method

checkout

v3.2.8 - Show latest stable - Class: ActiveRecord::ConnectionAdapters::ConnectionPool

checkout()

public

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.

# File activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb, line 232
      def checkout
        synchronize do
          waited_time = 0

          loop do
            conn = @connections.find { |c| c.lease }

            unless conn
              if @connections.size < @size
                conn = checkout_new_connection
                conn.lease
              end
            end

            if conn
              checkout_and_verify conn
              return conn
            end

            if waited_time >= @timeout
              raise ConnectionTimeoutError, "could not obtain a database connection#{" within #{@timeout} seconds" if @timeout} (waited #{waited_time} seconds). The max pool size is currently #{@size}; consider increasing it."
            end

            # Sometimes our wait can end because a connection is available,
            # but another thread can snatch it up first. If timeout hasn't
            # passed but no connection is avail, looks like that happened --
            # loop and wait again, for the time remaining on our timeout. 
            before_wait = Time.now
            @queue.wait( [@timeout - waited_time, 0].max )
            waited_time += (Time.now - before_wait)

            # Will go away in Rails 4, when we don't clean up
            # after leaked connections automatically anymore. Right now, clean
            # up after we've returned from a 'wait' if it looks like it's
            # needed, then loop and try again. 
            if(active_connections.size >= @connections.size)
              clear_stale_cached_connections!
            end
          end
        end
      end

checkout

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