SSP chains are a novel technique for referencing objects in a distributed system. To client software, any object reference appears to be a local pointer; when the target is remote, an SSP chain adds an indeterminate number of levels of indirection. Copying a reference across the distributed system extends an SSP chain at one end; migrating the target object extends it at the other end. Invocation through an SSP chain is efficient: each stage of an SSP chain contains location information and long chains are short-cut at invocation time. These actions require (almost) no extra messages in addition to those of the client application. The rules for creating, using, modifying and deleting SSP chains are stated precisely and maintain well-defined invariants. The invariants hold even in the presence of message failures (loss, duplication, late delivery); after a crash, the existence invariants must be re-established. SSP chains support distributed garbage collection (GC); we present a robust ...

This paper is organised as follows. Section 2 first introduces our object model. Section 3 describes the reference count-based approach. In particular, we compare those techniques according to their resilience to message failures. Such counting-based techniques are unable to collect cycles of garbage and must assume that they are rare enough to minimize memory leakage. A number of hybrid proposals as explained in 5 which combine counting-based techniques with a global (tracing-based) technique. Section (explained in Section 6) surveys some enhanced techniques well suited to distributed settings. Section (explained in Section 7) sums up our conclusions and proposes taxonomy of the reviewed techniques. 2 Model

GUM is a portable, parallel implementation of the Haskell functional language. Despite sustained research interest in parallel functional programming, GUM is one of the first such systems to be made publicly available. GUM is message-based, and portability is facilitated by using the PVM communications harness that is available on many multi-processors. As a result, GUM is available for both shared-memory (Sun SPARCserver multiprocessors) and distributed-memory (networks of workstations) architectures. The high message-latency of distributed machines is ameliorated by sending messages asynchronously, and by sending large packets of related data in each message. Initial performance figures demonstrate absolute speedups relative to the best sequential compiler technology. To improve the performance of a parallel Haskell program GUM provides tools for monitoring and visualising the behaviour of threads and of processors during execution.

In this report we present a fault-tolerant and efficient algorithm for distributed garbage collection and prove its correctness. The algorithm is a generalization of reference counting; it maintains a set of identifiers for processes with references to an object. The set is maintained with pair-wise communication between processes, so no global synchronization is required. The primary cost for maintaining the set is one remote procedure call when an object reference is transferred to a new process for the first time. The distributed collector collaborates with the local collector in detecting garbage; any local collector may be used, so long as it can be extended to provide notification when an object is collected. In fact, the distributed collector could be used without a local collector; in that case, the programmer would insert explicit dispose commands to release an object. The algorithm was designed and implemented as part of the Modula-3 network objects system, but it should be s...

It is shown that the termination detection problem for distributed computations can be modeled as an instance of the garbage collection problem. Consequently, algorithms for the termination detection problem are obtained by applying transformations to garbage collection algorithms. The transformation can be applied to collectors of the "mark--and--sweep" type as well as to reference counting garbage collectors. As examples, the scheme is used to transform the distributed reference counting protocol of Lermen and Maurer, the weighted reference counting protocol, the local reference counting protocol, and Ben--Ari's mark--and--sweep collector into termination detection algorithms. Known termination detection algorithms as well as new variants are obtained. Categories and Subject Descriptors: D.1.3 [Programming Techniques]: Concurrent Programming; C.2.4 [Computer--Communication Networks]: Distributed Systems---Network Operating Systems; D.4.2 [Operating Systems]: Storage Management--- D...

Distributed implementations of programming languages with implicit parallelism hold out the prospect that the parallel programs are immediately scalable. This paper presents some of the results of our part of Esprit 415, in which we considered the implementation of lazy functional programming languages on distributed architectures. A compiler and abstract machine were designed to achieve this goal. The abstract parallel machine was formally specified, using Miranda 1 . Each instruction of the abstract machine was then implemented as a macro in the Transputer Assembler. Although macro expansion of the code results in non-optimal code generation, use of the Miranda specification makes it possible to validate the compiler before the Transputer code is generated. The hardware currently available consists of five T800--25's, each board having 16M bytes of memory. Benchmark timings using this hardware are given. In spite of the straight forward code-generation, the resulting system compar...

This dissertation makes four contributions towards supporting distributed, multiuser applications over open networks. Dreme, a distributed dialect of the Scheme language in which all first-class language objects are mobile in the network. In particular, various distributed topologies, such as client/server and peer-to-peer, can be created by migrating closures with overlapping scopes around the network, correct inter-process communication being assured by Scheme's lexical scoping rules and network wide addressing. Threads of control are passed around through first-class distributed continuations. A User Interface toolkit for coordinating events in multi-threaded, multi-user applications by organizing continuation callbacks into nested lexical scopes. Each event has certain attributes, such as synchronous/asynchronous. Certain events create new scopes with new events. Continuation callbacks allow both synchronous events which return values to their callers, and asynchronous ones. Applic...

Weighted Reference Counting is a low communication distributed storage reclamation scheme for loosely-couple multiprocessors. The algorithm we present herein extends weighted reference counting to allow the collection of cyclic data structures. To do so, the algorithm identifies candidate objects that may be part of cycles and performs a tricolour mark-scan on their subgraph in a lazy manner to discover whether the subgraph is still in use. The algorithm is concurrent in the sense that multiple useful computation processes and garbage collection processes can be performed simultaneously. Keywords: Memory management, Distributed memory, Reference counting, Garbage collection. Introduction Computation on distributed systems involving several processors is already a reality. In a distributed multiprocessor system each processor is responsible for allocating and reclaiming structures residing in its local memory; interprocessor communication is far less efficient than local memory access...

. We present a distributed garbage collection algorithm that eventually collects all cycles in an open network. As with recent reference counting algorithms, it explicitly maintain the distributed inverse reference graph (i.e., each object maintains a list of sites known to have references to it). We show that a modified depth-first traversal of this inverse graph is sufficient to locate any garbage it contains. We also provide a heuristic to control the frequency of distributed collections. The inverse graph has other uses, such as maintaining distributed consistency, which makes it particularly useful in a network where cooperation is not assured. Keywords: Distributed Garbage Collection, Memory Management of Distributed Objects 1 Introduction Distributed cooperative applications on open public networks, such as the Internet, represent a new class of systems with unusual characteristics. In particular, the cooperating parties execute in different security domains, are written by dif...

This paper describes the design and implementation of a garbage collection scheme on large-scale distributed-memory computers and reports various experimental results. The collector is based on the conservative GC library by Boehm & Weiser. Each processor traces local pointers using the GC library while traversing remote pointers by exchanging "mark messages" between processors. It exhibits a promising performance---in the most space-intensive settings we tested, the total collection overhead ranges from 5% up to 15% of the application running time (excluding idle time). We not only examine basic performance figures such as the total overhead or latency of a global collection, but also demonstrate how local collection scheduling strategies affect application performance. In our collector, a local collection is scheduled either independently or synchronously. Experimental results show that the benefit of independent local collections has been overstated in the literature. Independent l...