Continuations in the Java Virtual Machine

Continuations have received considerable attention lately as a possible solution to web application development. Other uses proposed in the past, such as cooperative threading, coroutines or writing iterators, made them an attractive feature of dynamically typed languages. We present issues involved in adding continuations to a statically typed, object-oriented language like Java, and its implementation in the Java Virtual Machine. We propose three different flavors of continuations, and study their interactions with the base language, focusing on Java's concurrency model. We describe our implementation in Ovm, a realtime Java Virtual Machine, and discuss open issues

Use of preemptive program services with optimised native code

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A new approach to real-time checkpointing

The progress towards programming methodologies that simplify the work of the programmer involves automating, whenever possible, activities that are secondary to the main task of designing algorithms and developing applications. Automatic memory management, using garbage collection, and automatic persistence, using checkpointing, are both examples of mechanisms that operate behind the scenes, simplifying the work of the programmer. Implementing such mechanisms in the presence of real-time constraints, however, is particularly difficult. In this paper we review the behavior of traditional copy-onwrite implementations of checkpointing in the context of real-time systems, and we show how such implementations may, in pathological cases, seriously impair the ability of the user code to meet its deadlines. We discuss the source of the problem, supply benchmarks, and discuss possible remedies. We subsequently propose a novel approach that does not rely on copy-on-write and that, while more expensive in terms of CPU time overhead, is unaffected by pathological user code. We also describe our implementation of the proposed solution, based on the Ovm RTSJ Java Virtual Machine, and we discuss our experimental results

Accurate garbage collection in uncooperative environments revisited

Implementing a concurrent programming language such as Java by means of a translator to an existing language is attractive as it provides portability over all platforms supported by the host language and reduces development time - as many low-level tasks can be delegated to the host compiler. The C and C++ programming languages are popular choices for many language implementations due to the availability of efficient compilers on a wide range of platforms. For garbage-collected languages, however, they are not a perfect match as no support is provided for accurately discovering pointers to heap-allocated data on thread stacks. We evaluate several previously published techniques and propose a new mechanism, lazy pointer stacks, for performing accurate garbage collection in such uncooperative environments. We implemented the new technique in the Ovm Java virtual machine with our own Java-to-C/C++ compiler using GCC as a back-end compiler. Our extensive experimental results confirm that lazy pointer stacks outperform existing approaches: we provide a speedup of 4.5 over Henderson's accurate collector with a 17 increase in code size. Accurate collection is essential in the context of real-time systems, we thus validate our approach with the implementation of a real-time concurrent garbage collection algorithm

Accurate Garbage Collection in Uncooperative Environments with

Abstract. Implementing a new programming language by the means of a translator to an existing language is attractive as it provides portability over all platforms supported by the host language and reduces the development time as many low-level tasks can be delegated to the host compiler. The C and C++ programming languages are popular choices for many language implementations due to the availability of efficient compilers on many platforms, and good portability. For garbage-collected languages, however, they are not a perfect match as they provide no support for accurately discovering pointers to heap-allocated data. We evaluate the published techniques, and propose a new mechanism, lazy pointer stacks, for performing accurate garbage collection in such uncooperative environments. We implemented the new technique in the Ovm Java virtual machine with our own Java-to-C++ compiler and GCC as a back-end, and found that our technique outperforms existing approaches.