Thread-local SCP Tracing Plugin

[ffloyd]

Problem

When you're debugging a business logic based on SharedContextPipeline it's nice to have an optional ability to temporarily turn on logging of a steps' execution. But writing it just to a text log is not convenient for debugging - because the text is not data.

Proposal

Let's use thread local variables to store execution history. The code below is merely a basic example and final behavior might be different.

class ApplicationOperation < Flows::SharedContextPipeline
  if Rails.env.development? || Rails.env.test?
    include Flows::Plugin::Tracing
   
    tracing true
  end
end

class MyOperation << ApplicationOperation
  # some steps here
  # some another operation can be executed inside steps
end

# use via wrap
trace = Flows::Plugin::Tracing.wrap do
  MyOperation.call(a: 1, b: 2)
end

# use via toggles
Flows::Plugin::Tracing.start
MyOperation.call(a: 1, b: 2)
trace = Flow::Plugin::Tracing.finish


puts trace.to_s
# Will print all the steps executions for all the operations
# inherited from ApplicationOperation. The order is the execution order.
# Output contains operation class name, step name, context string representation
# at the moment of step execution, a string representation of
# returned Result Object and WALL execution time.

trace.to_a
# returns the same data in the form of an array of 1-level deep hashes.

trace.benchmark.to_s
trace.benchmark.to_a
# contains statistic about slowest operations and steps,
# also counts executions and calculates average execution WALL time

trace.benchmark.to_plantuml
# it's also possible to draw UML Activity diagrams in PlantUML format.
# It includes benchmark info and visualizes execution-time relations between operations.

Implementation hints and requirements

Ruby is mutable. If you just save some hash into tracing data - it can be changed during the rest of execution. #dup, #clone and #freeze have no guarantees about nested data.

Therefore, the most reliable way is to serialize data to String using #inspect and store this string inside tracing data objects.

#6 must be done before this work.