mastodon/app/lib/request_pool.rb

# frozen_string_literal: true

require_relative 'connection_pool/shared_connection_pool'

class RequestPool
  def self.current
    @current ||= RequestPool.new
  end

  class Reaper
    attr_reader :pool, :frequency

    def initialize(pool, frequency)
      @pool      = pool
      @frequency = frequency
    end

    def run
      return unless frequency&.positive?

      Thread.new(frequency, pool) do |t, p|
        loop do
          sleep t
          p.flush
        end
      end
    end
  end

  MAX_IDLE_TIME = 30
  MAX_POOL_SIZE = ENV.fetch('MAX_REQUEST_POOL_SIZE', 512).to_i
  REAPER_FREQUENCY = 30
  WAIT_TIMEOUT = 5

  class Connection
    attr_reader :site, :last_used_at, :created_at, :in_use, :dead, :fresh

    def initialize(site)
      @site         = site
      @http_client  = http_client
      @last_used_at = nil
      @created_at   = current_time
      @dead         = false
      @fresh        = true
    end

    def use
      @last_used_at = current_time
      @in_use       = true

      retries = 0

      begin
        yield @http_client
      rescue HTTP::ConnectionError
        # It's possible the connection was closed, so let's
        # try re-opening it once

        close

        if @fresh || retries.positive?
          raise
        else
          @http_client = http_client
          retries     += 1
          retry
        end
      rescue
        # If this connection raises errors of any kind, it's
        # better if it gets reaped as soon as possible

        close
        @dead = true
        raise
      end
    ensure
      @fresh  = false
      @in_use = false
    end

    def seconds_idle
      current_time - (@last_used_at || @created_at)
    end

    def close
      @http_client.close
    end

    private

    def http_client
      Request.http_client.persistent(@site, timeout: MAX_IDLE_TIME)
    end

    def current_time
      Process.clock_gettime(Process::CLOCK_MONOTONIC)
    end
  end

  def initialize
    @pool   = ConnectionPool::SharedConnectionPool.new(size: MAX_POOL_SIZE, timeout: WAIT_TIMEOUT) { |site| Connection.new(site) }
    @reaper = Reaper.new(self, REAPER_FREQUENCY)
    @reaper.run
  end

  def with(site, &block)
    @pool.with(site) do |connection|
      ActiveSupport::Notifications.instrument('with.request_pool', miss: connection.fresh, host: connection.site) do
        connection.use(&block)
      end
    end
  end

  delegate :size, :flush, to: :@pool
end