Forcing JRuby garbage collection for Sidekiq

sidekiq_garbage_collector.rb

require 'java'

module App
  module Middleware
    # Middleware for forcing run of the garbage collector after a task
    # finishes. A "server," in this case, is any code that is overseeing
    # the processing of an asynchronous queue.
    class SidekiqGarbageCollector
      # Garbage collection will only be forced if the amount of
      # memory used exceeds this constant (represented as bytes in
      # base 2). See #memory_threshold_met? for more info on how this
      # constant is applied
      MEMORY_THRESHOLD = 1024 * 1024 * 512 # => 512 MB (base-2)

      # @return [java.lang.Runtime] A reference to the environment
      #   runtime object
      attr_reader :runtime

      # Creates a new SidekiqGarbageCollector instance
      #
      # @param [Hash] options A hash of options to configure the
      #   SidekiqServerLogger instance. Should be `nil`
      def initialize(options=nil)
        @runtime = java.lang.Runtime.get_runtime
      end

      # Called by Sidekiq when a job is being processed
      #
      # @param [#perform] worker An instance of the worker class
      #   which will actually process this job
      # @param [Hash] msg Hash of arguments which will be passed to
      #   #perform on the worker instance
      # @queue [String] queue Name of the queue that the job is coming
      #   from
      def call(worker, msg, queue)
        yield
        java.lang.System.gc() if memory_threshold_met?
      end

      private

      # Determines whether the allocated memory is above given threshold.
      # This is determined as the memory for the environment runtime,
      # not just the thread this worker is running in, by subtracting
      # the amount of remaining free memory reserved for the heap from
      # the total memory reserved for the heap.
      #
      # @return [TrueClass, FalseClass] whether the memory threshold has
      #   been met
      def memory_threshold_met?
        MEMORY_THRESHOLD < runtime.total_memory - runtime.free_memory
      end

    end
  end
end

workers.rb

require 'middleware/sidekiq_garbage_collector'

Sidekiq.configure_server do |config|
  config.server_middleware do |chain|
    chain.add App::Middleware::SidekiqGarbageCollector
  end
end