I've got a class with one IDisposable member variable initialized in-line, and another IDisposable in the constructor.
Will Dispose() be called if the constructor throws? If so, then I presume the null check is necessary...? If not, then how does the in-line member get disposed?
sealed class SomeDisposable : IDisposable { ... }
sealed class Foo : IDisposable
{
readonly SomeDisposable sd1= new SomeDisposable(); // this doesn't throw
readonly SomeDisposable sd2;
public Foo()
{
sd2 = new SomeDisposable(); // assume this throws
// how does sd1 get Dispose()d?
}
public void Dispose()
{
sd1.Dispose();
if (sd2!= null) // is this null check necessary?
sd2.Dispose();
}
}
There is at present no way in C# to safely initialize an IDisposable with an in-line initializer except through a nasty hack involving ThreadStatic variables. The constructor must be called via factory method that creates a disposal-manager object and stores a reference in a thread-static field. Field initializers can then wrap their value in a call to a static method which will add them to the disposal-manager object.
The actual field-initializer syntax ends up being pretty reasonable:
DisposalManager Cleaner = DisposalManager.CurrentManager;
DType1 DField1 = DisposalManager.Guard(new DType1);
DType2 DField2 = DisposalManager.Guard(new DType2);
so does the Dispose cleanup:
void Dispose(bool disposing)
{
Cleaner.Cleanup(disposing);
}
Unfortunately, the needs to have every single call to Guard do its own access to the thread-static field, and to have all constructor calls wrapped in factory methods, makes the construct rather ugly. Too bad, since being able to use a single line to declare, create, and clean up a field is much nicer than having to do those things at three separate places in the code.
Lets assume you're using the following code in the form:
var foo = new Foo(someByteArray);
And your constructor throws an exception, then foo will be null, because the class constructor didn't complete. Any attempt to call it's Dispose will cause a NRE to occur.
Interesting question.
Tried this:
try
{
//caller
using (var x = new Disposable1()) { }
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
public class Disposable1 : IDisposable
{
private Disposable2 first = new Disposable2();
private Disposable2 second;
public Disposable1()
{
second = new Disposable2("Goodbye!");
}
public void Dispose()
{
Debug.WriteLine("Disposable1.Dispose()");
first.Dispose();
if (second != null)
second.Dispose();
}
}
public class Disposable2 : IDisposable
{
public string Whatever { get; set; }
public Disposable2() { Whatever = "Hello!"; }
public Disposable2(string whatever)
{
Whatever = whatever;
throw new Exception("Doh!");
}
public void Dispose()
{
Debug.WriteLine("Disposable2.Dispose()" + Whatever);
}
}
...and the output was...
Doh!
So it does appear that neither member is initialized or disposed.
Related
When combining a using statement with a fluent api that can potentially throw, the lowered code will never call dispose correctly.
If I have the following class that exposes a fluent interface:
public class Wrapper : IDisposable
{
private bool _isAdded;
public Wrapper Add()
{
_isAdded = true;
return this;
}
public void Dispose() => Console.WriteLine("dispose called");
public Wrapper ThrowIfAdded() => _isAdded ? throw new Exception() : this;
}
and I call it with the following:
using var willNotDispose = new Wrapper().Add().ThrowIfAdded();
the lowered code will result in the Dispose call occurring after the fluent method chain is completed.
Wrapper willNotDispose = new Wrapper().Add().ThrowIfAdded();
try
{
}
finally
{
if (willNotDispose != null)
{
((IDisposable)willNotDispose).Dispose();
}
}
Alternatively, if the call to .ThrowIfAdded() is done outside of the initial using declaration,
using var willDispose = new Wrapper().Add();
willDispose.ThrowIfAdded();
the lowered code is generated as expected.
Wrapper willDispose = new Wrapper().Add();
try
{
willDispose.ThrowIfAdded();
}
finally
{
if (willDispose != null)
{
((IDisposable)willDispose).Dispose();
}
}
While I understand why this is occurring, it isn't desirable. Is there any way to coerce the former initialization to compile to the latter? Ideally, it would be an attribute or form of compiler hint that would result in:
Wrapper willDispose = default;
try
{
willDispose = new Wrapper().Add().ThrowIfAdded();
}
finally
{
if (willDispose != null)
{
((IDisposable)willDispose).Dispose();
}
}
which I would have expected the original example to compile to in the first place.
As pointed out in the comments, there is pre-existing guidance that when an exception is thrown in a constructor, it should be explicitly handled and the resources cleaned up.
This extends to CA2000 analysis that states:
When constructors that are protected by only one exception handler are
nested in the acquisition part of a using statement, a failure in the
outer constructor can result in the object created by the nested
constructor never being closed. In the following example, a failure in
the StreamReader constructor can result in the FileStream object never
being closed. CA2000 flags a violation of the rule in this case.
using (StreamReader sr = new StreamReader(new FileStream("C:/myfile.txt", FileMode.Create)))
{ ... }
While a Fluent API throwing an exception is not explicitly either a constructor or nested constructor throwing an exception, it should be treated the same since the object will be created and mutated outside of the try/finally block.
As a result, any method that can throw must first call dispose before allowing the exception to propagate.
public class Wrapper : IDisposable
{
private bool _isDisposed;
private bool _isAdded;
public Wrapper Add()
{
_isAdded = true;
return this;
}
public void Dispose()
{
if (_isDisposed)
{
return;
}
_isDisposed = true;
Console.WriteLine("dispose called");
}
public Wrapper ThrowIfAdded()
{
if (_isAdded)
{
Dispose();
throw new Exception();
}
return this;
}
}
This correctly assures that in cases where .Added() is called, .ThrowIfAdded() will dispose prior to throwing.
If .Added() is not called, the instance will be disposed at the end of the block as expected.
At the moment I have the following class.
class BaseClass : IDisposable
{
private static List<BaseClass> instances = new List<BaseClass>();
protected BaseClass()
{
instances.Add(this);
}
~BaseClass()
{
Dispose();
}
public void Dispose()
{
instances.Remove(this);
}
}
So the lifetime of every class that inherit the BaseClass is infinitely until I close the program or I will call Dispose explicity.
Can I prevent this behaviour, so that lifetime is back to normal? (of course without removing the possibility to access the derived objects, otherwise my question make no sense)
I add the static List, to handle various actions to all classes that inherit BaseClass.
Edit
class DerivedClass : BaseClass
{
}
//This case works
using (DerivedClass _dc = new DerivedClass())
{
//Do something with object
}
//This object will live forever, because it is internally in the static list
//That behaviour is not desired
DerivedClass dc = new DerivedClass();
How I can get the bahaviour that DerivedClass dc calls his destructor after the normal lifetime (as it would not be in the list)?
Background
I want to fill the Properties of the derived classes with values from a config file and do it in base class. But if the config file changed, I have to change all properties of alll derived classes. So if you know a way to get all objects that implements the base class and needs to be changed, let me know it.
Update
Solution 1: Based on my question
With help from Steve Mitcham (Go to post) I found out how I can make a weak reference with few lines of code:
class BaseClass : IDisposable
{
private static List<GCHandle> handles = new List<GCHandle>();
protected BaseClass()
{
this.handle = GCHandle.Alloc(this, GCHandleType.Weak);
handles.Add(this.handle);
}
~BaseClass()
{
Dispose();
}
public void Dispose()
{
if (handle.IsAllocated)
{
//Do Something more to Dispose the Object
//...
handle.Free();
handles.Remove(handle);
}
}
public void DoSomethingWithTheList()
{
foreach (GCHandle handle in handles)
{
BaseClass bc = (BaseClass)handle.Target;
//Do something
}
}
}
Now If I call GC.Collect(); it will collect my unused derived classes (so I think the garbage collector will collect my objects normally as well) because the object itself has no reference in a list.
Thank you!
Solution 2: Subsrciber / Broadcaster Pattern
With this pattern it is simple too. Additionally the derived class can get the info if the values are changed.
Thank you Alireza (Goto post) and Thangadurai.
class ConfigurationBroadcaster
{
string path = "";
public string Path
{
get { return path; }
set
{
bool changed = path != value;
path = value;
if(changed)
if (ChangedConfigurationValues != null)
{
Delegate[] invocationList = ChangedConfigurationValues.GetInvocationList();
foreach (var item in invocationList)
{
Type t = item.Target.GetType();
PropertyInfo[] pInfos = t.GetProperties();
foreach (PropertyInfo pInfo in pInfos)
{
//new object() have to be the value from config file
//5 is used to set Width and Height from BroadcastSubscriber for this example
pInfo.SetValue(item.Target, 5/* new object()*/, null);
}
}
ChangedConfigurationValues(this, new EventArgs());
}
}
}
public event EventHandler ChangedConfigurationValues;
}
class BaseBroadcastSubscriber
{
ConfigurationBroadcaster broadcaster;
protected BaseBroadcastSubscriber(ConfigurationBroadcaster broadcaster)
{
this.broadcaster = broadcaster;
this.broadcaster.ChangedConfigurationValues += new EventHandler(broadcaster_ChangedConfigurationValues);
}
void broadcaster_ChangedConfigurationValues(object sender, EventArgs e)
{
Console.WriteLine("Configuration values changed");
}
}
class BroadcastSubscriber : BaseBroadcastSubscriber
{
int width,height;
public int Width
{
get { return width; }
set { width = value; }
}
public int Height
{
get { return height; }
set { height = value; }
}
public BroadcastSubscriber(ConfigurationBroadcaster broadcaster)
: base(broadcaster)
{
}
}
Without seeing more of your program it would be difficult to determine whether your approach could be improved. However, without fundamentally changing your design I would use WeakReferences to track your objects. The UpdateClasses method is to simulate your reconfigure action.
class BaseClass : IDisposable
{
private WeakReference<BaseClass> myReference;
private static List<WeakReference<BaseClass>> instances = new List<WeakReference>();
public static UpdateClasses(MyData stuff)
{
foreach(var ref in instances)
{
BaseClass target;
if (ref.TryGetTarget(out target))
{
// code to update target here
}
}
}
protected BaseClass()
{
myReference = new WeakReference<BaseClass>(this,true);
instances.Add(myReference);
}
~BaseClass()
{
Dispose();
}
public void Dispose()
{
instances.Remove(myReference);
}
}
The weak references will not keep your objects alive. When they get garbage collected they will remove their references from the instance list. Note, however, that this implementation will cause your objects to stay alive in the garbage collector longer than normal due to the requirement for the finalizer, and this may decrease the performance of the application over time.
Despite Steve Mitchman's answer, you could design a broadcaster class providing an event which gets fired whenever a change in config file is detected. Derived classes (objects) could subscribe to this event and unsubscribe upon being get GC collected or finalized. This approach follows open/closed principle very well.
When your BaseClass instance is off, that is both when you call the Dispose and when the instance itself is destroyed. These cases are normal.
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 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.
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);