Updated: December 2010
Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection.
Assembly: mscorlib (in mscorlib.dll)
The method is used to perform cleanup operations on unmanaged resources held by the current object before the current object is destroyed. The method is protected and, therefore, is accessible only through this class or a derived class.
This method is automatically called after an object becomes inaccessible, unless the object has been exempted from finalization by a call to GC.SuppressFinalize. During shutdown of an application domain, is automatically called on objects that are not exempt from finalization, even those that are still accessible. is automatically called only once on a given instance, unless the object is re-registered using a mechanism such as ReRegisterForFinalize and GC.SuppressFinalize has not been subsequently called.
Every implementation of in a derived type must call its base type's implementation of . This is the only case in which application code is allowed to call .
Because the C# compiler does not allow you to directly implement the method, a C# destructor automatically calls the destructor of its base class.
operations have the following limitations:
The exact time when the finalizer executes during garbage collection is undefined. Resources are not guaranteed to be released at any specific time, unless calling a Close method or a Dispose method.
The finalizers of two objects are not guaranteed to run in any specific order, even if one object refers to the other. That is, if Object A has a reference to Object B and both have finalizers, Object B might have already finalized when the finalizer of Object A starts.
The thread on which the finalizer is run is unspecified.
The method might not run to completion or might not run at all in the following exceptional circumstances:
Another finalizer blocks indefinitely (goes into an infinite loop, tries to obtain a lock it can never obtain and so on). Because the runtime attempts to run finalizers to completion, other finalizers might not be called if a finalizer blocks indefinitely.
The process terminates without giving the runtime a chance to clean up. In this case, the runtime's first notification of process termination is a DLL_PROCESS_DETACH notification.
The runtime continues to Finalize objects during shutdown only while the number of finalizable objects continues to decrease.
If or an override of throws an exception, and the runtime is not hosted by an application that overrides the default policy, the runtime terminates the process and no active try-finally blocks or finalizers are executed. This behavior ensures process integrity if the finalizer cannot free or destroy resources.Notes to Implementers
does nothing by default. It must be overridden by a derived class only if necessary, because reclamation during garbage collection tends to take much longer if a operation must be run.
A type must implement when it uses unmanaged resources such as file handles or database connections that must be released when the managed object that uses them is reclaimed.
can take any action, including resurrecting an object (that is, making the object accessible again) after it has been cleaned up during garbage collection. However, the object can only be resurrected once; cannot be called on resurrected objects during garbage collection.
Destructors are the C# mechanism for performing cleanup operations. Destructors provide appropriate safeguards, such as automatically calling the base type's destructor. In C# code, cannot be called or overridden.
The following example verifies that the method is called when an object that overrides is destroyed. Note that, in a production application, the method would be overridden to release unmanaged resources held by the object. Also note that the C# example provides a destructor instead of overriding the method.
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