StapSDT

Runtime definition of StapSDT (Dtrace) probes within Ruby programs

This gem allows one to define StapSDT probes on Linux, and then use the StapSDT tooling to list and inspect them (mainly the bcc suite of tools)

This gem requires that libelf is installed on the system. On Ubuntu systems, do

sudo apt-get install libelf-dev

Add this line to your application's Gemfile:

gem 'stapsdt'

And then execute:

$ bundle

Or install it yourself as:

$ gem install stapsdt

An example should be worth a 1000 words. Let's create example.rb with:

require 'stapsdt'

puts "PID: #{Process.pid}"

provider = StapSDT::Provider.new('example')

probe = provider.add_probe("test", String, Integer)
provider.load

i = 0
loop do
    probe.fire("some string", i += 1)
end

and run it with bundle exec example.rb

Then, /usr/share/bcc/tools/tplist -p 25175 example:test (replace 25175 with the PID shown by the script) will display:

example:test [sema 0x0]
  1 location(s)
  2 argument(s)

Finally, sudo /usr/share/bcc/tools/trace -p 25175 -M 10 'u::test "%s - %llu" arg1, arg2'

PID     TID     COMM            FUNC             -
25175   25175   ruby            test             some string - -1241438585
25175   25175   ruby            test             some string - -1241438584
25175   25175   ruby            test             some string - -1241438583
25175   25175   ruby            test             some string - -1241438582
25175   25175   ruby            test             some string - -1241438581
25175   25175   ruby            test             some string - -1241438580
25175   25175   ruby            test             some string - -1241438579
25175   25175   ruby            test             some string - -1241438578
25175   25175   ruby            test             some string - -1241438577
25175   25175   ruby            test             some string - -1241438576

Note that the probes can be inspected and traced only after the provider has been loaded. They won't appear until then.

Thanks to Matheus Marchini who wrote this medium article showing the same capability on Node.js and Python. I would not even have realized it was possible before that.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/rock-core/ruby-stapsdt. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the Usdt project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.