Tracing Ruby Applications Execution in 4 Lines
I was researching a simple way to trace ruby code, so the problem I tried to solve (as usual) is to understand the code infront of me even more, so I need some monitor, when I open a rails server and I navigate around, I need to see the methods executed and where is it located, I need to see that in realtime.
Turns out the solution is very simple, as Ruby has TracePoint module, you can
use it to log any thing gets called in your application, so adding this snippet
to your rails initializers or anywhere before your application starts.
TracePoint.new(:call) do |tp|
puts "#{ tp.path }:#{tp.lineno}\t#{ tp.defined_class }\t#{ tp.method_id }"
end.enable
That should print every method call to your standard output, but you’ll discover
early that everything is too much, you need to ignore method calls that doesn’t
belong to your application code, like puma server method calls, or any
external gem calls, so lets limit it to our application by adding a suffix if
to the puts line.
TracePoint.new(:call) do |tp|
puts "#{ tp.path }:#{tp.lineno}\t#{ tp.defined_class }\t#{ tp.method_id }" if tp.path.include?('/app/')
end.enable
that should limit it to method calls located under /app directory, but as you
know your application also logs stuff, so it doesn’t make sense to log to
STDOUT, lets separate that logs to a log file, and as my /tmp directory is a
tmpfs mapped to memory not SSD, it’ll be fast and volatile, so I don’t care to
clean it up afterwards.
And for that I’ll createa a logger to a file in /tmp and use it to print these
executions
logger = Logger.new('/tmp/trace.log', File::WRONLY | File::APPEND | File::CREAT)
TracePoint.new(:call) do |tp|
logger.debug "#{ tp.path }:#{tp.lineno}\t#{ tp.defined_class }\t#{ tp.method_id }" if tp.path.include?('/app/')
end.enable
So now you can tail -f /tmp/trace.log to see your application execution in
realtime, but you’ll learn also that you need to filter the logs or search in
them, so that can be done by piping your log file to fzf you can find it
here so to see your logs and search through
them now you can execute this in your shell
cat /tmp/trace.log | fzf
If you want to have your whole screen filled with fzf and the input prompt to
the top you can add --layout=reverse
cat /tmp/trace.log | fzf --layout=reverse
