Class: OneApm::Agent::Threading::BacktraceService

Inherits:
Object
  • Object
show all
Defined in:
lib/one_apm/support/backtrace/backtrace_service.rb

Constant Summary collapse

OA_ALL_TRANSACTIONS = 
"**ALL**".freeze
OA_MAX_BUFFER_LENGTH = 
500

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(event_listener = nil) ⇒ BacktraceService

Returns a new instance of BacktraceService.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 18

def initialize(event_listener=nil)
  @profiles = {}
  @buffer = {}

  # synchronizes access to @profiles and @buffer above
  @lock = Mutex.new

  @running = false
  @profile_agent_code = false
  @worker_loop = OneApm::Support::WorkerLoop.new

  # Memoize overhead % to avoid getting stale OR looked up every poll
  @overhead_percent_threshold = OneApm::Manager.config[:'xray_session.max_profile_overhead']
  OneApm::Manager.config.register_callback(:'xray_session.max_profile_overhead') do |new_value|
    @overhead_percent_threshold = new_value
  end

  if event_listener
    event_listener.subscribe(:transaction_finished, &method(:on_transaction_finished))
  end
end

Instance Attribute Details

#buffer ⇒ Object (readonly)

Returns the value of attribute buffer.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 13

def buffer
  @buffer
end

#effective_polling_period ⇒ Object

Returns the value of attribute effective_polling_period.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 13

def effective_polling_period
  @effective_polling_period
end

#overhead_percent_threshold ⇒ Object (readonly)

Returns the value of attribute overhead_percent_threshold.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 13

def overhead_percent_threshold
  @overhead_percent_threshold
end

#profile_agent_code ⇒ Object

Returns the value of attribute profile_agent_code.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 16

def profile_agent_code
  @profile_agent_code
end

#profiles ⇒ Object (readonly)

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 167

def profiles
  @profiles
end

#worker_loop ⇒ Object (readonly)

Returns the value of attribute worker_loop.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 13

def worker_loop
  @worker_loop
end

#worker_thread ⇒ Object

Returns the value of attribute worker_thread.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 16

def worker_thread
  @worker_thread
end

Class Method Details

.is_supported? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 9

def self.is_supported?
  RUBY_VERSION >= "1.9.2"
end

Instance Method Details

#adjust_polling_time(now, poll_start) ⇒ Object

If our overhead % exceeds the threshold, bump the next poll period relative to how much larger our overhead is than allowed



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 227

def adjust_polling_time(now, poll_start)
  duration = now - poll_start
  overhead_percent = duration / effective_polling_period

  if overhead_percent > self.overhead_percent_threshold
    scale_up_by = overhead_percent / self.overhead_percent_threshold
    worker_loop.period = effective_polling_period * scale_up_by
  else
    worker_loop.period = effective_polling_period
  end
end

#aggregate_backtraces(backtraces, name, start, duration, thread) ⇒ Object

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 117

def aggregate_backtraces(backtraces, name, start, duration, thread)
  end_time = start + duration
  backtraces.each do |(timestamp, backtrace)|
    if timestamp >= start && timestamp < end_time
      @profiles[name].aggregate(backtrace, :request, thread)
    end
  end
end

#aggregate_global_backtrace(backtrace, bucket, thread) ⇒ Object

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 197

def aggregate_global_backtrace(backtrace, bucket, thread)
  if @profiles[OA_ALL_TRANSACTIONS]
    @profiles[OA_ALL_TRANSACTIONS].aggregate(backtrace, bucket, thread)
  end
end

#buffer_backtrace_for_thread(thread, timestamp, backtrace, bucket) ⇒ Object

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 185

def buffer_backtrace_for_thread(thread, timestamp, backtrace, bucket)
  if should_buffer?(bucket)
    @buffer[thread] ||= []
    if @buffer[thread].length < OA_MAX_BUFFER_LENGTH
      @buffer[thread] << [timestamp, backtrace]
    else
      OneApm::Manager.increment_metric('Supportability/XraySessions/DroppedBacktraces')
    end
  end
end

#find_effective_polling_period ⇒ Object

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 216

def find_effective_polling_period
  @profiles.values.map { |p| p.requested_period }.min
end

#harvest(transaction_name) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 90

def harvest(transaction_name)
  @lock.synchronize do
    if @profiles[transaction_name]
      profile = @profiles.delete(transaction_name)
      profile.finished_at = Time.now
      @profiles[transaction_name] = ThreadProfile.new(profile.command_arguments)
      profile
    end
  end
end

#need_backtrace?(bucket) ⇒ Boolean

This method is expected to be called with @lock held.

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 175

def need_backtrace?(bucket)
  (
    bucket != :ignore &&
    (@profiles[OA_ALL_TRANSACTIONS] || should_buffer?(bucket))
  )
end

#on_transaction_finished(payload) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 101

def on_transaction_finished(payload)
  name     = payload[:name]
  start    = payload[:start_timestamp]
  duration = payload[:duration]
  thread   = payload[:thread] || Thread.current
  @lock.synchronize do
    backtraces = @buffer.delete(thread)
    if backtraces && @profiles.has_key?(name)
      aggregate_backtraces(backtraces, name, start, duration, thread)
    end
  end
end

#poll ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 150

def poll
  poll_start = Time.now

  @lock.synchronize do
    AgentThread.list.each do |thread|
      sample_thread(thread)
    end
    @profiles.each_value { |p| p.increment_poll_count }
    @buffer.delete_if { |thread, _| !thread.alive? }
  end

  end_time = Time.now
  adjust_polling_time(end_time, poll_start)
  record_supportability_metrics(end_time, poll_start)
end

#record_polling_time(now, poll_start) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 244

def record_polling_time(now, poll_start)
  OneApm::Manager.record_metric('Supportability/ThreadProfiler/PollingTime', now - poll_start)
end

#record_skew(poll_start) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 248

def record_skew(poll_start)
  if @last_poll
    skew = poll_start - @last_poll - worker_loop.period
    OneApm::Manager.record_metric('Supportability/ThreadProfiler/Skew', skew)
  end
  @last_poll = poll_start
end

#record_supportability_metrics(now, poll_start) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 239

def record_supportability_metrics(now, poll_start)
  record_polling_time(now, poll_start)
  record_skew(poll_start)
end

#running? ⇒ Boolean

Public interface

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 42

def running?
  @running
end

#sample_thread(thread) ⇒ Object

This method is expected to be called with @lock held.



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 204

def sample_thread(thread)
  bucket = AgentThread.bucket_thread(thread, @profile_agent_code)

  if need_backtrace?(bucket)
    timestamp = Time.now.to_f
    backtrace = AgentThread.scrub_backtrace(thread, @profile_agent_code)
    aggregate_global_backtrace(backtrace, bucket, thread)
    buffer_backtrace_for_thread(thread, timestamp, backtrace, bucket)
  end
end

#should_buffer?(bucket) ⇒ Boolean

This method is expected to be called with @lock held.

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 170

def should_buffer?(bucket)
  bucket == :request && @profiles.keys.any? { |k| k != OA_ALL_TRANSACTIONS }
end

#should_profile_agent_code? ⇒ Boolean

This method is expected to be called with @lock held.

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 221

def should_profile_agent_code?
  @profiles.values.any? { |p| p.profile_agent_code }
end

#start ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 126

def start
  return if @running || !self.class.is_supported?

  @running = true
  self.worker_thread = AgentThread.create('Backtrace Service') do
    # Not passing period because we expect it's already been set.
    self.worker_loop.run(&method(:poll))
  end
end

#stop ⇒ Object

This method is expected to be called with @lock held



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 137

def stop
  return unless @running
  @running = false
  self.worker_loop.stop

  @buffer = {}
end

#subscribe(transaction_name, command_arguments = {}) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 46

def subscribe(transaction_name, command_arguments={})
  if !self.class.is_supported?
    OneApm::Manager.logger.debug("Backtracing not supported, so not subscribing transaction '#{transaction_name}'")
    return
  end

  OneApm::Manager.logger.debug("Backtrace Service subscribing transaction '#{transaction_name}'")

  profile = ThreadProfile.new(command_arguments)

  @lock.synchronize do
    @profiles[transaction_name] = profile
    update_values_from_profiles
  end

  start
  profile
end

#subscribed?(transaction_name) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 84

def subscribed?(transaction_name)
  @lock.synchronize do
    @profiles.has_key?(transaction_name)
  end
end

#unsubscribe(transaction_name) ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 65

def unsubscribe(transaction_name)
  return unless self.class.is_supported?

  OneApm::Manager.logger.debug("Backtrace Service unsubscribing transaction '#{transaction_name}'")
  @lock.synchronize do
    @profiles.delete(transaction_name)
    if @profiles.empty?
      stop
    else
      update_values_from_profiles
    end
  end
end

#update_values_from_profiles ⇒ Object 



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# File 'lib/one_apm/support/backtrace/backtrace_service.rb', line 79

def update_values_from_profiles
  self.effective_polling_period = find_effective_polling_period
  self.profile_agent_code = should_profile_agent_code?
end