make active_connection? return true only if there is an open connecti…

…on in use for the current thread. fixes rails#5330

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

@@ -95,10 +95,11 @@ def connection
         @reserved_connections[current_connection_id] ||= checkout
       end
 
-      # Check to see if there is an active connection in this connection
-      # pool.
+      # Is there an open connection that is being used for the current thread?
       def active_connection?
-        active_connections.any?
+        @reserved_connections.fetch(current_connection_id) {
+          return false
+        }.in_use?
       end
 
       # Signal that the thread is finished with the current connection.

activerecord/test/cases/connection_pool_test.rb

@@ -3,7 +3,11 @@
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionPoolTest < ActiveRecord::TestCase
+      attr_reader :pool
+
       def setup
+        super
+
         # Keep a duplicate pool so we do not bother others
         @pool = ConnectionPool.new ActiveRecord::Base.connection_pool.spec
 
@@ -18,6 +22,44 @@ def setup
         end
       end
 
+      def teardown
+        super
+        @pool.disconnect!
+      end
+
+      def active_connections(pool)
+        pool.connections.find_all(&:in_use?)
+      end
+
+      def test_with_connection
+        assert_equal 0, active_connections(pool).size
+
+        main_thread = pool.connection
+        assert_equal 1, active_connections(pool).size
+
+        Thread.new {
+          pool.with_connection do |conn|
+            assert conn
+            assert_equal 2, active_connections(pool).size
+          end
+          assert_equal 1, active_connections(pool).size
+        }.join
+
+        main_thread.close
+        assert_equal 0, active_connections(pool).size
+      end
+
+      def test_active_connection_in_use
+        assert !pool.active_connection?
+        main_thread = pool.connection
+
+        assert pool.active_connection?
+
+        main_thread.close
+
+        assert !pool.active_connection?
+      end
+
       def test_active_connection?
         assert !@pool.active_connection?
         assert @pool.connection