Recently, there has been an effort to specify an IEEE standard for portable operating systems for open systems, called POSIX. One part of it, the POSIX 1003.4a threads extension (Pthreads for short) [12], describes the interface for light-weight threads that rely on shared memory and have a smaller context frame than processes. This paper describes and evaluates the design and implementation of a library of Pthreads calls that is solely based on UNIX. It shows that a library implementation is feasible and can result in good performance. This work can also be used as a comparison of the performance of other implementations, or as a prototyping, testing, and debugging system in the regular UNIX environment. Finally, some problems with the Pthreads standard are identified.

Concurrent real-time software is increasingly used in safety-critical embedded systems. Assuring the quality of such software requires the rigor of formal methods. In order to analyze a program formally, we must first construct a mathematical model of its behavior. In this paper, we consider the problem of constructing such models for concurrent real-time software. In particular, we provide a method for building mathematical models of real-time Ada tasking programs that are accurate enough to verify interesting timing properties, and yet abstract enough to yield a tractable analysis on nontrivial programs. Our approach differs from schedulability analysis in that we do not assume that the software has a highly restricted structure (e.g., a set of periodic tasks). Also, unlike most abstract models of real-time systems, we account for essential properties of real implementations, such as resource constraints and run-time overhead. Keywords--- timing analysis, real-time systems, program ...

The GNu Ada Runtime Library (GNARL) is being developed to support Ada 9X tasking for the Gnu NYU Ada Translator (GNAT). Together, they form a portable, freely distributable Ada 9X translation system. GNARL and GNAT communicate through a welldefined procedural interface, facilitating their independent development. Among the design goals of this translation system are portability, interoperability with other languages (in particular C), efficiency, and user extensibility. This paper provides an overview of how the GNARL supports these goals. 1 INTRODUCTION Ada requires a more complex runtime environment than most other languages; in particular, it requires support for multiple tasks. The GNu Ada Runtime Library (GNARL) is being developed at Florida State University to provide tasking support for the Gnu NYU Ada Translator (GNAT), an Ada 9X compiler and associated runtime system (RTS) being developed separately at New York University [10]. This separate development is facilitated by a we...