Abstract. We present a denotational semantics based on action traces, for parallel programs which share mutable data and synchronize using resources and conditional critical regions. We introduce a resource-sensitive logic for partial correctness, adapting separation logic to the concurrent setting, as proposed by O’Hearn. The logic allows program proofs in which “ownership ” of a piece of state is deemed to transfer dynamically between processes and resources. We prove soundness of this logic, using a novel “local ” interpretation of traces, and we show that every provable program is race-free. 1

We introduce Guava, a dialect of Java whose rules statically guarantee that parallel threads access shared data only through synchronized methods. Our dialect distinguishes three categories of classes: (1) monitors, which may be referenced from multiple threads, but whose methods are accessed serially; (2) values, which cannot be referenced and therefore are never shared; and (3) objects, which can have multiple references but only from within one thread, and therefore do not need to be synchronized. Guava circumvents the problems associated with today's Java memory model, which must define behavior when concurrent threads access shared memory without synchronization.

Abstract: The author examines the synchronization features of Java and finds that they are insecure variants of his earliest ideas in parallel programming published in 1972-73. The claim that Java supports monitors is shown to be false. The author concludes that Java ignores the last twenty-five years of research in parallel programming languages. Zeywords: programming languages; parallel programming; monitors; security; Java; We must expect posterity to view with some asperity the marvels and the wonders we're passing on to it; but it should change its attitude to one of heartfelt gratitude when thinking of the blunders we didn't quite commit. 1. PLATFORM-INDEPENDENT PARALLEL PROGRAMMING Pier Hein (1966) Java has resurrected the well-known idea of platform-independent parallel program-ming. In this paper I examine the synchronization features of Java to discover their origin and determine if they live up to the standards set by the invention of monitors and Concurrent Pascal a quarter of a century ago. In the 1970s my students and I demonstrated that it is possible to write nontriv-ial parallel programs exclusively in a secure language that supports monitors. The milestones of this work were: • The idea of associating explicit queues with monitors [Brinch Hansen 1972]. • A class notation for monitors [Brinch Hansen 1973]. • A monitor language, Concurrent Pascal [Brinch Hansen 1975a]. • A portable compiler that generated platform-independent parallel code [Hart-mann 1975]. • A portable interpreter that ran platform-independent parallel code on a wide variety of computers [Brinch Hansen 1975b].

A language concept for concurrent processes without common variables is introduced. These processes communicate and synchronize by means of procedure calls and guarded regions. This concept is proposed for real-time applications controlled by microcomputer networks with distributed storage. The paper gives several examples of distributed processes and shows that they include

Orca is a language for programming parallel applications on distributed computing systems. Although processors in such systems communicate only through message passing and not through shared memory, data types and create instances (objects) of these types, which may be shared among processes. All operations on shared objects are executed atomically. Orca’s shared objects are implemented by replicating them in the local memories of the proces-sors. Read operations use the local copies of the object, without doing any interprocess communication. Write operations update all copies using an efficient reliable broadcast protocol. In this paper, we briefly describe the language and its implementation and then report on our ex-periences in using Orca for three parallel applications: the Traveling Salesman Problem, the All-pairs Shortest Paths problem, and Successive Overrelaxation. These applications have different needs for shared data: TSP greatly benefits from the support for shared data; ASP benefits from the use of broad-cast communication, even though it is hidden in the implementation; SOR merely requires point-to-point communication, but still can be implemented in the language by simulating message passing.

ion : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 30 3.1.3 Inheritance and Subclassing : : : : : : : : : : : : : : : : : : : : : : : : : : 32 3.1.4 Polymorphism : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 33 3.2 Definitions : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.1 Object-Oriented Language : : : : : : : : : : : : : : : : : : : : : : : : : : : 36 3.2.2 Object-Oriented System : : : : : : : : : : : : : : : : : : : : : : : : : : : : 37 3.3 Summary : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 38 4 Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : : : : : : : : 40 4.1 Definition of an Object-Oriented Operating System : : : : : : : : : : : : : : : : : 40 4.2 Advantages of Object-Oriented Operating Systems : : : : : : : : : : : : : : : : : 43 4.2.1 Portability Advantages : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 43 4.2.2 Code Sharing Adv...

Existing memory models and cache consistency protocols assume the memory coherence property which requires that all processors observe the same ordering of write operations to the same location. In this paper, we address the problem of defining a memory model that does not rely on the memory coherence assumption, and also the problem of designing a cache consistency protocol based on such a memory model. We define a new memory consistency model, called Location Consistency (LC), in which the state of a memory location is modeled as a partially ordered multiset (pomset) of write and synchronization operations. We prove that LC is strictly weaker than existing memory models, but is still equivalent to stronger models for parallel programs that have no data races. We also introduce a new multiprocessor cache consistency protocol based on the LC memory model. We prove that this LC protocol obeys the LC memory model. The LC protocol does not need to enforce single write ownership of memory...

We present a simple model of shared data-objects, which extends the abstract data type model to support distributed programming. Our model essentially provides shared address space semantics, rather than message passing semantics, without requiring physical shared memory to be present in the target system. We also propose a new programming language, Orca, based on shared dataobjects. A compiler and three different run time systems for Orca exist, which have been in use for over a year now.

pSather is a parallel extension of the existing object-oriented language Sather. It offers a shared-memory programming model which integrates both control- and dataparallel extensions. This integration increases the flexibility of the language to express different algorithms and data structures, especially on distributed-memory machines (e.g. CM-5). This report describes our design objectives and the programming language pSather in detail. ICSI and Eidgenossische Technische Hochschule (ETH), Zurich, Switzerland. E-mail: murer@icsi.berkeley.edu. y ICSI and Computer Science Division, U.C. Berkeley. E-mail: jfeldman@icsi.berkeley.edu. z ICSI and Computer Science Division, U.C. Berkeley. E-mail: clim@icsi.berkeley.edu. x ICSI E-mail: mseidel@icsi.berkeley.edu. ii Contents 1 Introduction 4 1.1 Roadmap of this Report : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 5 1.2 Grammar Notation : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 6 2...

data types Inheritance Object-based concurrency 1.