Finalization occurs when a garbage collector informs an application that an object is "almost collectable." It is used to help an application maintain its invariants. To make finalization more useful, this paper defines "almost collectable" in terms of a new class of objects, called ephemerons. Ephemerons are similar to weak pairs, but an object in an ephemeron's key field may be classed as "almost collectable" even if it is reachable from the epehemeron's value fields.

An approach to heterogeneous process migration that involves building a machine-independent migration program that specifies the current code and data state of the process to be migrated is described. When this program is compiled and executed on the target machine, it will first reconstruct the process's state and then continue the normal execution of the now-migrated process. The principal advantage of this approach is that it hides the details of code and data translation in the compilers for each machine.>

Object allocationand deallocation data gathered for the Cedar system on Xerox Dorados supports the weak generational hypothesis!newly-created objects have a much lower survival rate than objects that are older.The survivors at all collections thresholds are highly organized; large clusters of objects are allocated at roughly the same time, and live for roughly the same length of time.By cleverly selecting representatives from the clusters and examining the reachability of these key objects more frequently than the cluster itself, the storage system can use the death of these key objects to find good opportunities to collect the clusters they represent.

Two key ideas in garbage collection are generational collection and conservative pointer-finding. Generational collection and conservative pointer-finding are hard to use together, because generational collection is usually expressed in terms of copying objects, while conservative pointer-finding precludes copying. We present a new framework for defining garbage collectors. When applied to generational collection, it generalizes the notion of younger/older to a partial order. It can describe traditional generational and conservative techniques, and lends itself to combining different techniques in novel ways. We study in particular two new garbage collectors inspired by this framework. Both these collectors use conservative pointer-finding. The first one is based on a rewrite of an existing trace-and-sweep collector to use one level of generation. The second one has a single parameter, which controls how objects are partitioned into generations: the value of this parameter can be changed dynamically with no overhead. We have implemented both collectors and present measurements of their performance in practice.