garbage collection

[′gär·bij kə‚lek·shən] (computer science) In a computer program with dynamic storage allocation, the automatic process of identifying those memory cells whose contents are no longer useful for the computation in progress and then making them available for some other use.

garbage collection

(programming)(GC) The process by which dynamically allocatedstorage is reclaimed during the execution of a program. Theterm usually refers to automatic periodic storage reclamationby the garbage collector (part of the run-time system), asopposed to explicit code to free specific blocks of memory.

Automatic garbage collection is usually triggered duringmemory allocation when the amount free memory falls below somethreshold or after a certain number of allocations. Normalexecution is suspended and the garbage collector is run.There are many variations on this basic scheme.

Languages like Lisp represent expressions as graphs builtfrom cells which contain pointers and data. These languagesuse automatic dynamic storage allocation to buildexpressions. During the evaluation of an expression it isnecessary to reclaim space which is used by subexpressions butwhich is no longer pointed to by anything. This reclaimedmemory is returned to the free memory pool for subsequentreallocation.

Without garbage collection the program's memory requirementswould increase monotonically throughout execution, possiblyexceeding system limits on virtual memory size.

The three main methods are mark-sweep garbage collection,reference counting and copying garbage collection.

See also the AI koan about garbage collection.

garbage collection

(1) Garbage collection is a function of an operating system or programming language that reclaims memory no longer in use. For example, Java and .NET have built-in garbage collection, but C and C++ do not, and programmers have to write the code to allocate and deallocate, which is tedious and error prone. See dynamic memory allocation and memory allocation.

(2) In a flash memory-based solid state drive (SSD), the garbage collection function improves write speed by erasing blocks of unused storage in the background. Flash memory requires blocks to be erased before they can be written, and having empty blocks available saves time when writing new data on the drive. See TRIM support, flash memory and SSD.

garbage collection