Circular Lists

As the name suggests, a circular list is cyclic. It may be singly-linked (as in the diagram) or doubly-linked, but there is neither a first node nor a last node:

[circular list]

You need something like LIST-P pointing somewhere in the list, but it needn't point to any node in particular. It might hop around the list in the course of processing.

For example, you might use a circular list to implement a simple round-robin scheduler. Each node would represent a task. The scheduler would give each task a slice of time and then move to the next. New tasks would be inserted, and old ones deleted, as they come and go.

Not many people write operating systems in COBOL, and it's hard to come up with a more plausible example. However, you might create a circular list by accident, and then find yourself in an infinite loop when you try to traverse it.

[home]COBOL Home [crane]Data Structures