ruby-usdt

Native DTrace probes for ruby apps

Ruby bindings for libusdt.

Applications, Libraries, and Frameworks can consume ruby-usdt to define USDT
providers at runtime for instrumentation and analysis by the DTrace framework.

Install

gem install ruby-usdt

When using Bundler to integrate ruby-usdt into a Ruby or Rails project, you will need to specify that there are git submodule dependencies:

gem "ruby-usdt", :submodules => true

Usage

# Provider.create <provider>, <module>
#
# Creates a probe
#
# returns USDT::Provider object
provider = USDT::Provider.create :ruby, :mymod

# Provider#probe *args
#
# args must be either :integer, or :string
# max 6 args (dtrace provides this many), additional args will be ignored
# returns USDT::Probe object
probe = provider.probe(:myfn, :probe, :string, :string, :integer)

# Provider#enable
# enables the probes defined with #probe
provider.enable

while true
  if probe.enabled?
    probe.fire("omg", "probe!!", 12345)
  end
  sleep 0.5
end

To see the above probe working, the following dtrace script can be used:

sudo dtrace -n 'ruby*:mymod:myfn:probe { printf("%s %s %d",
  copyinstr(arg0),
  copyinstr(arg1),
  args[2])
}'

Probes in Ruby

Introspection can be done on a probe from within Ruby using the following commands:

probe.function  => :myfn
probe.name      => :probe
probe.arguments => [:string, :string, :integer]

Interoperability

On systems with DTrace, this gem will compile C extensions that hook into USDT. On systems without DTrace, the gem should install with a noop implementation, so that probes can be added to projects without losing the ability to deploy to non-dtraceable platforms.

Additional Resources

• User-Level-Statically Defined Tracing
• DTrace Book
• Libusdt - Creating DTrace Providers at Runtime

License

The MIT License

Copyright (C) 2012 Kevin Chan

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.