класс ActiveRecord::ConnectionAdapters::ConnectionPool

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 321
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

  # The cache of threads mapped to reserved connections, the sole purpose
  # of the cache is to speed-up +connection+ method, it is not the authoritative
  # registry of which thread owns which connection, that is tracked by
  # +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
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 372
def active_connection?
  @thread_cached_conns[connection_cache_key(Thread.current)]
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 498
def checkin(conn)
  synchronize do
    remove_connection_from_thread_cache conn

    conn._run_checkin_callbacks do
      conn.expire
    end

    @available.add conn
  end
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 489
def checkout(checkout_timeout = @checkout_timeout)
  checkout_and_verify(acquire_connection(checkout_timeout))
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 447
def clear_reloadable_connections(raise_on_acquisition_timeout = true)
  with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
    synchronize do
      @connections.each do |conn|
        if conn.in_use?
          conn.steal!
          checkin conn
        end
        conn.disconnect! if conn.requires_reloading?
      end
      @connections.delete_if(&:requires_reloading?)
      @available.clear
    end
  end
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 471
def clear_reloadable_connections!
  clear_reloadable_connections(false)
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 404
def connected?
  synchronize { @connections.any? }
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 363
def connection
  @thread_cached_conns[connection_cache_key(Thread.current)] ||= checkout
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 414
def disconnect(raise_on_acquisition_timeout = true)
  with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
    synchronize do
      @connections.each do |conn|
        if conn.in_use?
          conn.steal!
          checkin conn
        end
        conn.disconnect!
      end
      @connections = []
      @available.clear
    end
  end
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 436
def disconnect!
  disconnect(false)
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 544
def reap
  stale_connections = synchronize do
    @connections.select do |conn|
      conn.in_use? && !conn.owner.alive?
    end.each do |conn|
      conn.steal!
    end
  end

  stale_connections.each do |conn|
    if conn.active?
      conn.reset!
      checkin conn
    else
      remove conn
    end
  end
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 383
def release_connection(owner_thread = Thread.current)
  if conn = @thread_cached_conns.delete(connection_cache_key(owner_thread))
    checkin conn
  end
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 512
def remove(conn)
  needs_new_connection = false

  synchronize do
    remove_connection_from_thread_cache conn

    @connections.delete conn
    @available.delete conn

    # @available.any_waiting? => true means that prior to removing this
    # conn, the pool was at its max size (@connections.size == @size)
    # this would mean that any threads stuck waiting in the queue wouldn't
    # know they could checkout_new_connection, so let's do it for them.
    # Because condition-wait loop is encapsulated in the Queue class
    # (that in turn is oblivious to ConnectionPool implementation), threads
    # that are "stuck" there are helpless, they have no way of creating
    # new connections and are completely reliant on us feeding available
    # connections into the Queue.
    needs_new_connection = @available.any_waiting?
  end

  # This is intentionally done outside of the synchronized section as we
  # would like not to hold the main mutex while checking out new connections,
  # thus there is some chance that needs_new_connection information is now
  # stale, we can live with that (bulk_make_new_connections will make
  # sure not to exceed the pool's @size limit).
  bulk_make_new_connections(1) if needs_new_connection
end

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 393
def with_connection
  unless conn = @thread_cached_conns[connection_cache_key(Thread.current)]
    conn = connection
    fresh_connection = true
  end
  yield conn
ensure
  release_connection if fresh_connection
end