Implementing a new low-level tasking support for the GNAT runtime system

Abstract

This paper describes the main design goals and implementation choices of JTK, a library which provides simple tasking support, loosely based on POSIX threads. It has been designed to provide the lowlevel tasking support for GNAT, it is completely written in Ada, and it is usable on top of a traditional operating system (providing user-level threads) as well as layered over a bare machine. Its main design motivation is the desire to experiment with a low-level tasking implementation that fits well with GNAT tasking requirements. Currently, JTK provides a priority driven threading model, with preemptive scheduling, facilities for signal handling, and primitives to provide mutual exclusion and synchronized waiting. The long-term target of JTK is to provide all the facilities that GNAT needs to satisfy full Annex D semantics.