15.3 Finalizers
When implementing your own
types, you can choose to give them
finalizers (by providing C# destructors). Finalizers are methods
called asynchronously by the GC once an object is determined to be
garbage.
Although this is required in certain cases, in general there are many
good technical reasons to avoid the use of finalizers.
As described in the previous section, objects with finalizers incur
significant overhead when they are collected, requiring asynchronous
invocation of their Finalize methods and taking
two full GC cycles for their memory to be reclaimed.
Other reasons not to use finalizers include:
Objects with finalizers take longer to allocate on the managed heap
than objects without finalizers. Objects with finalizers that refer to other objects (even those
without finalizers) can prolong the life of the referred objects
unnecessarily. It's impossible to predict in what order the
finalizers for a set of objects will be called. You have limited control over when (or even if!) the finalizer for an
object will be called.
In summary, finalizers are somewhat like lawyers梬hile there
are cases in which you really need them, in general you
don't want to use them unless absolutely necessary.
If you do use them, you need to be 100 percent sure you understand
what they are doing for you.
If you have to implement a finalizer, follow these guidelines or have
a very good reason for not doing so:
Ensure that your finalizer executes quickly. Never block in your finalizer. Free any unmanaged resources you own. Don't reference any other objects. Don't throw any unhandled exceptions.
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