Difference Between Similar Terms and Objects

Difference Between Dispose and Finalize

In programming languages, an object can have only variable during its existence, after instantiation it cannot be modified. So same memory cell cannot be allocated to new values, thus some sort of automated memory management is required to manage the unused spaces. These unused spaces are called garbage and the whole process of efficient memory management is called garbage collection.

The main objective of a garbage collector is to separate the dead objects from the live objects and reclaim the space for reuse. Basically, the whole thing works on managed heap, which is nothing but a memory block and the garbage collector periodically checks the heap memory to allocate memory to new objects. There are two methods to release unmanaged resources like files and database connections: Dispose and Finalize.

This article helps you understand the difference between the two.

What is a Dispose Method?

Dispose is a standard way for users to tell objects to release their resources and not to try to access the objects again. The dispose method provides control of explicit memory cleanup by rendering the objects unusable.

When the users calls the Dispose ( ) method, the object is supposed to free up all its expensive resources thereby making it available for reuse. It is never called by the garbage collector which only comes to play when managed memory becomes scarce. A special interface called “IDisposable” is used to decide where and how to implement Dispose ( ). But what happens when the dispose method does not get called?


What is a Finalize Method?

If dispose method does not get called, the fallback plan is to use Finalize ( ) method for cleanup. It is called by the garbage collector to perform a final resource cleanup before it frees memory. The concept of timely cleanup becomes inapplicable here because rather than de-allocating the memory immediately, the object is added to the finalization queue only to be destroyed later. Finalize is more like a safeguard put in place in the event of a programming error and the dispose does not clean up the resources in which case the Finalize ( ) method is called by the garbage collector to remove unreachable objects in whatever sequence it likes.


Difference between Dispose and Finalize

Basics of Dispose and Finalize

Dispose method is called to speed up the release of unmanaged resources such as database handles, file handles, semaphores, and other objects allocated by the operating system. The dispose method is invoked to execute code required to cleanup unused memory and scarce resources like GDI handles. In simple terms, dispose method provides control of explicit memory cleanup. Finalize method, on the other hand, is part of garbage collection used to perform final cleanup operation on an object before it’s being garbage collected. Simply put, finalize method is called to free unmanaged resources held by an object before it’s destroyed.

Invoking of Dispose and Finalize

Dispose method can be called explicitly by the user code and the class which is implementing the method to dispose resources. However, the memory cannot be released until the garbage collector performs the cleanup process. The method can be called even if other references to the object still exist. The finalize method, on the contrary, can be invoked by the garbage collector only after it determines that the last memory object instance is destroyed and no more references to the object exists. After the finalize method is executed, the object is removed from the heap memory.

Implementation of Dispose and Finalize

The process of disposing an object from the memory is called dispose pattern, which can be used for objects that access unmanaged resources because the garbage collector is unable to reclaim unmanaged resources. The “IDisposable” interface along with an additional Dispose (Boolean) method is implemented asking for the release of unmanaged resources. A finalize method is executed when instance of an object is destroyed prior to its deallocation. It is a non-deterministic method which occurs at the discretion of the garbage collector and may not even occur. It should not be implemented on managed objects until extremely necessary.

Performance of Dispose and Finalize

It’s much faster to use a dispose method rather than finalize for instant disposal of objects. Destructors are automatically converted to finalize method at runtime. It is automatically invoked by the garbage collector when the object goes out of the scope, which usually happens when the instance of that object is destroyed. The problem with finalize method is that it’s non-deterministic meaning it’s not certain when to reclaim memory that are no longer being referenced through garbage collection. However, it may not free memory immediately; in fact, it may never be called and it cannot be forced explicitly.

Dispose vs. Finalize: Comparison Chart


Summary of Dispose vs Finalize

The main difference between dispose and finalize methods is that the former is a deterministic method that instantly dispose objects when they are no longer in use, while the latter is a non-deterministic method for allocating unmanaged resources meaning it is a backstop method to free up memory object instances when they go out of scope prior to their deallocation. It is always advisable to use the dispose method over finalize unless extremely necessary.

In other terms, finalize is a safeguard put in place to clean up unmanaged resources when dispose method cannot be called in the event of some programming error. Finalize method is called by the garbage collector when an object is about to be kicked out of the heap memory.

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References :

[0]Lowy, Juval. Programming .NET Components. Sebastopol: O’Reilly Media, 2005. Print

[1]Burton, Kevin R. Net Common Language Runtime Unleashed. Indianapolis: Sams Publishing, 2002. Print

[2]Blair, Richard, et al. Beginning VB.Net. New Jersey: John Wiley & Sons, 2004. Print

[3]Image credit: https://upload.wikimedia.org/wikipedia/commons/d/da/UmbDotNetContols4.jpg

[4]Image credit: https://upload.wikimedia.org/wikipedia/commons/1/17/C_Sharp_Code.PNG

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