fix ruby 1.9 deadlock problem, fixes #5736 add connection pool tests

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

@@ -75,10 +75,7 @@ def initialize(spec)
         @queue = @connection_mutex.new_cond
 
         # default 5 second timeout unless on ruby 1.9
-        @timeout =
-          if RUBY_VERSION < '1.9'
-            spec.config[:wait_timeout] || 5
-          end
+        @timeout = spec.config[:wait_timeout] || 5
 
         # default max pool size to 5
         @size = (spec.config[:pool] && spec.config[:pool].to_i) || 5
@@ -161,7 +158,6 @@ 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)
@@ -194,16 +190,18 @@ def checkout
                      checkout_new_connection
                    end
             return conn if conn
-            # No connections available; wait for one
-            if @queue.wait(@timeout)
+
+            @queue.wait(@timeout)
+
+            if(@checked_out.size < @connections.size)
               next
             else
-              # try looting dead threads
               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

activerecord/test/cases/connection_pool_test.rb

@@ -26,6 +26,35 @@ def checkin conn
                "threads should have been removed")
         assert_equal pool.checkins.length, threads.length
       end
+
+      def test_checkout_behaviour
+        pool = ConnectionPool.new ActiveRecord::Base.connection_pool.spec
+        connection = pool.connection
+        assert_not_nil connection
+        threads = []
+        4.times do |i|
+          threads << Thread.new(i) do |pool_count|
+            connection = pool.connection
+            assert_not_nil connection
+          end
+        end
+
+        threads.each {|t| t.join}
+
+        Thread.new do
+          threads.each do |t|
+            thread_ids = pool.instance_variable_get(:@reserved_connections).keys
+            assert thread_ids.include?(t.object_id)
+          end
+
+          pool.connection
+          threads.each do |t|
+            thread_ids = pool.instance_variable_get(:@reserved_connections).keys
+            assert !thread_ids.include?(t.object_id)
+          end
+        end.join()
+
+      end
     end
   end
 end