class method self.new

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 120
      def initialize(pool_config)
        super()

        @pool_config = pool_config
        @db_config = pool_config.db_config
        @role = pool_config.role
        @shard = pool_config.shard

        @checkout_timeout = db_config.checkout_timeout
        @idle_timeout = db_config.idle_timeout
        @size = db_config.pool

        # This variable tracks the cache of threads mapped to reserved connections, with the
        # sole purpose of speeding up the +connection+ method. It is not the authoritative
        # registry of which thread owns which connection. Connection ownership is tracked by
        # the +connection.owner+ attr on each +connection+ instance.
        # The invariant works like this: if there is mapping of <tt>thread => conn</tt>,
        # then that +thread+ does indeed own that +conn+. However, an absence of such
        # mapping does not mean that the +thread+ doesn't own the said connection. In
        # that case +conn.owner+ attr should be consulted.
        # Access and modification of <tt>@thread_cached_conns</tt> does not require
        # synchronization.
        @thread_cached_conns = Concurrent::Map.new(initial_capacity: @size)

        @connections         = []
        @automatic_reconnect = true

        # Connection pool allows for concurrent (outside the main +synchronize+ section)
        # establishment of new connections. This variable tracks the number of threads
        # currently in the process of independently establishing connections to the DB.
        @now_connecting = 0

        @threads_blocking_new_connections = 0

        @available = ConnectionLeasingQueue.new self

        @lock_thread = false

        @async_executor = build_async_executor

        @reaper = Reaper.new(self, db_config.reaping_frequency)
        @reaper.run
      end