Thread Libraries in C
Java Threads
Threads in Functional Languages
Reactive Approach
Chores and Filaments

1. Introduction
2. Rationale
3. API Overview
4. API
5. Examples
6. Related Work
7. Conclusion
8. Man Pages

Several thread libraries exist for C. Among them, the Pthreads library [17] implements the POSIX standard for preemptive threads. LinuxThreads [4] is an implementation of Pthreads for Linux; it is based on kernel-level threads. Quick Threads [14] provides programmers with a minimal support for multithreading at user-space level. Basically, it implements context-switching in assembly code, and is thus a low-level solution to multithreading. Gnu Portable Threads [11] (GNU Pth) is a library of purely cooperative threads which has portability as main objective. The Next Generation POSIX Threading project [5] proposes to extend GNU Pth to the M:N model, with Linux SMP machines as target.

Java introduce threads at language level. Actually, threads are generally heavily used in Java, for example when graphics or networking is involved. No assumption is made on the way threads are scheduled (cooperative or preemptive scheduling) wich makes Java multithreaded systems difficult to program and to port [13]. This difficulty is pointed out by the suppression from the recent versions of the language of the threads primitives to gain fine control over threads [3]. A first version of FairThreads has been proposed in the context of the Java language [7] in order to simplify concurrent programming in Java.

Threads are used in several ML-based languages such as CML [18]. CML is preemptively scheduled and threads communication is synchronous and based on channels. Threads are also introduced in CAML [2]; they are implemented by time-sharing on a single processor, and thus cannot benefit from multiprocessors machines. FairThreads has been recently introduced in the Bigloo [1] implementation of Scheme. The present version only supports linked threads, and special constructs are introduced to deal with non-blocking I/Os.

FairThreads actually comes out from the so-called reactive approach [6]. In this approach, one basically has instants and broadcast events. As opposite to synchronous languages [12] such as Esterel, the absence of an event during one instant cannot be decided before the end of this very instant. As a consequence, the reaction to the absence of one event is delayed to the next instant. This is a way to solve so-called "causality problems" which are raised with synchronous languages, and which are obstacles to modularity. The Reactive-C [8] language was the first proposal for reactive programming in C; in this respect, FairThreads can be considered as a descendant of it.

Chores [10] and filaments [15] are small pieces of code that do not have private stack and are never preempted. Chores and filaments are designed for fine-grain parallelism programming on shared-memory machines. Chores and filaments are completely executed and cannot be suspended nor resumed. Generally, a pool of threads is devoted to execute them. Chores and chunk-based techniques are described in details in the context of the Java language in [9] and [13]. Automata in FairThreads are close to chores and filaments, but give programmers more freedom for direct coding of states-based algorithms. Automata are also related to mode automata [16] in which states capture the notion of a running mode in the context of the synchronous language Lustre.