Erlang DBG and the Trace BIF

Tamas Nagy

This tutorial gives insight in the less known trace tools and mechanisms
available in Erlang. Its contents are up to date with all the latest
features in the language, including the trace BIF alongside the so ugly,
yet so useful match specifications. Its target audience consists of
programmers, testers and support engineers with a few months Erlang
experience. OTP knowledge is not a requirement. Time permitting, the
course contains hand on exercises (or demos) where users write their own
tools to test, monitor and profile the system, or adapt existing tools
to a set of predefined requirements.

Trace Bifs

Trace bifs provide a low level trace mechanism. The fact that it can be
used with out trace compiling the code makes it useful when tracing
garbage collecting, memory consumption, message passing, and other
process activities including local and global function calls. This
section looks at how to activate and deactivate the different trace
flags as well as turning them on for different processes, modules and
functions. The understanding of the trace and trace_pattern bifs are
important as they give an insight into what exactly is available for low
level debugging and are used to build many of the existing tools.  

The dbg Tool

The dbg tool is a text based debugger providing a friendly interface to
the trace bifs with small impacts on system performance. This section
introduces the tool and covers how this tool can be used in a
distributed environment or how the output can be redirected on other
nodes, log files, ports and sockets.

Match Specifications

This section covers match specifications, an Erlang term providing a low
level mechanism which will match and test the arguments passed to traced
function calls. If the match is successful, a trace message is issued
along side possible user defined events. These match specifications are
very powerful in that they allow conditional tracing on specific
function calls based on the arguments with out having to recompile or
change the code.  Due to its neglectable impact on system performance,
if used with care, match specifications can be used to detect bugs on
live systems. 

Delegates should come to the workshop with Erlang installed on their
machine.

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*Bio:* Tamas Nagy received his master's degree in Computer Science in
2007 from Eotvos Lorand University, Hungary. Both his bachelor and
master's thesis were based around Erlang and refactoring. He was
involved in the initial phases of RefactorErl, a project, a
refactoring tool for Erlang, and through an exchange program, worked
with Wrangler at the University of Kent. He is passionate about
Erlang, having been introduced to it during his university studies
more than three years ago. As a result of this passion, he has had the
opportunity to experiment his teaching techniques on computer science
students for 2 years. After joining the Erlang Training and Consulting
in early 2008, he has been involved in various commercial Erlang
related projects, ranging from configuration management to mobile
email gateways. He lives in London with his wife Aniko and cat
Rasputin.