{
Singleton instance = Singleton.GetInstance();
public void CallWcfMethod()
{
instance.CallWcfMethod();
}
}
If your instance is declared as static, it will not be collected as long as the AppDomain is still alive at which point you seldom need to do any specific clean up.
If you want to stop garbage collection you just need a way to keep a reference to the object, the easiest and the one most suitable for singletons is this.
public class Singleton
{
public static Singleton Instance
{
get{ return sInstance;}
}
public void CallWcfMethod()
{
// ....
}
private static Singleton sInstance;
}
So that way you don't need to store it in every class of yours, just call Singleton.Instance.CallWcfMethod();
I am using a Singleton instance created out of a nested class. This instance holds some static collections which are cleared when the Singleton is disposed, but the problem is I get a reference to non-null disposed Singleton which is not properly garbage collected.
I would like to know how to completely dispose and garbage collect my Singleton instance so that when the instance is queried again after dispose (and setting to null) a new Instance is created.
I am using the following nested pattern for Singleton instance:
public class SingletonClass : IDisposable
{
private List<string> _collection;
private SingletonClass()
{
}
public static SingletonClass Instance
{
get
{
return Nested.Instance; //line 1 - this line returns the non-null instance after dispose and setting the Singleton instance to null which is causing problems
}
}
private void Init()
{
_collection = new List<string>();
//Add data to above collection
}
public void Dispose()
{
//Release collection
_collection.Clear();
_collection = null;
}
class Nested
{
static Nested()
{
Instance = new SingletonClass();
Instance.Init();
}
internal static readonly SingletonClass Instance;
}
}
The problem at line 1 is that after dispose of SingletonClass from client class, the _collection object becomes null while the SingletonClass instance remains non-null even after setting = null.
You'll only need to implement System.IDisposable if you fulfill following basic requirement:
The primary use of this interface is to release unmanaged resources.
Then I would go for the destructor of the class and call Dispose() in the Microsoft Docs Example.
Otherwise
The garbage collector automatically releases the memory allocated to a
managed object when that object is no longer used.
(which won't be the case with a real singleton, unless the process ends)
You may be better off, if you are using sth like this
class PseudoSingleton<T>
where T : new()
{
private readonly object _lock = new object();
private T _instance;
public T Instance
{
get
{
lock (this._lock)
{
if (this._instance != null)
{
this._instance = new T();
}
return this._instance;
}
}
}
public void Reset()
{
lock (this._lock)
{
this._instance = null;
}
}
}
I am using .net 1.1. I have a session class in which I have stored many static variables that hold some data to be used by many classes.
I want to find a simple way of destroying this class instead of resetting every variable one by one. For example if there is a static class MyStatic, I would have liked to destroy/remove this class from the memory by writing MyStatic = null, which is not currently possible,
Additional question.
The idea of singleton is good, but I have the following questions:
If singleton is implemented, the 'single' object will still remain in the memory. In singleton, we are only checking if an instance is already existing. how can i make sure that this instance variable also gets destroyed.
I have a main class which initializes the variable in the static class. Even if I plan to implement a Rest() method, I need to call it from a method, for eg, the destructor in the main class. But this destructor gets called only when GC collects this main class object in the memory, which means the Reset() gets called very late
thanks
pradeep
Don't use a static class to store your variables. Use an instance (and make it a singleton if you only want one instance at any given time.) You can then implement IDisposible, and just call Dispose() when you want to destroy it.
For more information check out this site: http://csharpindepth.com/Articles/General/Singleton.aspx
EDIT
The object is still subject to garbage collection, so unless you are using lots of unmanaged resources, you should be fine. You can implement IDisposible to clean up any resources that need to be cleaned up as well.
Instead of a static class, have a static instance of a class:
class Foo
{
public int Something;
public static Foo Instance = new Foo();
public void Reset()
{
Instance = new Foo();
}
}
void test
{
int i = Foo.Instance.Something;
}
You can also delegate to an instance of the class:
class Foo
{
public int Something
{
get { return instance.something; }
}
private int something;
private static Foo instance = new Foo();
public void Reset()
{
instance = new Foo();
}
}
void test
{
int i = Foo.Something;
}
There's no way to destroy a static unless it resides in a separate AppDomain in which case you can get rid of it by unloading the AppDomain. However it is usually better to avoid statics.
EDIT: Additional question
When the singleton is no longer referenced it will be collected just as everything else. In other words, if you want it collected you must make sure that there are no references to it. It goes without saying that if you store a static reference to your singleton, you will have the same problem as before.
Use a Singleton like ktrauberman said, and have an initialization method or a reset method. You only have to write the code once and call the method.
You destroy objects, not classes. There's nothing wrong with static classes--C# provides them for a reason. Singletons are just extra overhead, unless you actually need an object, e.g. when you have to pass the object as a parameter.
Static classes contain only static variables. These variables tend to last for the lifetime of the app, in which case you don't have to worry about disposing referenced objects, unless you have a mild case of OCD. That just leaves the case where your static class allocates and releases resources throughout its lifetime. Dispose of these objects in due course as you usually would (e.g., "using...").
The best way in your condition is to have an Reset() method built-in as well, which can reset the values of the class.
class myclass
{
private static myclass singleobj = null;
private myclass(){}
public static myclass CreateInstance()
{
if(singleobj == null)
singleobj = new myclass();
return singleobj
}
}
Building on Ahemd Said's answer: (and props to him!)
class Singleton
{
private static Singleton instance = null;
private Singleton(){} // private constructor: stops others from using
public static Singleton Instance
{
get { return instance ?? (instance = new Singleton()); }
set {
if (null != value)
{ throw new InvalidValueException(); }
else
{ instance = null; }
}
}
}
void SampleUsage()
{
Singleton myObj = Singleton.Instance;
// use myObj for your work...
myObj.Instance = null; // The set-operator makes it ready for GC
}
(untested... but mostly right, I think)
You could also add in usage of the IDispose interface for more cleanup.
You can create a method in the static class which resets the values of all properties.
Consider you have a static class
public static class ClassA
{
public static int id=0;
public static string name="";
public static void ResetValues()
{
// Here you want to reset to the old initialized value
id=0;
name="";
}
}
Now you can use any of the below approaches from any other class to reset value of a static class
Approach 1 - Calling directly
ClassA.ResetValues();
Approach 2 - Invoking method dynamically from a known namespace and known class
Type t1 = Type.GetType("Namespace1.ClassA");
MethodInfo methodInfo1 = t1.GetMethod("ResetValues");
if (methodInfo1 != null)
{
object result = null;
result = methodInfo1.Invoke(null, null);
}
Approach 3 - Invoking method dynamically from an assembly/set of assemblies
foreach (var Ass in AppDomain.CurrentDomain.GetAssemblies())
{
// Use the above "If" condition if you want to filter from only one Dll
if (Ass.ManifestModule.FullyQualifiedName.EndsWith("YourDll.dll"))
{
List<Type> lstClasses = Ass.GetTypes().Where(t => t.IsClass && t.IsSealed && t.IsAbstract).ToList();
foreach (Type type in lstClasses)
{
MethodInfo methodInfo = type.GetMethod("ResetValues");
if (methodInfo != null)
{
object result = null;
result = methodInfo.Invoke(null, null);
}
}
break;
}
}
Inject the objects into the static class at startup from a non static class that implements IDisposable, then when your non static class is destroyed so are the objects the static class uses.
Make sure to implement something like "Disable()" so the static class is made aware it's objects have just been set to null.
Eg I have a logger class as follows:
public static class Logger
{
private static Action<string, Exception, bool> _logError;
public static void InitLogger(Action<string, Exception, bool> logError)
{
if(logError != null) _logError = logError;
}
public static void LogError(string msg, Exception e = null, bool sendEmailReport = false)
{
_logError?.Invoke(msg, e, sendEmailReport);
}
In my constructor of my Form I call the following to setup the logger.
Logger.InitLogger(LogError);
Then from any class in my project I can do the following:
Logger.LogError("error",new Exception("error), true);