Diff for Garbage collection (computer science)

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== Garbage collection (computer science) ==

'''Garbage collection''' (GC) is a form of automatic memory management in [[computer programming]]. It automatically reclaims memory that was previously allocated by a program but is no longer referenced, freeing it for reuse. Garbage collection relieves programmers from manual memory management tasks such as calling ''free'' or ''delete'', reducing errors like [[memory leak]]s, dangling pointers, and double frees. It is a key feature of many high-level languages including [[Java (programming language)|Java]], [[C Sharp (programming language)|C#]], [[Python (programming language)|Python]], and [[Go (programming language)|Go]].

== History ==

The concept of garbage collection originated in the 1950s with the [[Lisp (programming language)|Lisp]] language, developed by John McCarthy at MIT. The first implementation used a simple mark-and-sweep algorithm. In the following decades, researchers developed more sophisticated techniques such as [[reference counting]], copying collectors, and generational collection. The 1970s and 1980s saw theoretical advances like the Baker treadmill and the [[Boehm–Demers–Weiser garbage collector|Boehm collector]], which made GC practical for languages like [[C (programming language)|C]] and [[C++]]. Modern systems often combine multiple strategies to achieve low pause times and high throughput, as seen in the Java Virtual Machine and .NET runtime.

== Techniques ==

* '''[[Reference counting]]''' – Each object stores a count of references to it; when the count drops to zero, the object is immediately reclaimed. Simple but fails on cyclic references unless augmented with a cycle detector.
* '''[[Mark and sweep]]''' – A two-phase algorithm: first, the collector marks all reachable objects starting from roots (global variables, stack frames); second, it sweeps through memory and reclaims unmarked objects.
* '''[[Copying collector]]''' – Memory is divided into two semi-spaces; live objects are copied into an empty space, compacting them and leaving the old space as garbage. Used in [[Generational garbage collection|generational collectors]].
* '''[[Generational garbage collection|Generational collection]]''' – Exploits the observation that most objects die young. Objects are grouped by age; young objects are collected frequently (minor GC), while older objects are collected less often (major GC). This improves throughput.

== Advantages and disadvantages ==

Garbage collection increases programmer productivity by eliminating manual memory management and reducing bugs. It also enables safer [[memory safety|memory-safe]] languages. However, it can introduce unpredictable pauses (stop-the-world events) and overhead in CPU and memory, which may be unsuitable for [[real-time computing]] or systems with limited resources. Modern collectors use concurrent and incremental techniques to mitigate these issues.

== See also ==

* [[Automatic memory management]]
* [[Memory leak]]
* [[Tracing garbage collection]]
* [[Runtime system]]

[[Category:Memory management]]
[[Category:Programming language implementation]]
[[Category:Automatic memory management]]