João Lourenço

In the recent past, multiple techniques and tools have been proposed and contributed to improve the distributed debugging functionalities, in several distinct aspects, such as handling the non-determinism, allowing cyclic interactive debugging of parallel programs, and providing more user-friendly interfaces. However, most of these tools are tied to a specific programming language and provide rigid graphical user interfaces. So they cannot easily adapt to support distinct abstraction levels or user interfaces. They also don't provide adequate support for cooperation with other tools in a software engineering environment. In this paper we discuss several dimensions which may contribute to develop more flexible distributed debuggers. We describe Fiddle, a distributed debugging tool which aims at overcoming some of the above limitations.

Software Transactional Memory algorithms associate metadata with the memory locations accessed during a transactions lifetime. This metadata may be stored in an external table and accessed by way of a function that maps the address of each memory location with the table entry that keeps its metadata (this is the out-place or external scheme); or alternatively may be stored adjacent to the associated memory cell by wrapping them together (the in-place scheme). In transactional memory multi-version algorithms, several versions of the same memory location may exist. The efficient implementation of these algorithms requires a one-to-one correspondence between each memory location and its list of past versions, which is stored as metadata. In this chapter we address the matter of the efficient implementation of multi-version algorithms in Java by proposing and evaluating a novel in-place metadata scheme for the Deuce framework. This new scheme is based in Java Bytecode transformation techniques and its use requires no changes to the application code. Experimentation indicates that multi-versioning STM algorithms implemented using our new in-place scheme are in average 6 × faster than when implemented with the out-place scheme.

We discuss debugging prototypes that can easily support new functionalities, depending on the requirements of high-level computational models, and allowing a coherent integration with other tools in a software engineering environment. Concerning the first aspect, we propose a framework that identifies two distinct levels of functionalities that should be supported by a parallel and distributed debugger using: a process and thread-level, and a coordination level concerning sets of processes or threads. An incremental approach is used to effectively develop prototypes that support both functionalities. Concerning the second aspect, we discuss how the interfacing with other tools has influenced the design of a process-level debugging interface (PDBG) and a distributed monitoring and control layer called (DAMS).