SRC Research Report 63
SRC Research Report 63
Topaz, the experimental computing environment built and used at SRC, is implemented in the Modula-2+ programming language, which provides garbage collection. Garbage collection simplifies the construction of complex systems, and is tied to a number of other Topaz and Modula-2+ features, such as runtime polymorphism, language safety, information-hiding, object cleanup, persistent objects, and network objects.
Although there are costs to using garbage collection, these are avoided or tolerated in Topaz. For example, because Topaz must avoid noticeable interruption of service due to garbage collection, it uses a concurrent garbage collector.
Measurements show that the use of the REF heap in Topaz is similar in many ways to the use of heaps in Lisp-like environments, but different in others. For example, in typical large programs, the REF heap contains millions of bytes, with tens of thousands of objects from among hundreds of statically-declared types; objects of only a few types predominate. Although most objects are small, most bytes are in relatively large objects. Cycles are rare; most cycles are of size 2. Most objects are short-lived, but not as short-lived as in Lisp-like environments that allocate large amounts of ephemeral data on the heap.
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