from
The Free On-line Dictionary of Computing (8 July 2008)
garbage collection
garbage collect
<programming> (GC) The process by which dynamically allocated
storage is reclaimed during the execution of a program. The
term usually refers to automatic periodic storage reclamation
by the garbage collector (part of the {run-time system}), as
opposed to explicit code to free specific blocks of memory.
Automatic garbage collection is usually triggered during
memory allocation when the amount free memory falls below some
threshold or after a certain number of allocations. Normal
execution is suspended and the garbage collector is run.
There are many variations on this basic scheme.
Languages like {Lisp} represent expressions as {graphs} built
from {cells} which contain pointers and data. These languages
use automatic {dynamic storage allocation} to build
expressions. During the evaluation of an expression it is
necessary to reclaim space which is used by subexpressions but
which is no longer pointed to by anything. This reclaimed
memory is returned to the free memory pool for subsequent
reallocation.
Without garbage collection the program's memory requirements
would increase monotonically throughout execution, possibly
exceeding 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.
(1997-08-25)