Class: Dtrace::Probe

Inherits:
Object
  • Object
show all
Defined in:
lib/dtrace/probe.rb,
ext/dtrace_api.c

Overview

Using dynamically created USDT probes in Ruby programs.

Having created the following probes with Dtrace::Provider:

74777 action_controller12297 action_controller.so process_finish process-finish
74778 action_controller12297 action_controller.so process_start process-start

you can fire them with the following Ruby statements:

Dtrace::Probe::ActionController.process_start do |p|
  p.fire(request.url)
end

Note that the generated class corresponding to the provider is simply the provider class, camelized.

The generated method corresponding to the probe name (with - replaced by _) yields a probe object, on which you can call fire(), passing arguments of the appropriate types – you are responsible for any type conversions necessary.

fire() takes as many arguments as you defined for the probe: if you have generated a list of arguments to pass to fire(), use the splat operator to expand the list:

Dtrace::Probe::MyProvider.my_probe do |p|
  args_list = [ some operation to get a list ]
  p.fire(*args_list)
end

This yield/fire() syntax exposes the is-enabled feature of the generated USDT probes: if the probe is not enabled, then the yield does not happen: this allows you to put relatively expensive work in the block, and know it is only called if the probe is enabled. This way, the probe-disabled overhead of these providers is reduced to a single method call, to a C-implemented method which simply wraps the DTrace IS_ENABLED() macro for the probe.

Instance Method Summary collapse

Constructor Details

#initialize ⇒ Object

Instance Method Details

#addr ⇒ Object

#fire ⇒ Object

#is_enabled? ⇒ Boolean

Returns:

  • (Boolean)

#is_enabled_offset ⇒ Object

#probe_offset ⇒ Object