class method self.new

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 323
      def initialize(spec)
        super()

        @spec = spec

        @checkout_timeout = (spec.config[:checkout_timeout] && spec.config[:checkout_timeout].to_f) || 5
        @reaper = Reaper.new(self, (spec.config[:reaping_frequency] && spec.config[:reaping_frequency].to_f))
        @reaper.run

        # default max pool size to 5
        @size = (spec.config[:pool] && spec.config[:pool].to_i) || 5

        # 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 a 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 +@thread_cached_conns+ 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
      end