We survey basic garbage collection algorithms, and variations such as incremental and generational collection; we then discuss low-level implementation considerations and the relationships between storage management systems, languages, and compilers. Throughout, we attempt to present a uni ed view based on abstract traversal strategies, addressing issues of conservatism, opportunism, and immediacy of reclamation; we also point outavariety of implementation details that are likely to have a significant impact on performance.

this paper. associated with a relocating collector is saved; other costs remain, however, such as the costs of updating all pointers and foregoing some compiler optimizations.

Hardware-assisted real-time garbage collection offers high throughput and small worst-case bounds on the times required to allocate dynamic objects and to access the memory contained within previously allocated objects. Whether the proposed technology is cost effective depends on various choices between configuration alternatives. This paper reports the performance of several different configurations of the hardware-assisted real-time garbage collection system subjected to several different workloads. Reported measurements demonstrate that hardware-assisted real-time garbage collection is a viable alternative to traditional explicit memory management techniques, even for low-level languages like C++.

We have implemented the first copying garbage collector that permits continuous unimpeded mutator access to the original objects during copying. The garbage collector incrementally replicates all accessible objects and uses a mutation log to bring the replicas up-to-date with changes made by the mutator. An experimental implementation demonstrates that the costs of using our algorithm are small and that bounded pause times of 50 milliseconds can be readily achieved. Keywords: real-time garbage collection, copying garbage collection, incremental collection, concurrent collection, replication. 1 Introduction Garbage collector pauses are always annoying, but for many applications they are intolerable. For example, smoothly Authors' addresses: nettles@cs.cmu.edu, School of Computer Science, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213. (412)268-3617 otoole@lcs.mit.edu, Laboratory for Computer Science, Massachusetts Institute of Technology, Cambridge, Ma...

ion helps programmers, including real-time programmers, deal with complexity. But real-time developers must use abstraction with discretion. They must be What is Real-Time Java? 10 Issues in the Design and Implementation of Real-Time Java able to break through layers of abstraction whenever this is necessary in order to understand or exercise control over real-time behavior. A Real-Time Java program consists of an arbitrary number of real-time activities accompanied by an arbitrary number of runnable threads. The runnable threads have no time-constrained behavior. The discussion of real-time activities provided below makes frequent reference the the real-time executive. See "The Real-Time Executive" on page 15. A Real-Time Activity A real-time activity consists of a configuration manager, an administrator, an arbitrary number of real-time tasks, and an arbitrary number of runnable threads. The point in specifying runnable threads as part of a real-time activity is to allow them to b...

Garbage collection is the automatic reclamation of computer storage [Knu73, Coh81, Wil92, Wil95]. While in many systems, programmers must explicitly reclaim heap memory at some point in their program by using a "free" or "dispose" statement, garbage collected systems free the programmer from this burden. In spite of its obvious attractiveness for many applications, garbage collection for real-time programs is not popular. This is largely due to the perceived cost and disruptiveness of garbage collection in general, and of incremental garbage collection in particular. Most existing "real-time" garbage collectors are not in fact usefully real-time, largely due to the use of a read barrier to trigger incremental copying of data structures being traversed by the running application. This may slow down running applications unpredictably, even though individual increments of garbage collection work are small and bounded. We have developed a hard real-time garbage collector which us...

this paper.

The Real-time Specification for Java extends the Java platform

This paper shows how to make the latency of scanning a page in the Appel-Ellis-Li real-time garbage collector be proportional only to the number of object references on a page (the page size), instead of to the sum of the sizes of the objects referenced by the page. This makes the garbage collection algorithm much more suitable for real-time systems.

We have implemented the first copying garbage collector that permits continuous unimpeded mutator access to the original objects during copying. The garbage collector incrementally replicates all accessible objects and uses a mutation log to bring the replicas up-to-date with changes made by the mutator. An experimental implementation demonstrates that the costs of using our algorithm are small and that bounded pause times of 50 milliseconds can be readily achieved.