appsignal/appsignal

# frozen_string_literal: true

module Appsignal
  # {Appsignal::GarbageCollectionProfiler} wraps Ruby's `GC::Profiler` to be
  # able to track garbage collection time for multiple transactions, while
  # constantly clearing `GC::Profiler`'s total_time to make sure it doesn't
  # leak memory by keeping garbage collection run samples in memory.
  #
  # @api private
  class GarbageCollectionProfiler
    def self.lock
      @lock ||= Mutex.new
    end

    def initialize
      @total_time = 0
    end

    # Whenever {#total_time} is called, the current `GC::Profiler#total_time`
    # gets added to `@total_time`, after which `GC::Profiler.clear` is called
    # to prevent it from leaking memory. A class-level lock is used to make
    # sure garbage collection time is never counted more than once.
    #
    # Whenever `@total_time` gets above two billion milliseconds (about 23
    # days), it's reset to make sure the result fits in a signed 32-bit
    # integer.
    #
    # @return [Integer]
    def total_time
      lock.synchronize do
        @total_time += (internal_profiler.total_time * 1000).round
        internal_profiler.clear
      end

      @total_time = 0 if @total_time > 2_000_000_000

      @total_time
    end

    private

    def internal_profiler
      GC::Profiler
    end

    def lock
      self.class.lock
    end
  end

  # {Appsignal::NilGarbageCollectionProfiler} is a dummy profiler
  # that always returns 0 as the total time.
  # Used when we don't want any profile information
  #
  # @api private
  class NilGarbageCollectionProfiler
    def total_time
      0
    end
  end
end