A Compiler Algorithm for Managing Asynchronous Memory Read Completion

Computers with conventional memory systems have a predictable latency between initiation and completion of a memory read. On such machines it is relatively easy for either the compiler or the processor to guarantee that a load has completed before further references to the loaded register are made. In a machine with a logically shared, but physically distributed, memory, these latencies are not statically predictable. Some existing systems, such as the Cray T3D, deal with this problem by using a hardware mechanism to enforce synchronization on a register which is the target of a remote memory access. The M-Machine currently being designed by the Concurrent VLSI Architecture Group at MIT performs remote memory accesses asynchronously, and allows program execution to continue while the access is outstanding, but does not enforce synchronization in hardware. This architectural simplification, and resulting relaxation of memory completion semantics, poses a challenge to the compiler: how can this simpler memory system be efficiently supported while maintaining program correctness. In particular, what is required to guarantee that there are no conflicts between completion of a memory operation by placing a value into a register, and other uses of the register being written. This paper describes a general solution to this problem, develops an algorithm to implement it, and shows that the algorithm is correct

A Message-Driven Programming System for Fine-Grain Multicomputers

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Modular circle quotients and PL limit sets

We say that a collection Gamma of geodesics in the hyperbolic plane H^2 is a modular pattern if Gamma is invariant under the modular group PSL_2(Z), if there are only finitely many PSL_2(Z)-equivalence classes of geodesics in Gamma, and if each geodesic in Gamma is stabilized by an infinite order subgroup of PSL_2(Z). For instance, any finite union of closed geodesics on the modular orbifold H^2/PSL_2(Z) lifts to a modular pattern. Let S^1 be the ideal boundary of H^2. Given two points p,q in S^1 we write pq if p and q are the endpoints of a geodesic in Gamma. (In particular pp.) We show that is an equivalence relation. We let Q_Gamma=S^1/ be the quotient space. We call Q_Gamma a modular circle quotient. In this paper we will give a sense of what modular circle quotients `look like' by realizing them as limit sets of piecewise-linear group actionsComment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol8/paper1.abs.htm

Teichmuller geodesics that do not have a limit in PMF

We construct a Teichmuller geodesic which does not have a limit on the Thurston boundary of the Teichmuller space.Comment: published versio

Experiences in Programming the J-Machine

This document summarizes experiences gained in programming the J-Machine. It is intended to provide feedback on the strengths and weaknesses of the architecture. The intent of this document is to provide useful information to system architects to assist in the design of the next generation of fine-grained multicomputers

Algebraic invariants, mutation, and commensurability of link complements

We construct a family of hyperbolic link complements by gluing tangles along totally geodesic four-punctured spheres, then investigate the commensurability relation among its members. Those with different volume are incommensurable, distinguished by their scissors congruence classes. Mutation produces arbitrarily large finite subfamilies of nonisometric manifolds with the same volume and scissors congruence class. Depending on the choice of mutation, these manifolds may be commensurable or incommensurable, distinguished in the latter case by cusp parameters. All have trace field Q(i,\sqrt{2}), but some have integral traces while others do not.Comment: Minor changes following referee's suggestion

Exemplary Teachers' Influence on Their Adolescent Pupils Who Later Became Teachers

There are many possible sources that may influence teachers in the acquisition of professional knowledge and skills throughout their careers. The current study analyzes 26 interviews with Israeli female teachers who reported on exemplary teachers from their past who served as role models regarding class management. Contrary to our initial assumption, the respondents of this study could recall only one or two outstanding teachers, mostly from middle and high school, from among the many teachers who had taught them in the past. The findings present outstanding professionals, those who possess unique and unusual personal and professional qualities in the inter-personal, professional and moral-social dimensions. The discussion analyzes how classroom management practices are recalled and why most of the key teachers appeared early in the lives of the respondents, long before they chose to become teachers and attend teachers colleges