This paper presents Bugloo, a source level debugger for Scheme programs. It enables debugging of programs compiled into JVM bytecode by the Bigloo compiler. It aims at being easy to use because it provides a user interface. It aims at being practical to use because it is easy to deploy and because it is efficient enough to debug large programs such as the Bigloo compiler itself.

The JVM platform provides two standard APIs for implementing debuggers and profilers: JVMDI and JVMPI. One of the motivations for providing the Bigloo compiler with a JVM back-end was to benefit from these two APIs to implement a debugger for Scheme. Bugloo is this debugger. This paper presents the pros and cons of the JVM debugging infrastructure for implementing a debugger for a functional language such as Scheme. It also presents the implementation of the main features of Bugloo.

There are two main policies for scheduling thread-based concurrent programs: preemptive scheduling and cooperative scheduling. The former is known to be difficult to debug, because it is usually non-deterministic and can lead to data races or difficult thread synchronization. We believe the latter is a better model when it comes to debugging programs.

In this paper, we discuss the debugging of Scheme Fair Threads, that are based on cooperative scheduling and synchronous reactive programming. In this approach, thread communication and synchronization is achieved by means of special primitives called signals, which ease the debugging process. We present the tools we have implemented to deal with the main types of concurrent bugs that can arise in this special programming framework.