Garbage collection: Difference between revisions

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Garbage collection (often abbreviated as GC) is a technique used for management of the life cycle of the objects created dynamically, which scope is statically indeterminable. Sometimes GC is called "automatic memory management". Under GC the objects that are no longer in use by the program are said to be "collected." The object is finalized and then the memory allocated for it is returned to the language environment for further reuse. An object is considered not in use when there is no legal way to access it. In particular, when there are no other accessible objects referencing it. Many GC algorithms differentiate in the way they determine absence of references.

Some programming languages (such as Java, Tcl, OCaml, and Toka) have an integrated GC support. Languages like Ada allow implementations with GC, but don't mandate it. Languages like Phix use reference counting, so memory is collected immediately rather than periodically. Other languages (such as C and C++) do not have GC.

GC is frequently critiqued for:

unpredictable performance both in terms of time and space;
distributed overhead for multi-tasking systems;
difficulties in ensuring a proper finalization of collected objects;
encouraging loose program design.

GC is a very vivid research area in computer science, focused on overwhelming the above mentioned drawbacks.

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+[[Category:Encyclopedia]]'''Garbage collection''' (often abbreviated as '''GC''') is a technique used for management of the life cycle of the objects created [[run time|dynamically]], which scope is [[compile time|statically]] indeterminable. Sometimes GC is called "automatic memory management". Under GC the objects that are no longer in use by the program are said to be "collected." The object is finalized and then the memory allocated for it is returned to the language environment for further reuse. An object is considered not in use when there is no legal way to access it. In particular, when there are no other accessible objects [[reference|referencing]] it. Many GC algorithms differentiate in the way they determine absence of references.
-[[Category:Encyclopedia]]'''Garbage collection''' (sometimes called "automatic memory management") is a feature of some [[programming language|programming languages]] (such as [[Java]], [[Tcl]], and [[Toka]]) which manages memory allocation so that memory locations that are no longer in use by the program are "given back" to the [[OS|operating system]].
+Some [[programming language|programming languages]] (such as [[Java]], [[Tcl]], [[OCaml]], and [[Toka]]) have an integrated GC support. Languages like [[Ada]] allow implementations with GC, but don't mandate it. Languages like [[Phix]] use reference counting, so memory is collected immediately rather than periodically. Other languages (such as [[C]] and [[C++]]) do not have GC.
-A memory location is no longer in use when there are no [[reference|references]] to it in use anymore. For instance (in a language with scope):
- for i = 1 to 10
-   var x = i * i
-   print "x is in scope since it was declared in this for block"
- end for
- print "x is no longer in scope and its memory location should now be given back to the OS"
+GC is frequently critiqued for:
-Some languages (such as [[C]] and [[C++]]) do not have garbage collection and the programmer must do it himself.
+* unpredictable performance both in terms of time and space;
+* distributed overhead for [[task|multi-tasking]] systems;
+* difficulties in ensuring a proper finalization of collected objects;
+* encouraging loose program design.
+GC is a very vivid research area in computer science, focused on overwhelming the above mentioned drawbacks.