Skip to content
This repository
tag: v3.0.11
file 364 lines (323 sloc) 13.228 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364
require 'thread'
require 'monitor'
require 'set'
require 'active_support/core_ext/module/synchronization'

module ActiveRecord
  # Raised when a connection could not be obtained within the connection
  # acquisition timeout period.
  class ConnectionTimeoutError < ConnectionNotEstablished
  end

  module ConnectionAdapters
    # Connection pool base class for managing Active Record database
    # connections.
    #
    # == Introduction
    #
    # A connection pool synchronizes thread access to a limited number of
    # database connections. The basic idea is that each thread checks out a
    # database connection from the pool, uses that connection, and checks the
    # connection back in. ConnectionPool is completely thread-safe, and will
    # ensure that a connection cannot be used by two threads at the same time,
    # as long as ConnectionPool's contract is correctly followed. It will also
    # handle cases in which there are more threads than connections: if all
    # connections have been checked out, and a thread tries to checkout a
    # connection anyway, then ConnectionPool will wait until some other thread
    # has checked in a connection.
    #
    # == Obtaining (checking out) a connection
    #
    # Connections can be obtained and used from a connection pool in several
    # ways:
    #
    # 1. Simply use ActiveRecord::Base.connection as with Active Record 2.1 and
    # earlier (pre-connection-pooling). Eventually, when you're done with
    # the connection(s) and wish it to be returned to the pool, you call
    # ActiveRecord::Base.clear_active_connections!. This will be the
    # default behavior for Active Record when used in conjunction with
    # Action Pack's request handling cycle.
    # 2. Manually check out a connection from the pool with
    # ActiveRecord::Base.connection_pool.checkout. You are responsible for
    # returning this connection to the pool when finished by calling
    # ActiveRecord::Base.connection_pool.checkin(connection).
    # 3. Use ActiveRecord::Base.connection_pool.with_connection(&block), which
    # obtains a connection, yields it as the sole argument to the block,
    # and returns it to the pool after the block completes.
    #
    # Connections in the pool are actually AbstractAdapter objects (or objects
    # compatible with AbstractAdapter's interface).
    #
    # == Options
    #
    # There are two connection-pooling-related options that you can add to
    # your database connection configuration:
    #
    # * +pool+: number indicating size of connection pool (default 5)
    # * +wait_timeout+: number of seconds to block and wait for a connection
    # before giving up and raising a timeout error (default 5 seconds).
    class ConnectionPool
      attr_reader :spec, :connections

      # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification
      # object which describes database connection information (e.g. adapter,
      # host name, username, password, etc), as well as the maximum size for
      # this ConnectionPool.
      #
      # The default ConnectionPool maximum size is 5.
      def initialize(spec)
        @spec = spec

        # The cache of reserved connections mapped to threads
        @reserved_connections = {}

        # The mutex used to synchronize pool access
        @connection_mutex = Monitor.new
        @queue = @connection_mutex.new_cond

        # default 5 second timeout unless on ruby 1.9
        @timeout = spec.config[:wait_timeout] || 5

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

        @connections = []
        @checked_out = []
      end

      # Retrieve the connection associated with the current thread, or call
      # #checkout to obtain one if necessary.
      #
      # #connection can be called any number of times; the connection is
      # held in a hash keyed by the thread id.
      def connection
        @reserved_connections[current_connection_id] ||= checkout
      end

      # Signal that the thread is finished with the current connection.
      # #release_connection releases the connection-thread association
      # and returns the connection to the pool.
      def release_connection(with_id = current_connection_id)
        conn = @reserved_connections.delete(with_id)
        checkin conn if conn
      end

      # If a connection already exists yield it to the block. If no connection
      # exists checkout a connection, yield it to the block, and checkin the
      # connection when finished.
      def with_connection
        connection_id = current_connection_id
        fresh_connection = true unless @reserved_connections[connection_id]
        yield connection
      ensure
        release_connection(connection_id) if fresh_connection
      end

      # Returns true if a connection has already been opened.
      def connected?
        !@connections.empty?
      end

      # Disconnects all connections in the pool, and clears the pool.
      def disconnect!
        @reserved_connections.each do |name,conn|
          checkin conn
        end
        @reserved_connections = {}
        @connections.each do |conn|
          conn.disconnect!
        end
        @connections = []
      end

      # Clears the cache which maps classes
      def clear_reloadable_connections!
        @reserved_connections.each do |name, conn|
          checkin conn
        end
        @reserved_connections = {}
        @connections.each do |conn|
          conn.disconnect! if conn.requires_reloading?
        end
        @connections.delete_if do |conn|
          conn.requires_reloading?
        end
      end

      # Verify active connections and remove and disconnect connections
      # associated with stale threads.
      def verify_active_connections! #:nodoc:
        clear_stale_cached_connections!
        @connections.each do |connection|
          connection.verify!
        end
      end

      # Return any checked-out connections back to the pool by threads that
      # are no longer alive.
      def clear_stale_cached_connections!
        keys = @reserved_connections.keys - Thread.list.find_all { |t|
          t.alive?
        }.map { |thread| thread.object_id }
        keys.each do |key|
          checkin @reserved_connections[key]
          @reserved_connections.delete(key)
        end
      end

      # Check-out a database connection from the pool, indicating that you want
      # to use it. You should call #checkin when you no longer need this.
      #
      # This is done by either returning an existing connection, or by creating
      # a new connection. If the maximum number of connections for this pool has
      # already been reached, but the pool is empty (i.e. they're all being used),
      # then this method will wait until a thread has checked in a connection.
      # The wait time is bounded however: if no connection can be checked out
      # within the timeout specified for this pool, then a ConnectionTimeoutError
      # exception will be raised.
      #
      # Returns: an AbstractAdapter object.
      #
      # Raises:
      # - ConnectionTimeoutError: no connection can be obtained from the pool
      # within the timeout period.
      def checkout
        # Checkout an available connection
        @connection_mutex.synchronize do
          loop do
            conn = if @checked_out.size < @connections.size
                     checkout_existing_connection
                   elsif @connections.size < @size
                     checkout_new_connection
                   end
            return conn if conn

            @queue.wait(@timeout)

            if(@checked_out.size < @connections.size)
              next
            else
              clear_stale_cached_connections!
              if @size == @checked_out.size
                raise ConnectionTimeoutError, "could not obtain a database connection#{" within #{@timeout} seconds" if @timeout}. The max pool size is currently #{@size}; consider increasing it."
              end
            end

          end
        end
      end

      # Check-in a database connection back into the pool, indicating that you
      # no longer need this connection.
      #
      # +conn+: an AbstractAdapter object, which was obtained by earlier by
      # calling +checkout+ on this pool.
      def checkin(conn)
        @connection_mutex.synchronize do
          conn.send(:_run_checkin_callbacks) do
            @checked_out.delete conn
            @queue.signal
          end
        end
      end

      synchronize :clear_reloadable_connections!, :verify_active_connections!,
        :connected?, :disconnect!, :with => :@connection_mutex

      private
      def new_connection
        ActiveRecord::Base.send(spec.adapter_method, spec.config)
      end

      def current_connection_id #:nodoc:
        Thread.current.object_id
      end

      def checkout_new_connection
        c = new_connection
        @connections << c
        checkout_and_verify(c)
      end

      def checkout_existing_connection
        c = (@connections - @checked_out).first
        checkout_and_verify(c)
      end

      def checkout_and_verify(c)
        c.run_callbacks :checkout do
          c.verify!
          @checked_out << c
        end
        c
      end
    end

    # ConnectionHandler is a collection of ConnectionPool objects. It is used
    # for keeping separate connection pools for Active Record models that connect
    # to different databases.
    #
    # For example, suppose that you have 5 models, with the following hierarchy:
    #
    # |
    # +-- Book
    # | |
    # | +-- ScaryBook
    # | +-- GoodBook
    # +-- Author
    # +-- BankAccount
    #
    # Suppose that Book is to connect to a separate database (i.e. one other
    # than the default database). Then Book, ScaryBook and GoodBook will all use
    # the same connection pool. Likewise, Author and BankAccount will use the
    # same connection pool. However, the connection pool used by Author/BankAccount
    # is not the same as the one used by Book/ScaryBook/GoodBook.
    #
    # Normally there is only a single ConnectionHandler instance, accessible via
    # ActiveRecord::Base.connection_handler. Active Record models use this to
    # determine that connection pool that they should use.
    class ConnectionHandler
      attr_reader :connection_pools

      def initialize(pools = {})
        @connection_pools = pools
      end

      def establish_connection(name, spec)
        @connection_pools[name] = ConnectionAdapters::ConnectionPool.new(spec)
      end

      # Returns any connections in use by the current thread back to the pool,
      # and also returns connections to the pool cached by threads that are no
      # longer alive.
      def clear_active_connections!
        @connection_pools.each_value {|pool| pool.release_connection }
      end

      # Clears the cache which maps classes
      def clear_reloadable_connections!
        @connection_pools.each_value {|pool| pool.clear_reloadable_connections! }
      end

      def clear_all_connections!
        @connection_pools.each_value {|pool| pool.disconnect! }
      end

      # Verify active connections.
      def verify_active_connections! #:nodoc:
        @connection_pools.each_value {|pool| pool.verify_active_connections! }
      end

      # Locate the connection of the nearest super class. This can be an
      # active or defined connection: if it is the latter, it will be
      # opened and set as the active connection for the class it was defined
      # for (not necessarily the current class).
      def retrieve_connection(klass) #:nodoc:
        pool = retrieve_connection_pool(klass)
        (pool && pool.connection) or raise ConnectionNotEstablished
      end

      # Returns true if a connection that's accessible to this class has
      # already been opened.
      def connected?(klass)
        conn = retrieve_connection_pool(klass)
        conn && conn.connected?
      end

      # Remove the connection for this class. This will close the active
      # connection and the defined connection (if they exist). The result
      # can be used as an argument for establish_connection, for easily
      # re-establishing the connection.
      def remove_connection(klass)
        pool = @connection_pools[klass.name]
        return nil unless pool

        @connection_pools.delete_if { |key, value| value == pool }
        pool.disconnect!
        pool.spec.config
      end

      def retrieve_connection_pool(klass)
        pool = @connection_pools[klass.name]
        return pool if pool
        return nil if ActiveRecord::Base == klass
        retrieve_connection_pool klass.superclass
      end
    end

    class ConnectionManagement
      def initialize(app)
        @app = app
      end

      def call(env)
        @app.call(env)
      ensure
        # Don't return connection (and perform implicit rollback) if
        # this request is a part of integration test
        unless env.key?("rack.test")
          ActiveRecord::Base.clear_active_connections!
        end
      end
    end
  end
end
Something went wrong with that request. Please try again.