CS 330 Lecture 29 – Garbage Collection
April 16, 2012 by Chris Johnson. Filed under
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cs330, lectures, spring 2012.
Agenda
- how does polymorphism work?
- Jim Blinn’s terrible approach
- the elegant vtable approach
- garbage collection
- programmers don’t get explicit reclamation right
- OS does reclaim memory when program stops
- what happens when…
- … we don’t call free?
- … we call free twice?
- … we call free once but leave pointer untouched?
- some approaches:
- mark-and-sweep
- stop-and-copy
- reference counting
- a C++ counter pointer
- pair pointer with reference count
- maintain count on copy, assignment, destruction
- when count goes to 0, free it
TODO
Mark-and-sweep
for each allocated block:
mark unvisited
for each pointer on stack:
mark block pointed to visited
recurse on any pointers in block
for each allocated block:
free if block unvisited
Code
…
Haiku
Grades would be easy.
But you all have vtables.
You are dynamic.