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Cheney's algorithm

Cheney's algorithm, first described in a 1970 ACM paper by C.J. Cheney, is a stop and copy method of tracing garbage collection in computer software systems. In this scheme, the heap is divided into two equal halves, only one of which is in use at any one time. Garbage collection is performed by copying live objects from one semispace to the other, which then becomes the new heap. The entire old heap is then discarded in one piece. It is an improvement on the previous stop-and-copy technique.

Semispace
Cheney based his work on the semispace garbage collector, which was published a year earlier by R.R. Fenichel and J.C. Yochelson. == Equivalence to tri-color abstraction ==
Equivalence to tri-color abstraction
Cheney's algorithm is an example of a tri-color marking garbage collector. The first member of the gray set is the stack itself. Objects referenced on the stack are copied into the to-space, which contains members of the black and gray sets. The algorithm moves any white objects (equivalent to objects in the from-space without forwarding pointers) to the gray set by copying them to the to-space. Objects that are between the scanning pointer and the free-space pointer on the to-space area are members of the gray set still to be scanned. Objects below the scanning pointer belong to the black set. Objects are moved to the black set by simply moving the scanning pointer over them. When the scanning pointer reaches the free-space pointer, the gray set is empty, and the algorithm ends. == References ==
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