Add synchronization to connection pool also

activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb

@@ -12,6 +12,9 @@ module ActiveRecord
 
         # The ConnectionSpecification for this pool
         @spec = spec
+
+        # The mutex used to synchronize pool access
+        @connection_mutex = Monitor.new
       end
 
       def active_connection_name #:nodoc:
@@ -70,7 +73,7 @@ module ActiveRecord
           # Verify the connection.
           conn.verify!(verification_timeout)
         else
-          self.connection = spec
+          self.set_connection spec
           conn = active_connections[name]
         end
 
@@ -82,6 +85,7 @@ module ActiveRecord
         active_connections[active_connection_name] ? true : false
       end
 
+      # Disconnect all connections in the pool.
       def disconnect!
         clear_cache!(@active_connections) do |name, conn|
           conn.disconnect!
@@ -89,16 +93,20 @@ module ActiveRecord
       end
 
       # Set the connection for the class.
-      def connection=(spec) #:nodoc:
+      def set_connection(spec) #:nodoc:
         if spec.kind_of?(ActiveRecord::ConnectionAdapters::AbstractAdapter)
           active_connections[active_connection_name] = spec
         elsif spec.kind_of?(ActiveRecord::Base::ConnectionSpecification)
-          self.connection = ActiveRecord::Base.send(spec.adapter_method, spec.config)
+          self.set_connection ActiveRecord::Base.send(spec.adapter_method, spec.config)
         else
           raise ConnectionNotEstablished
         end
       end
 
+      synchronize :active_connection, :connection, :clear_active_connections!,
+        :clear_reloadable_connections!, :verify_active_connections!, :retrieve_connection,
+        :connected?, :disconnect!, :set_connection, :with => :@connection_mutex
+
       private
         def clear_cache!(cache, &block)
           cache.each(&block) if block_given?

activerecord/lib/active_record/connection_adapters/abstract/connection_specification.rb

@@ -27,6 +27,8 @@ module ActiveRecord
     @@connection_pools = {}
 
     class << self
+      # Turning on allow_concurrency basically switches a null mutex for a real one, so that
+      # multi-threaded access of the connection pools hash is synchronized.
       def allow_concurrency=(flag)
         if @@allow_concurrency != flag
           if flag
@@ -37,7 +39,7 @@ module ActiveRecord
         end
       end
 
-      # for internal use only
+      # for internal use only and for testing
       def active_connections #:nodoc:
         @@connection_pools.inject({}) do |hash,kv|
           hash[kv.first] = kv.last.active_connection

activesupport/lib/active_support/core_ext/module/synchronization.rb

@@ -18,7 +18,7 @@ class Module
       raise ArgumentError, "Synchronization needs a mutex. Supply an options hash with a :with key as the last argument (e.g. synchronize :hello, :with => :@mutex)."
     end
 
-    methods.each do |method|
+    methods.flatten.each do |method|
       aliased_method, punctuation = method.to_s.sub(/([?!=])$/, ''), $1
       if instance_methods.include?("#{aliased_method}_without_synchronization#{punctuation}")
         raise ArgumentError, "#{method} is already synchronized. Double synchronization is not currently supported."
@@ -26,7 +26,7 @@ class Module
       module_eval(<<-EOS, __FILE__, __LINE__)
         def #{aliased_method}_with_synchronization#{punctuation}(*args, &block)
           #{with}.synchronize do
-            #{aliased_method}_without_synchronization#{punctuation}(*args,&block)
+            #{aliased_method}_without_synchronization#{punctuation}(*args, &block)
           end
         end
       EOS