Design and Implementation of TinyGALS: A Programming Model for ...

1 Introduction
Emerging embedded systems, such as sensor networks [41], intelligent vehicle/highway
systems [23], smart office spaces [38, 37], peer-to-peer collaborative cell phones and PDAs
[14], are usually networked and event-driven. In these systems, the communication network
is typically formed in an ad hoc manner, and the embedded computers must react to many
(typically unstructured) stimuli, including physical events, user commands, and messages
from other systems. In other words, external events drive the computation in the embedded
system.
As the complexity of networked embedded systems grows, the costs of developing
software for these systems increases dramatically. Embedded software designers face is-
sues such as maintaining consistent state across multiple tasks, handling interrupts, avoid-
ing deadlock, scheduling concurrent threads, managing resources, and conserving power
[17, 26]. Typical technologies for developing embedded software, inherited from writing
device drivers and optimizing assembly code to achieve a fast response and a small memory
footprint, do not scale with the application complexity. In fact, it was not until recently that
“high-level” languages such as C and C++ replaced assembly language as the dominant
embedded software programming languages. Most of these high-level languages, however,
are designed for writing sequential programs to run on an operating system and fail to
handle concurrency intrinsically.
Modern software engineering practices advocate the use of software components such
as standard libraries, objects, and software services to reduce redundant code develop-
ment and improve productivity. However, when developing a component it is not foresee-
able whether it should lock any resources. A software component that does not include
synchronization code may not be thread-safe, and may exhibit unexpected behavior when
composed with other components. On the other hand, if a software component is developed
with resource synchronization in mind, then it may be overspecified in an application that
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