[Pl-seminar] Semantics Seminar Schedule

Mitchell Wand wand at ccs.neu.edu
Mon Jan 22 16:03:28 EST 2007

NU Programming Languages Seminar
Wednesday, 1/24/07
Room 366 WVH (http://www.ccs.neu.edu/home/wand/directions.html)

Debugging Backwards in Time
Bil Lewis

What if a debugger could allow you to simply step BACKWARDS?
Instead of all that hassle with guessing where to put
breakpoints and the fear of typing "continue" one too many
times... What if you could simply go backwards to see what
went wrong?

This is the essence of the "Omniscient Debugger" -- it remembers
everything that happened during the run of a program, and allows
the programmer to "step backwards in time" to see what happened
at any point of the program. All variable values, all objects,
all method calls, all exceptions are recorded and the programmer
can now look at anything that happened at any time.

In this talk, I will describe the design of the "ODB" -- an
implementation of Omniscient Debugging for Java programs -- and
discuss the various costs and trade-offs. The last half of the
talk will be a demonstration of the ODB, showing how the various
pieces of data are displayed and how the programmer can
"navigate" through time to see what the program was doing, where
values were set, when various threads ran, etc.

At the conclusion of the talk, the audience will be invited
to use the ODB to find some actual bugs. Anyone having a
laptop with Java on it can download the ODB (beforehand!)
and try using it to find the bugs themselves.


The ODB is an experimental program under development. It is
written in 100% pure Java and has been tested under Solaris,
MacOS, and Windows. It is freely available at my web site:


Bil Lewis is a computer scientist currently teaching at Tufts
University. He has worked on natural
language understanding, expert systems, language design, and
programming tools.  He studied at Ripon College, the University
of Indiana, and Penn. He has taught at Stanford and for numerous
companies. He has worked at Stanford Research Institute, the FMC
AI Center, and Sun Microsystems.  He wrote "GNU Emacs Lisp", the
"Threads Primer", "Multithreaded Programming with PThreads", and
"Multithreaded Programming with Java".

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