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Creating QR Code in Visual Studio .NET // Allocate this array after the garbage objects

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Automatic Memory Management (Garbage Collection)
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It is also worth mentioning that C# offers a fixed statement that effectively pins an object over a block of code . Here is some code that demonstrates its use:
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unsafe public static void Go() { // Allocate a bunch of objects that immediately become garbage for (Int32 x = 0; x < 10000; x++) new Object(); IntPtr originalMemoryAddress; Byte[] bytes = new Byte[1000];
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// Allocate this array after the garbage objects
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// Get the address in memory of the Byte[] fixed (Byte* pbytes = bytes) { originalMemoryAddress = (IntPtr) pbytes; } // Force a collection; the garbage objects will go away & the Byte[] might be compacted GC.Collect(); // Get the address in memory of the Byte[] now & compare it to the first address fixed (Byte* pbytes = bytes) { Console.WriteLine("The Byte[] did{0} move during the GC", (originalMemoryAddress == (IntPtr) pbytes) " not" : null); } }
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Using C# s fixed statement is more efficient that allocating a pinned GC handle . What happens is that the C# compiler emits a special pinned flag on the pbytes local variable . During a garbage collection, the garbage collector examines the contents of this root, and if the root is not null, it knows not to move the object referred to by the variable during the compaction phase . The C# compiler emits IL to initialize the pbytes local variable to the address of the object at the start of a fixed block, and the compiler emits an IL instruction to set the pbytes local variable back to null at the end of the fixed block so that the variable doesn t refer to any object, allowing the object to move when the next garbage collection occurs . Now, let s talk about the next two flags, Weak and WeakTrackResurrection . These two flags can be used in scenarios when interoperating with unmanaged code, but they can also be used in scenarios that use only managed code . The Weak flag lets you know when an object has been determined to be garbage but the object s memory is not guaranteed to be reclaimed yet . The WeakTrackResurrection flag lets you know when an object s memory has been reclaimed . Of the two flags, the Weak flag is much more commonly used than the WeakTrackResurrection flag . In fact, I ve never seen anyone use the WeakTrackResurrection flag in a real application . Let s say that Object-A periodically calls a method on Object-B . However, the fact that Object-A has a reference to Object-B forbids Object-B from being garbage collected, and in some rare scenarios, this may not be desired; instead, we might want Object-A to call Object-B s method if Object-B is still alive in the managed heap . To accomplish this scenario, Object-A would call GCHandle s Alloc method, passing in the reference to Object-B and the Weak flag . Object-A would now just save the returned GCHandle instance instead of the reference to Object-B .
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Part IV
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At this point, Object-B can be garbage collected if no other roots are keeping it alive . When Object-A wants to call Object-B s method, it would query GCHandle s read-only Target property . If this property returns a non-null value, then Object-B is still alive . Object-A s code would then cast the returned reference to Object-B s type and call the method . If the Target property returns null, then Object-B has been collected and Object-A would not attempt to call the method . At this point, Object-A s code would probably also call GCHandle s Free method to relinquish the GCHandle instance . Since working with the GCHandle type can be a bit cumbersome and because it requires elevated security to keep or pin an object in memory, the System namespace includes a WeakReference class to help you . This class is really just an object-oriented wrapper around a GCHandle instance: logically, its constructor calls GCHandle s Alloc, its Target property calls GCHandle s Target property, and its Finalize method calls GCHandle s Free method . In addition, no special permissions are required for code to use the WeakReference class because the class supports only weak references; it doesn t support the behavior provided by GCHandle instances allocated with a GCHandleType of Normal or Pinned . The downside of the WeakReference class is that its object must be allocated on the heap . So the WeakReference class is a heavier-weight object than a GCHandle instance . Also, the WeakReference class doesn t implement the dispose pattern (which is a bug), so there is no way for you to free the GCHandle table entry explicitly; you have to wait for a garbage collection to kick in so that its Finalize method is called . The WeakReference class was introduced in version 1 .0 of the .NET Framework; therefore, it is not generic (generics were introduced in version 2 .0) . So, I have created a little, lightweight structure that I sometimes use to put a compile-time type-safe wrapper around the WeakReference class:
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internal struct WeakReference<T> : IDisposable where T : class { private WeakReference m_weakReference; public WeakReference(T target) { m_weakReference = new WeakReference(target); } public T Target { get { return (T)m_weakReference.Target; } } public void Dispose() { m_weakReference = null; } }
Occasionally, developers ask me if there is a way to create a weak delegate where one object will register a callback delegate with some other object s event but the developer doesn t want the registering of the event to forcibly keep the object alive . For example, let s say that we have a class called DoNotLiveJustForTheEvent . We want to create an instance of this class and have it register a callback method with a Button object s Click event . However, we don t want the Button object s event to keep the DoNotLiveJustForTheEvent object alive . If the DoNotLiveJustForTheEvent object has no other reason to live, then we want it to get garbage collected, and it will just not receive a notification the next time the Button object raises its Click event . Let me show you how you might accomplish this: First, here is the definition of the DoNotLiveJustForTheEvent class:
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