connections can be reaped via the `reap` method

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

@@ -232,6 +232,18 @@ def remove(conn)
         end
       end
 
+      # Removes dead connections from the pool.  A dead connection can occur
+      # if a programmer forgets to close a connection at the end of a thread
+      # or a thread dies unexpectedly.
+      def reap
+        synchronize do
+          stale = Time.now - @timeout
+          connections.dup.each do |conn|
+            remove conn if conn.in_use? && stale > conn.last_use
+          end
+        end
+      end
+
       private
 
       def new_connection

activerecord/test/cases/connection_pool_test.rb

@@ -25,6 +25,21 @@ def teardown
         @pool.connections.each(&:close)
       end
 
+      def test_reap
+        @pool.checkout
+        @pool.checkout
+        @pool.checkout
+        @pool.timeout = 0
+
+        connections = @pool.connections.dup
+
+        @pool.reap
+
+        assert_equal 0, @pool.connections.length
+      ensure
+        connections.map(&:close)
+      end
+
       def test_remove_connection
         conn = @pool.checkout
         assert conn.in_use?