Revert "backport fair connection pool 02b2335563 to 3-2-stable"

This reverts commit 0693e079708a52b777f2b7872b8e3d467b880a0d.

Revert "Cache columns metadata to avoid extra while testing"

This reverts commit a82f1e3f5d11c8dfba9f4c911745ec40a7965216.

Reason: This is causing failures in the postgresql build.
See http://travis-ci.org/#!/rails/rails/builds/2485584

Related with #7675

1 files changed, 49 insertions, 190 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 235efc12f6..d4649102df 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -57,141 +57,10 @@ module ActiveRecord
     # * +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
-
-      # Threadsafe, fair, FIFO queue.  Meant to be used by ConnectionPool
-      # with which it shares a Monitor.  But could be a generic Queue.
-      #
-      # The Queue in stdlib's 'thread' could replace this class except
-      # stdlib's doesn't support waiting with a timeout.
-      class Queue
-        def initialize(lock = Monitor.new)
-          @lock = lock
-          @cond = @lock.new_cond
-          @num_waiting = 0
-          @queue = []
-        end
-
-        # Test if any threads are currently waiting on the queue.
-        def any_waiting?
-          synchronize do
-            @num_waiting > 0
-          end
-        end
-
-        # Return the number of threads currently waiting on this
-        # queue.
-        def num_waiting
-          synchronize do
-            @num_waiting
-          end
-        end
-
-        # Add +element+ to the queue.  Never blocks.
-        def add(element)
-          synchronize do
-            @queue.push element
-            @cond.signal
-          end
-        end
-
-        # If +element+ is in the queue, remove and return it, or nil.
-        def delete(element)
-          synchronize do
-            @queue.delete(element)
-          end
-        end
-
-        # Remove all elements from the queue.
-        def clear
-          synchronize do
-            @queue.clear
-          end
-        end
-
-        # Remove the head of the queue.
-        #
-        # If +timeout+ is not given, remove and return the head the
-        # queue if the number of available elements is strictly
-        # greater than the number of threads currently waiting (that
-        # is, don't jump ahead in line).  Otherwise, return nil.
-        #
-        # If +timeout+ is given, block if it there is no element
-        # available, waiting up to +timeout+ seconds for an element to
-        # become available.
-        #
-        # Raises:
-        # - ConnectionTimeoutError if +timeout+ is given and no element
-        # becomes available after +timeout+ seconds,
-        def poll(timeout = nil)
-          synchronize do
-            if timeout
-              no_wait_poll || wait_poll(timeout)
-            else
-              no_wait_poll
-            end
-          end
-        end
-
-        private
-
-        def synchronize(&block)
-          @lock.synchronize(&block)
-        end
-
-        # Test if the queue currently contains any elements.
-        def any?
-          !@queue.empty?
-        end
-
-        # A thread can remove an element from the queue without
-        # waiting if an only if the number of currently available
-        # connections is strictly greater than the number of waiting
-        # threads.
-        def can_remove_no_wait?
-          @queue.size > @num_waiting
-        end
-
-        # Removes and returns the head of the queue if possible, or nil.
-        def remove
-          @queue.shift
-        end
-
-        # Remove and return the head the queue if the number of
-        # available elements is strictly greater than the number of
-        # threads currently waiting.  Otherwise, return nil.
-        def no_wait_poll
-          remove if can_remove_no_wait?
-        end
-
-        # Waits on the queue up to +timeout+ seconds, then removes and
-        # returns the head of the queue.
-        def wait_poll(timeout)
-          @num_waiting += 1
-
-          t0 = Time.now
-          elapsed = 0
-          loop do
-            @cond.wait(timeout - elapsed)
-
-            return remove if any?
-
-            elapsed = Time.now - t0
-
-            if elapsed >= timeout
-              msg = 'could not obtain a database connection within %0.3f seconds (waited %0.3f seconds)' %
-                [timeout, elapsed]
-              raise ConnectionTimeoutError, msg
-            end
-          end
-        ensure
-          @num_waiting -= 1
-        end
-      end
-
       include MonitorMixin
 
       attr_accessor :automatic_reconnect
-      attr_reader :spec, :connections, :size
+      attr_reader :spec, :connections
 
       # Creates a new ConnectionPool object. +spec+ is a ConnectionSpecification
       # object which describes database connection information (e.g. adapter,
@@ -207,6 +76,7 @@ module ActiveRecord
         # The cache of reserved connections mapped to threads
         @reserved_connections = {}
 
+        @queue = new_cond
         @timeout = spec.config[:wait_timeout] || 5
 
         # default max pool size to 5
@@ -214,16 +84,6 @@ module ActiveRecord
 
         @connections         = []
         @automatic_reconnect = true
-
-        @available = Queue.new self
-      end
-
-      # Hack for tests to be able to add connections.  Do not call outside of tests
-      def insert_connection_for_test!(c) #:nodoc:
-        synchronize do
-          @connections << c
-          @available.add c
-        end
       end
 
       # Retrieve the connection associated with the current thread, or call
@@ -279,7 +139,6 @@ module ActiveRecord
             conn.disconnect!
           end
           @connections = []
-          @available.clear
         end
       end
 
@@ -291,15 +150,9 @@ module ActiveRecord
             checkin conn
             conn.disconnect! if conn.requires_reloading?
           end
-
           @connections.delete_if do |conn|
             conn.requires_reloading?
           end
-          @available.clear
-          @connections.each do |conn|
-            @available.add conn
-          end
-          
         end
       end
 
@@ -363,22 +216,58 @@ connection.  For example: ActiveRecord::Base.connection.close
       # 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 and leasing existing connection, or by
-      # creating a new connection and leasing it.
-      #
-      # If all connections are leased and the pool is at capacity (meaning the
-      # number of currently leased connections is greater than or equal to the
-      # size limit set), an ActiveRecord::PoolFullError exception will be raised.
+      # 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:
-      # - PoolFullError: no connection can be obtained from the pool.
+      # - ConnectionTimeoutError: no connection can be obtained from the pool
+      #   within the timeout period.
       def checkout
         synchronize do
-          conn = acquire_connection
-          conn.lease
-          checkout_and_verify(conn)
+          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
 
@@ -391,40 +280,10 @@ connection.  For example: ActiveRecord::Base.connection.close
         synchronize do
           conn.run_callbacks :checkin do
             conn.expire
+            @queue.signal
           end
 
           release conn
-
-          @available.add conn
-        end
-      end
-
-      # Acquire a connection by one of 1) immediately removing one
-      # from the queue of available connections, 2) creating a new
-      # connection if the pool is not at capacity, 3) waiting on the
-      # queue for a connection to become available (first calling
-      # clear_stale_cached_connections! to clean up leaked connections,
-      # this cleanup will prob be going away in Rails4).
-      #
-      # Raises:
-      # - ConnectionTimeoutError if a connection could not be acquired
-      def acquire_connection
-        if conn = @available.poll
-          conn
-        elsif @connections.size < @size
-          checkout_new_connection
-        else
-          # this conditional clear_stale 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 before trying to wait for a connection.
-          synchronize do
-            if(active_connections.size >= @connections.size)
-              clear_stale_cached_connections!
-            end
-          end
-
-          @available.poll(@timeout)
         end
       end