Uniprocessor Garbage Collection Techniques

We survey basic garbage collection algorithms and variations such as incremental and gen erational collection The basic algorithms include reference counting mark sweep mark compact copy ing and treadmill collection Incremental techniques can keep garbage collection pause times short by interleaving small amounts of collection work with program execution Generational schemes improve e ciency and locality by garbage collecting a smaller area more often while exploiting typical lifetime characteristics to avoid undue overhead from long lived objects Automatic Storage Reclamation Garbage collection is the automatic reclamation of computer storage Knu Coh App While in many systems programmers must explicitly reclaim heap memory at some point in the program by using a free or dispose statement garbage collected systems free the programmer from this burden The garbage collector s function is to nd data objects that are no longer in use and make their space available for reuse by the the running program An object is considered garbage and subject to reclamation if it is not reachable by the running program via any path of pointer traversals Live potentially reachable objects are preserved by the collector ensuring that the program can never traverse a dangling pointer into a deallocated object This paper is intended to be an introductory survey of garbage collectors for uniprocessors especially those developed in the last decade For a more thorough treatment of older techniques see Knu Coh