I have a windows service, which contains a singleton which in turn uses some loggers, message queue listeners and so on. Those classes implements IDisposable. Should I implement IDisposable in singleton itself or do something else to ensure that after service stop/crashing everything will be okay with native resources?
The singleton is implemented like this:
public class Temp
{
private static readonly Lazy<Temp> instance = new Lazy<Temp>(() => new Temp());
private Temp()
{
// create IDisposable objects which use native resources
}
public static Temp Instance
{
get
{
return instance.Value;
}
}
}
I'd rather not implement IDisposable on singleton: IDisposable provokes developer to Dispose the (single) instance:
using(var temp = Temp.Instance) {
...
}
which leads to (possible) crash in some other part of the application (since the single Temp instance has been disposed):
Temp.Instance.SomeFucntion(); // <- possible fail, since Temp.Instanceis disposed
In some rare case if you have to release some resouces aquired, I'd use ProcessExit
event
public class Temp {
private static readonly Lazy<Temp> instance = new Lazy<Temp>(() => new Temp());
private void OnProcessExit(Object sender, EventArgs e) {
// Release native resource if required:
// some resources e.g. files will be closed automatically,
// but some e.g. transactions should be closed (commit/rollback) manually
try {
...
}
finally {
AppDomain.CurrentDomain.ProcessExit -= OnProcessExit;
}
}
private Temp() {
// create IDisposable objects which use native resources
// If you have to release some resouces on exit
AppDomain.CurrentDomain.ProcessExit += OnProcessExit;
}
public static Temp Instance {
get {
return instance.Value;
}
}
}
No; Singleton shouldn't implement IDisposable. What if someone disposes the instance prematurely when others are in need of that?
Also note that implementing IDisposable will not help you when your service is crashed/stopped. You'll have to dispose it manually! but you can't find right time to do it.
If a type will be returned from a factory that will sometimes need to be cleaned up when the caller is done with them, the type should implement IDisposable. If a particular factory returns a shared singleton object that doesn't actually need any resources, the object returned by the factory should have a Dispose method which silently does nothing. If the factory needs to provide access to a shared singleton resources (e.g. an immutable bitmap stored in a GDI object), it should return a wrapper which will notify the factory when it its Dispose method is called; the factory can then maintain a reference count of wrapper objects and clean up the resource once it knows that no more wrappers will be created and all existing wrappers have been disposed.
Related
This question already has answers here:
Proper use of the IDisposable interface
(20 answers)
Closed 2 years ago.
I've gone through many article which says the purpose of IDisposable is to close the unmanaged objects like DB connections and Third party reports.But my question is why should I define Dispose method if I can handle the unmanaged objects in my methods without defining Dispose() method?
For an example,
class Report : IDisposable
{
public void GenerateReport()
{
Report rpt=new Report() //unmanaged object created
rpt.Dispose(); // Disposing the unmanaged object
}
private void Dispose()
{
//not sure why this block is needed
}
}
Is my understanding correct?
You're correct that you wouldn't need the implement IDisposable in your example. The example where you would is if you're keeping a long lived object for the life of the class you've written. So say you had this:
public class Report : IDisposable
{
private Stream _reportStream; // This variable lives a long time.
public void WriteToStream(byte[] data)
{
_reportStream.Write(data, 0, data.Length);
}
public void Dispose()
{
_reportStream?.Dispose();
}
}
This is a fairly simple example, but it shows that _reportStream lives for the length of the class and needs to get cleaned up and garbage collected at the same time as the class. There's nothing stopping you from creating a public method called CleanupObject() to do the same thing, but then people can't use a using block to have the Runtime call the Dispose() automatically:
using (var myReport = new Report())
{
// do a bunch of things with myReport;
} // Here the runtime will call myReport.Dispose() for you.
// myReport isn't accessible from here, as it was declared in the using block
The class that implements the IDisposable interface can be used in the using block. A big plus of this solution is that after leaving the block the Dispose method will be automatically called on the object created in this area. That way, we can only use classes that implement the IDisposable interface.
//example :
using(var dClean= new DisposableClean())
{
//after leaving this using dClean will be automatically destroyed
}
The object that you've created needs to expose some method, not necessary named Dispose(). You could also call it Clean(). Dispose() is the conventional name.
Garbage Collector(GC), available throughout the .Net framwork, works well enough to be easily forgotten. However, it is worth learning to work with him well and use his possibilities. For this purpose, the correct implementation of the IDisposable interface is necessary, the basic form of which is sometimes insufficient if we consider the proper release of managed and unmanaged resources.
This is extanded version which can be very useful in this case.
In a way an answer to you question:
public class DisposableExtended: IDisposable
{
private bool isDisposed = false;
public void Dispose ()
{
this.Dispose (true);
GC.SupressFinalize (this);
}
protected void Dispose (bool disposing)
{
if (! this.isDisposed)
{
if (disposing)
{
// here we release managed resources (standard classes)
}
// here we release unmanaged resources (e.g. streams, etc..)
{
}
}
this .isDisposed = true;
}
~ DisposableExtended ()
{
this.Dispose (false);
}
Yes, you can define your own way to release resources but many existing code use this way. If you share your code to people, remember to tell them to dispose in your way.
One "profit" of implementing IDisposable is that you can call Dispose indirectly by use a language construct such as using.
For example:
using(Stream s = File.OpenRead("HelloWorld.bin"))
{
//Do stuffs
}
My application is using 3 layers: DAL / Service / UL.
My typical DAL class looks like this:
public class OrdersRepository : IOrdersRepository, IDisposable
{
private IDbConnection _db;
public OrdersRepository(IDbConnection db) // constructor
{
_db = db;
}
public void Dispose()
{
_db.Dispose();
}
}
My service calls the DAL class like this (injecting a database connection):
public class ordersService : IDisposable
{
IOrdersRepository _orders;
public ordersService() : this(new OrdersRepository(new Ajx.Dal.DapperConnection().getConnection()))
{
}
public ordersService(OrdersRepository ordersRepo)
{
_orders = ordersRepo;
}
public void Dispose()
{
_orders.Dispose();
}
}
And then finally within my UI layer, this is how I access my service layer:
public class OrdersController : Controller, IDisposable
{
//
// GET: /Orders/
private ordersService _orderService;
public OrdersController():this(new ordersService())
{
}
public OrdersController(ordersService o)
{
_orderService = o;
}
void IDisposable.Dispose()
{
_orderService.Dispose();
}
}
This all works good. But as you can see, I am relying on IDisposable within every layer. UI disposes service object and then service object disposes DAL object and then DAL object disposes the database connection object.
I am sure there has to be a better way of doing it. I am afraid users can forget to dispose my service object (within UI) and I will end up with many open database connections or worse. Please advise the best practice. I need a way to auto-dispose my database connections OR any other unmanaged resources (files etc).
Your question comes back to the principle of ownership:
he who has ownership of the resource, should dispose it.
Although ownership can be transferred, you should usually not do this. In your case the ownership of the IDbConnection is transferred from the ordersService to the OrdersRepository (since OrdersRepository disposes the connection). But in many cases the OrdersRepository can't know whether the connection can be disposed. It can be reused throughout the object graph. So in general, you should not dispose objects that are passed on to you through the constructor.
Another thing is that the consumer of a dependency often can't know if a dependency needs disposal, since whether or not a dependency needs to be disposed is an implementation detail. This information might not be available in the interface.
So instead, refactor your OrdersRepository to the following:
public class OrdersRepository : IOrdersRepository {
private IDbConnection _db;
public OrdersRepository(IDbConnection db) {
_db = db;
}
}
Since OrdersRepository doesn't take ownership, IDbConnection doesn't need to dispose IDbConnection and you don't need to implement IDisposable. This explicitly moves the responsibility of disposing the connection to the OrdersService. However, ordersService by itself doesn't need IDbConnection as a dependency; it just depends on IOrdersRepository. So why not move the responsibility of building up the object graph out of the OrdersService as well:
public class OrdersService : IDisposable {
private readonly IOrdersRepository _orders;
public ordersService(IOrdersRepository ordersRepo) {
_orders = ordersRepo;
}
}
Since ordersService has nothing to dispose itself, there's no need to implement IDisposable. And since it now has just a single constructor that takes the dependencies it requires, the class has become much easier to maintain.
So this moves the responsibility of creating the object graph to the OrdersController. But we should apply the same pattern to the OrdersController as well:
public class OrdersController : Controller {
private ordersService _orderService;
public OrdersController(ordersService o) {
_orderService = o;
}
}
Again, this class has become much easier to grasp and it doesn't needs to dispose anything, since it doesn't has or took ownership of any resource.
Of course we just moved and postponed our problems, since obviously we still need to create our OrdersController. But the difference is that we now moved the responsiblity of building up object graphs to a single place in the application. We call this place the Composition Root.
Dependency Injection frameworks can help you making your Composition Root maintainable, but even without a DI framework, you build your object graph quite easy in MVC by implementing a custom ControllerFactory:
public class CompositionRoot : DefaultControllerFactory {
protected override IController GetControllerInstance(
RequestContext requestContext, Type controllerType) {
if (controllerType == typeof(OrdersController)) {
var connection = new Ajx.Dal.DapperConnection().getConnection();
return new OrdersController(
new OrdersService(
new OrdersRepository(
Disposable(connection))));
}
else if (...) {
// other controller here.
}
else {
return base.GetControllerInstance(requestContext, controllerType);
}
}
public static void CleanUpRequest() }
var items = (List<IDisposable>)HttpContext.Current.Items["resources"];
if (items != null) items.ForEach(item => item.Dispose());
}
private static T Disposable<T>(T instance)
where T : IDisposable {
var items = (List<IDisposable>)HttpContext.Current.Items["resources"];
if (items == null) {
HttpContext.Current.Items["resources"] =
items = new List<IDisposable>();
}
items.Add(instance);
return instance;
}
}
You can hook your custom controller factory in the Global asax of your MVC application like this:
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
ControllerBuilder.Current.SetControllerFactory(
new CompositionRoot());
}
protected void Application_EndRequest(object sender, EventArgs e)
{
CompositionRoot.CleanUpRequest();
}
}
Of course, this all becomes much easier when you use a Dependency Injection framework. For instance, when you use Simple Injector (I'm the lead dev for Simple Injector), you can replace all of this with the following few lines of code:
using SimpleInjector;
using SimpleInjector.Integration.Web;
using SimpleInjector.Integration.Web.Mvc;
public class MvcApplication : System.Web.HttpApplication
{
protected void Application_Start()
{
var container = new Container();
container.RegisterPerWebRequest<IDbConnection>(() =>
new Ajx.Dal.DapperConnection().getConnection());
container.Register<IOrdersRepository, OrdersRepository>();
container.Register<IOrdersService, OrdersService>();
container.RegisterMvcControllers(Assembly.GetExecutingAssembly());
container.Verify();
DependencyResolver.SetResolver(
new SimpleInjectorDependencyResolver(container));
}
}
There are a few interesting things going on in the code above. First of all, the calls to Register tell Simple Injector that they need to return a certain implementation should be created when the given abstraction is requested. Next, Simple Injector allows registering types with the Web Request Lifestyle, which makes sure that the given instance is disposed when the web request ends (just as we did in the Application_EndRequest). By calling RegisterMvcControllers, Simple Injector will batch-register all Controllers for you. By supplying MVC with the SimpleInjectorDependencyResolver we allow MVC to route the creation of controllers to Simple Injector (just as we did with the controller factory).
Although this code might be a bit harder to understand at first, the use of a Dependency Injection container becomes really valuable when your application starts to grow. A DI container will help you keeping your Composition Root maintainable.
Well, if you're really paranoid about that you can use the finalizer (destructor) to automatically execute the Dispose when the object is being garbage collected. Check this link which explains basically all you need to know about IDisposable, skip to the Examples section if just want a quick sample how to do that. The finalizer(destructor) is the ~MyResource() method.
But any way, you should always encourage the consumers of your libraries to use correctly the Dispose. The automatic cleaning up, by means of garbage collector still presents flaws. You don't know when the garbage collector will do its job, so if you get lots of these classes instantiated and used, then forgotten, in a short time, you may still be in trouble.
I am using C#. Is it advised to unit test dispose methods? If so why, and how should one test these methods?
Yes, but it might be hard. There are two things that can generally happen in Dispose implementation:
Unmanaged resources are released.
In this case it's pretty hard to verify that the code called, for example, Marshal.Release. A possible solution is to inject an object that can do the disposing and pass a mock to it during testing. Something to this effect:
interface ComObjectReleaser {
public virtual Release (IntPtr obj) {
Marshal.Release(obj);
}
}
class ClassWithComObject : IDisposable {
public ClassWithComObject (ComObjectReleaser releaser) {
m_releaser = releaser;
}
// Create an int object
ComObjectReleaser m_releaser;
int obj = 1;
IntPtr m_pointer = Marshal.GetIUnknownForObject(obj);
public void Dispose() {
m_releaser.Release(m_pointer);
}
}
//Using MOQ - the best mocking framework :)))
class ClassWithComObjectTest {
public DisposeShouldReleaseComObject() {
var releaserMock = new Mock<ComObjectReleaser>();
var target = new ClassWithComObject(releaserMock);
target.Dispose();
releaserMock.Verify(r=>r.Dispose());
}
}
Other classes' Dispose method is called
The solution to this might not be as simple as above. In most cases, implementation of Dispose is not virtual, so mocking it is hard.
One way is to wrap up those other objects in a mockable wrapper, similar to what System.Web.Abstractions namespace does for HttpContext class - i.e. defines HttpContextBase class with all virtual methods that simply delegates method calls to the real HttpContext class.
For more ideas on how to do something like that have a look at System.IO.Abstractions project.
Certainly can't hurt. Client code may try to use an object of your class after it has disposed of it. If your class is composed of other IDisposable objects, you should always be throwing the ObjectDisposedException exception if it is in a state which it is no longer usable.
Of course, you should only be testing the external state of your object. In the example below, I've made the property Disposed external to give me the state.
Consider:
internal class CanBeDisposed : IDisposable
{
private bool disposed;
public bool Disposed
{
get
{
if (!this.disposed)
return this.disposed;
throw new ObjectDisposedException("CanBeDisposed");
}
}
public void Dispose()
{
this.Dispose(true);
GC.SuppressFinalize(this);
}
protected virtual void Dispose(bool disposing)
{
if (!this.disposed)
{
if (disposing)
{
//// Dispose of managed resources.
}
//// Dispose of unmanaged resources.
this.disposed = true;
}
}
}
So how I would test this is thus:
CanBeDisposed cbd;
using (cbd = new CanBeDisposed())
{
Debug.Assert(!cbd.Disposed); // Best not be disposed yet.
}
try
{
Debug.Assert(cbd.Disposed); // Expecting an exception.
}
catch (Exception ex)
{
Debug.Assert(ex is ObjectDisposedException); // Better be the right one.
}
If your class creates and works with unmanaged resources, then you should definitely ensure that Dispose works as you expect it to - although it could be argued it is more of an integration test due to the type of hoops you're going to have to jump through.
If your class only creates / uses managed resources ( i.e. they implement IDisposable ) then all you really need to ensure is that the Dispose method on these resources is invoked at the correct time - if you are using some form of DI then you can inject a mock and assert that Dispose was called.
Look at the complexity of your dispose methods - if they are only a couple of lines long with maybe 1 condition, ask yourself if there really is a benefit in unit testing them.
Big yes - if your situation requires you to implement a Dispose function - you better make sure it does what you think!
For example, we have classes that coordinate database tasks (think SSIS packages, but with SqlConnection and SqlCommand and SqlBulkCopy etc.).
If I don't properly implement my Dispose, I could have an uncommitted SqlTransaction, or dangling SqlConnection. This would be VERY bad if I were running multiple instances of these database tasks in series.
As a practical tip (because yes, you should test Dispose()) my experience has been that there are two ways to do so without too much hassle.
IDisposer
The first follows Igor's accepted answer - inject something like an IDisposer, so that you can call
public void Dispose()
{
_disposer.Release(_disposable);
}
where
public interface IDisposer
{
void Release(IDisposable disposable);
}
Then all you need to do is mock the IDisposer and assert that it's called once and you're golden.
Factory
The second, and my personal favourite, is to have a factory that creates the thing you need to test disposal of. This only works when the factory produces a mockable type (interface, abstract class), but hey, that's almost always the case, especially for something that's to be disposed. For testing purposes, mock the factory but have it produce a mock implementation of the thing you want to test disposal of. Then you can assert calls to Dispose directly on your mock. Something along the lines of
public interface IFooFactory
{
IFoo Create(); // where IFoo : IDisposable
}
public class MockFoo : IFoo
{
// ugly, use something like Moq instead of this class
public int DisposalCount { get; privat set; }
public void Dispose()
{
DisposalCount++;
}
}
public class MockFooFactory
{
public MockFoo LatestFoo { get; private set; }
public IFoo Create()
{
LatestFoo = new MockFoo();
return LatestFoo;
}
}
Now you can always ask the factory (which will be available in your test) to give you the latest MockFoo, then you dispose of the outer thing and check that DisposalCount == 1 (although you should use a test framwork instead, e.g. Moq).
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.
In C# it is possible to create weak references to objects as described here:
WeakReference Class
In .net some classes also implement the IDisposable interface. Calling the Dispose method of this interface is performed to manually dispose of any managed or unmanaged resources currently being held onto. An example might be a Bitmap object or class.
If I assign an object that implements IDisposable to a weak reference, will Dispose be called if the weak reference collects the object?
In general, the answer is indeed No.
However, a properly implemented class that implements IDisposable using the IDisposable pattern (hopefuly all .NET classes do this). Would also implement finalizer which is called when the object is garbage collected and inside the finalizer, it would call Dispose. So, for all proper implementations of IDisposable, the Dispose method will be called.
(Note: the counter-example by Fernando is not implementing IDisposable properly)
GC does not ever call Dispose. Dispose must be called by user code.
No. Simple like that ;)
No. Check this test:
class Program {
static void Main(string[] args) {
Test test = new Test();
Console.WriteLine(test.Disposable == null);
GC.Collect();
Console.WriteLine(test.Disposable == null);
Console.ReadLine();
}
}
public class Test {
private WeakReference disposable = new WeakReference(new WeakDisposable());
public WeakDisposable Disposable {
get { return disposable.Target as WeakDisposable; }
}
}
public class WeakDisposable : IDisposable {
~WeakDisposable() {
Console.WriteLine("Destructor");
}
public void Dispose() {
Console.WriteLine("Dispose");
}
}
The output is:
False
True
Destructor
As you can see, the execution never hits the Dispose method.