Finalize vs Dispose

Question

Why do some people use the Finalize method over the Dispose method    In what situations would you use the Finalize method over the Dispose method and vice versa

User · Answer

As we know dispose and finalize both are used to free unmanaged resources   but the difference is finalize uses two cycle to free the resources   where as dispose uses one cycle

User · Answer

Others have already covered the difference between Dispose and Finalize  btw the Finalize method is still called a destructor in the language specification   so I ll just add a little about the scenarios where the Finalize method comes in handy   Some types encapsulate disposable resources in a manner where it is easy to use and dispose of them in a single action  The general usage is often like this  open  read or write  close  Dispose   It fits very well with the using construct   Others are a bit more difficult  WaitEventHandles for instances are not used like this as they are used to signal from one thread to another  The question then becomes who should call Dispose on these  As a safeguard types like these implement a Finalize method  which makes sure resources are disposed when the instance is no longer referenced by the application

User · Answer

The finalizer is for implicit cleanup - you should use this whenever a class manages resources that absolutely must be cleaned up as otherwise you would leak handles   memory etc     Correctly implementing a finalizer is notoriously difficult and should be avoided wherever possible - the SafeHandle class  avaialble in  Net v2 0 and above  now means that you very rarely  if ever  need to implement a finalizer any more   The IDisposable interface is for explicit cleanup and is much more commonly used - you should use this to allow users to explicitly release or cleanup resources whenever they have finished using an object   Note that if you have a finalizer then you should also implement the IDisposable interface to allow users to explicitly release those resources sooner than they would be if the object was garbage collected   See DG Update  Dispose  Finalization  and Resource Management for what I consider to be the best and most complete set of recommendations on finalizers and IDisposable

User · Answer

The main difference between Dispose and Finalize is that   Dispose is usually called by your code  The resources are freed instantly when you call it  People forget to call the method  so using      statement is invented  When your program finishes the execution of the code inside the     it will call Dispose method automatically    Finalize is not called by your code  It is mean to be called by the Garbage Collector  GC   That means the resource might be freed anytime in future whenever GC decides to do so  When GC does its work  it will go through many Finalize methods  If you have heavy logic in this  it will make the process slow  It may cause performance issues for your program  So be careful about what you put in there    I personally would write most of the destruction logic in Dispose  Hopefully  this clears up the confusion

User · Answer

The summary is -   You write a finalizer for your class if it has reference to unmanaged resources and you want to make sure that those unmanaged resources are released when an instance of that class is garbage collected automatically  Note that you can t call the Finalizer of an object explicitly - it s called automatically by the garbage collector as and when it deems necessary  On the other hand  you implement the IDisposable interface and consequently define the Dispose   method as a result for your class  when your class has reference to unmanaged resources  but you don t want to wait for the garbage collector to kick in  which can be anytime - not in control of the programmer  and want to release those resources as soon as you are done  Thus  you can explicitly release unmanaged resources by calling an object s Dispose   method    Also  another difference is - in the Dispose   implementation  you should release managed resources as well  whereas that should not be done in the Finalizer  This is because it s very likely that the managed resources referenced by the object have already been cleaned up before it s ready to be finalized   For a class that uses unmanaged resources  the best practice is to define both - the Dispose   method and the Finalizer - to be used as a fallback in case a developer forgets to explicitly dispose off the object  Both can use a shared method to clean up managed and unmanaged resources  -  class ClassWithDisposeAndFinalize   IDisposable          Used to determine if Dispose   has already been called  so that the finalizer        knows if it needs to clean up unmanaged resources       private bool disposed   false        public void Dispose                    Call our shared helper method            Specifying  true  signifies that the object user triggered the cleanup            CleanUp true              Now suppress finalization to make sure that the Finalize method            doesn t attempt to clean up unmanaged resources            GC SuppressFinalize this               private void CleanUp bool disposing                    Be sure we have not already been disposed          if   this disposed                            If disposing equals true i e  if disposed explicitly  dispose all                  managed resources              if  disposing                                Dispose managed resources                                Clean up unmanaged resources here                    disposed   true                    the below is called the destructor or Finalizer       ClassWithDisposeAndFinalize                     Call our shared helper method             Specifying  false  signifies that the GC triggered the cleanup          CleanUp false

User · Answer

Finalize is the backstop method  called by the garbage collector when it reclaims an object   Dispose is the  deterministic cleanup  method  called by applications to release valuable native resources  window handles  database connections  etc   when they are no longer needed  rather than leaving them held indefinitely until the GC gets round to the object   As the user of an object  you always use Dispose   Finalize is for the GC   As the implementer of a class  if you hold managed resources that ought to be disposed  you implement Dispose   If you hold native resources  you implement both Dispose and Finalize  and both call a common method that releases the native resources   These idioms are typically combined through a private Dispose bool disposing  method  which Dispose calls with true  and Finalize calls with false   This method always frees native resources  then checks the disposing parameter  and if it is true it disposes managed resources and calls GC SuppressFinalize

User · Answer

Class instances often encapsulate control over resources that are not managed by the runtime  such as window handles  HWND   database connections  and so on  Therefore  you should provide both an explicit and an implicit way to free those resources  Provide implicit control by implementing the protected Finalize Method on an object  destructor syntax in C  and the Managed Extensions for C     The garbage collector calls this method at some point after there are no longer any valid references to the object  In some cases  you might want to provide programmers using an object with the ability to explicitly release these external resources before the garbage collector frees the object  If an external resource is scarce or expensive  better performance can be achieved if the programmer explicitly releases resources when they are no longer being used  To provide explicit control  implement the Dispose method provided by the IDisposable Interface  The consumer of the object should call this method when it is done using the object  Dispose can be called even if other references to the object are alive   Note that even when you provide explicit control by way of Dispose  you should provide implicit cleanup using the Finalize method  Finalize provides a backup to prevent resources from permanently leaking if the programmer fails to call Dispose

User · Answer

Finalize   Finalizers should always be protected  not public or private so that the method cannot be called from the application s code directly and at the same time  it can make a call to the base Finalize method Finalizers should release unmanaged resources only  The framework does not guarantee that a finalizer will execute at all on any given instance  Never allocate memory in finalizers or call virtual methods from finalizers  Avoid synchronization and raising unhandled exceptions in the finalizers  The execution order of finalizers is non-deterministic   in other words  you can t rely on another object still being available within your finalizer  Do not define finalizers on value types  Don t create empty destructors  In other words  you should never explicitly define a destructor unless your class needs to clean up unmanaged resources and if you do define one  it should do some work  If  later  you no longer need to clean up unmanaged resources in the destructor  remove it altogether    Dispose   Implement IDisposable on every type that has a finalizer Ensure that an object is made unusable after making a call to the Dispose method  In other words  avoid using an object after the Dispose method has been called on it  Call Dispose on all IDisposable types once you are done with them Allow Dispose to be called multiple times without raising errors  Suppress later calls to the finalizer from within the Dispose method using the GC SuppressFinalize method Avoid creating disposable value types Avoid throwing exceptions from within Dispose methods   Dispose Finalized Pattern   Microsoft recommends that you implement both Dispose and Finalize when working with unmanaged resources  The Finalize implementation would run and the resources would still be released when the object is garbage collected even if a developer neglected to call the Dispose method explicitly  Cleanup the unmanaged resources in the Finalize method as well as Dispose method  Additionally call the Dispose method for any  NET objects that you have as components inside that class having unmanaged resources as their member  from the Dispose method

User · Answer

99  of the time  you should not have to worry about either      But  if your objects hold references to non-managed resources  window handles  file handles  for example   you need to provide a way for your managed object to release those resources   Finalize gives implicit control over releasing resources   It is called by the garbage collector   Dispose is a way to give explicit control over a release of resources and can be called directly   There is much much more to learn about the subject of Garbage Collection  but that s a start

User · Answer

To answer on the first part you should provide examples where people use  different approach for the exact same class-object   Otherwise it is difficult  or even strange  to answer   As for the second question better read first this Proper use of the IDisposable interface which claims that      It s your choice  But choose Dispose    In other words  The GC only knows about finalizer  if any  Also known as destructor to Microsoft   A good code will attempt to cleanup from both  finalizer and Dispose

User · Answer

The best example which i know    public abstract class DisposableType  IDisposable         bool disposed   false        DisposableType               if   disposed                   disposed   true          Dispose false                      public void Dispose               if   disposed                   disposed   true          Dispose true           GC SuppressFinalize this                      public void Close               Dispose               protected virtual void Dispose bool disposing              if  disposing                      managed objects                  unmanaged objects and resources

User · Answer

Diff between Finalize and Dispose methods in C    GC calls the finalize method to reclaim the unmanaged resources such as file operarion  windows api  network connection  database connection  but time is not fixed when GC would call it  It is called implicitly by GC it means we do not have low level control on it   Dispose Method  We have low level control on it as we call it from the code  we can reclaim the unmanaged resources whenever we feel it is not usable We can achieve this by implementing IDisposal pattern

User · Answer

Finalize gets called by the GC when this object is no longer in use   Dispose is just a normal method which the user of this class can call to release any resources   If user forgot to call Dispose and if the class have Finalize implemented then GC will make sure it gets called

User · Answer

The finalizer method is called when your object is garbage collected and you have no guarantee when this will happen  you can force it  but it will hurt performance    The Dispose method on the other hand is meant to be called by the code that created your class so that you can clean up and release any resources you have acquired  unmanaged data  database connections  file handles  etc  the moment the code is done with your object   The standard practice is to implement IDisposable and Dispose so that you can use your object in a using statment  Such as using var foo   new MyObject         And in your finalizer  you call Dispose  just in case the calling code forgot to dispose of you

User · Answer

There re some keys about from the book MCSD Certification Toolkit  exam 70-483  pag 193   destructor    it s almost equal to  base Finalize    The destructor is converted into an override version of the Finalize method that executes the destructor   s code and then calls the base class   s Finalize method  Then its totally non deterministic you can t able to know when will be called because depends on GC   If a class contains no managed resources and no unmanaged resources  it shouldn t implement IDisposable or have a destructor   If the class has only managed resources  it should implement IDisposable but it shouldn t have a destructor   When the destructor executes  you can   t be sure managed objects still  exist  so you can   t call their Dispose   methods anyway    If the class has only unmanaged resources  it needs to implement IDisposable and needs a destructor in case the program doesn   t call Dispose     Dispose   method must be safe to run more than once  You can achieve that by using a variable to keep track of whether it has been run before   Dispose   should free both managed and unmanaged resources    The destructor should free only unmanaged resources  When the destructor executes  you  can   t be sure managed objects still exist  so you can   t call their Dispose methods anyway  This is obtained by using the canonical protected void Dispose bool disposing  pattern  where only managed resources are freed  disposed  when disposing    true    After freeing resources  Dispose   should call GC SuppressFinalize  so the object can  skip the finalization queue   An Example of a an implementation for a class with unmanaged and managed resources   using System   class DisposableClass   IDisposable          A name to keep track of the object      public string Name               Free managed and unmanaged resources      public void Dispose                 FreeResources true               We don t need the destructor because            our resources are already freed          GC SuppressFinalize this                 Destructor to clean up unmanaged resources        but not managed resources       DisposableClass                 FreeResources false                 Keep track if whether resources are already freed      private bool ResourcesAreFreed   false          Free resources      private void FreeResources bool freeManagedResources                Console WriteLine Name      FreeResources            if   ResourcesAreFreed                           Dispose of managed resources if appropriate              if  freeManagedResources                                   Dispose of managed resources here                  Console WriteLine Name      Dispose of managed resources                                  Dispose of unmanaged resources here              Console WriteLine Name      Dispose of unmanaged resources                    Remember that we have disposed of resources              ResourcesAreFreed   true

[c#] Finalize vs Dispose

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