Finalizer

For the video game, see Finalizer (video game).
For the process related to optical disc media, see Finalize (optical discs).

In computer science, a finalizer or finalize method is a special method that performs finalization, generally some form of cleanup. A finalizer is executed during object destruction, prior to the object being deallocated, and is complementary to an initializer, which is executed during object creation, following allocation. Finalizers are strongly discouraged by some, due to difficulty in proper use and the complexity they add, and alternatives are suggested instead, mainly the dispose pattern[1] (see problems with finalizers).

The term finalizer is mostly used in object-oriented and functional programming languages that use garbage collection, of which the archetype is Smalltalk. This is contrasted with a destructor, which is a method called for finalization in languages with deterministic object lifetimes, archetypically C++.[2][3] These are generally exclusive: a language will have either finalizers (if automatically garbage collected) or destructors (if manually memory managed), but in rare cases a language may have both, as in C++/CLI and D, and in case of reference counting (instead of tracing garbage collection), terminology varies. In technical use, finalizer may also be used to refer to destructors, as these also perform finalization, and some subtler distinctions are drawn – see terminology. The term final also indicates a class that cannot be inherited; this is unrelated.

  1. ^ Jagger, Perry & Sestoft 2007, p. 542, "In C++, a destructor is called in a determinate manner, whereas, in C#, a finalizer is not. To get determinate behavior from C#, one should use Dispose.
  2. ^ Boehm, Hans-J. (2002). Destructors, Finalizers, and Synchronization. Symposium on Principles of Programming Languages (POPL).
  3. ^ Jagger, Perry & Sestoft 2007, p. 542, C++ destructors versus C# finalizers C++ destructors are determinate in the sense that they are run at known points in time, in a known order, and from a known thread. They are thus semantically very different from C# finalizers, which are run at unknown points in time, in an unknown order, from an unknown thread, and at the discretion of the garbage collector.