class OneApm::Agent::Threading::BacktraceService

Constants

OA_ALL_TRANSACTIONS
OA_MAX_BUFFER_LENGTH

Attributes

buffer[R]
effective_polling_period[R]
overhead_percent_threshold[R]
profile_agent_code[RW]
profiles[R]

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

worker_loop[R]
worker_thread[RW]

Public Class Methods

is_supported?() click to toggle source
# File lib/one_apm/support/backtrace/backtrace_service.rb, line 9
def self.is_supported?
  RUBY_VERSION >= "1.9.2"
end
new(event_listener=nil) click to toggle source
# 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

Public Instance Methods

adjust_polling_time(now, poll_start) click to toggle source

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

# 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) click to toggle source

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

# 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) click to toggle source

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

# 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) click to toggle source

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

# 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
effective_polling_period=(new_period) click to toggle source
# File lib/one_apm/support/backtrace/backtrace_service.rb, line 145
def effective_polling_period=(new_period)
  @effective_polling_period = new_period
  self.worker_loop.period = new_period
end
find_effective_polling_period() click to toggle source

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

# 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) click to toggle source
# 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) click to toggle source

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

# 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) click to toggle source
# 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() click to toggle source
# 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) click to toggle source
# 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) click to toggle source
# 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) click to toggle source
# 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?() click to toggle source

Public interface

# File lib/one_apm/support/backtrace/backtrace_service.rb, line 42
def running?
  @running
end
sample_thread(thread) click to toggle source

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

# 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) click to toggle source

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

# 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?() click to toggle source

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

# 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() click to toggle source
# 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() click to toggle source

This method is expected to be called with @lock held

# 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={}) click to toggle source
# 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) click to toggle source
# 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) click to toggle source
# 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() click to toggle source
# 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