A Debugger for the Split-C Language
Steven Lumetta
(Professor D. E. Culler)
(NSF) CDA-87-22788 and NSF Graduate Fellowship

One of the major problems with the use of parallel languages by the
general community is the common lack of sufficient debugging
tools. Already unfamiliar languages are made more difficult to use
when debugging must rely on primitive methods or archaic
interfaces. To encourage more widespread use of the Split-C language,
we are developing a debugger based on the Free Software Foundation's
GDB debugger and the Tcl/Tk user interface package [1,2] developed by
John Ousterhout.  Split-C [3] is a low-level language developed at
Berkeley as part of the Castle project. The philosophy behind the
effort is close to that of C, providing a direct mapping from programs
to results and thereby allowing for careful optimization by the
programmer. It extends the standard C language with the notion of a
global address space and with a small set of parallel
operations. Through programming conventions, Split-C is able to
support shared memory, message passing, and data parallel programming
paradigms. Split-C currently runs on the CM-5 and atop PVM, but
versions for the Intel Paragon, Cray T3D, and a more efficient version
for networks of workstations are in the planning stages.

Split-C users have thus far been forced to debug with primitive tools
designed for other languages. Since these uniformly fail to recognize
some of the key concepts in Split-C (e.g., the global address space
concept), many of the people using Split-C consider them to be worse
than useless, and commonly resort to print-style debugging instead.

Our first goal is to provide a flexible graphical interface with the
standard sequential debugging capabilities for each node of the
machine or network.  The next step is to provide support for concepts
specific to Split-C, and finally to develop some of the theoretical
notions of parallel debugging that appear in the literature into
practical forms that can be used with large machines.

[1] J. K. Ousterhout, "An X11 Toolkit Based on the Tcl Language,"
Proc. USENIX Winter Conf., 1991, pp. 105-115.

[2] J. K. Ousterhout, "Tcl: An Embeddable Command Language,"
Proc. USENIX Winter Conf., 1990, pp. 133-146.

[3] D. E. Culler, A. Dusseau, S. C. Goldstein, A. Krishnamurthy,
S. Lumetta, T. von Eicken, and K. Yelick, "Parallel Programming in
Split-C," Proc. Supercomputing, 1993.