psyeugenic / lttng Goto Github PK

This Erlang application, lttng, leverages the LTTng-UST JUL (Java Utility Logging) interface to enable and disable Erlang call tracing. It pushes trace-data to LTTng's ConsumerD via tracepoints implemented in NIFs.

Note: This application is a prototype and should be considered as such.

Erlang has its own logging framework, the error_logger, which would probably be a better fit for the JUL interface but in this prototype we use it to define UST tracepoints instead.

LTTng needs developer libs. You should compile and install:

• first liburcu, git clone git://git.lttng.org/userspace-rcu.git
• then LTTng-UST, git clone git://git.lttng.org/lttng-ust.git
• then LTTng-tools. git clone git://git.lttng.org/lttng-tools.git

For details, see http://lttng.org/download

To build, simply:

$ git clone [email protected]:psyeugenic/lttng.git
$ cd lttng
$ make

Make will fetch rebar via wget and then compile the source files.

Start Erlang with the lttng application in the library path and add a handler.

In Erlang:

> application:start(lttng).
ok
> lttng:add_handler(myapp, <<"user1">>, [{{erlang,display,1},true}]).
ok

The handler will specify the application and a user-defined string that is associated with a set of match specification for call tracing.

In bash shell:

$ lttng create erlang
Session erlang created.
Traces will be written in /home/egil/lttng-traces/erlang-20140513-180105

$ lttng list -j
JUL events (Logger name):
-------------------------

PID: 14424 - Name: /opt/installs/lib/erlang/erts-6.0/bin/beam.smp
      - myapp:user1 [disabled]

$ lttng enable-event -j myapp:user1
JUL event myapp:user1 created in channel channel0

$ lttng start
Tracing started for session erlang

In Erlang shell:

> erlang:display(wat).
wat
true

In bash shell:

$ lttng stop
Waiting for data availability
Tracing stopped for session erlang

$ lttng view
Trace directory: /home/egil/lttng-traces/erlang-20140513-180105

[18:02:14.810789887] (+?.?????????) palantir lttng_jul:user_erlang_trace: { cpu_id = 3 }, { pid = "<0.33.0>", type = "call", msg = "{erlang,display,[wat]}" }