Garbage Collection

Garbage collection is a method of automatically recycling storage that is no longer in use:

• If heap storage is available, return the next item of heap storage.

• Otherwise, perform a garbage collection to reclaim unused storage. If enough was collected, allocate the requested item and continue.

• Otherwise, request more memory from the operating system.

• Otherwise, fail due to lack of memory.

Garbage collection requires that the type of every piece of runtime memory be identifiable by the garbage collector, and that there are no possible errors in type determination. This may difficult for some languages, especially if the language allows variant records or pointer arithmetic. Garbage collection has been used in Lisp since about 1960; it is also used in Java.