Ensure that all the transactions should be canceled before closing the connections when a server is disconnected using pgAdmin. Fixes #5142

docs/en_US/release_notes_4_19.rst

@@ -30,6 +30,7 @@ Bug fixes
 | `Issue #5077 <https://redmine.postgresql.org/issues/5077>`_ -  Changed background pattern for geometry viewer to use #fff for all themes.
 | `Issue #5107 <https://redmine.postgresql.org/issues/5107>`_ -  Set proper focus on tab navigation for file manager dialog.
 | `Issue #5115 <https://redmine.postgresql.org/issues/5115>`_ -  Fix an issue where command and statements were parsed incorrectly for Rules.
+| `Issue #5142 <https://redmine.postgresql.org/issues/5142>`_ -  Ensure that all the transactions should be canceled before closing the connections when a server is disconnected using pgAdmin.
 | `Issue #5143 <https://redmine.postgresql.org/issues/5143>`_ -  Fix accessibility issue for the maximize button of the Alertify dialog.
 | `Issue #5184 <https://redmine.postgresql.org/issues/5184>`_ -  Fixed Firefox monospaced issue by updating the font to the latest version.
 | `Issue #5214 <https://redmine.postgresql.org/issues/5214>`_ -  Update Flask-SQLAlchemy and SQLAlchemy package which is not working on Windows with Python 3.8.

web/pgadmin/utils/driver/psycopg2/connection.py

@@ -1460,6 +1460,16 @@ Failed to reset the connection to the server due to following error:
                 )
             errmsg = self._formatted_exception_msg(pe, formatted_exception_msg)
             is_error = True
+        except OSError as e:
+            # Bad File descriptor
+            if e.errno == 9:
+                raise ConnectionLost(
+                    self.manager.sid,
+                    self.db,
+                    self.conn_id[5:]
+                )
+            else:
+                raise e
 
         if self.conn.notices and self.__notices is not None:
             self.__notices.extend(self.conn.notices)
@@ -1648,8 +1658,13 @@ Failed to reset the connection to the server due to following error:
         Returns the list of the messages/notices send from the database server.
         """
         resp = []
-        while self.__notices:
-            resp.append(self.__notices.pop(0))
+
+        if self.__notices is not None:
+            while self.__notices:
+                resp.append(self.__notices.pop(0))
+
+        if self.__notifies is None:
+            return resp
 
         for notify in self.__notifies:
             if notify.payload is not None and notify.payload != '':

web/pgadmin/utils/driver/psycopg2/server_manager.py

@@ -403,8 +403,14 @@ WHERE db.oid = {0}""".format(did))
             else:
                 return False
 
-        for con in self.connections:
-            self.connections[con]._release()
+        for con_key in list(self.connections.keys()):
+            conn = self.connections[con_key]
+            # Cancel the ongoing transaction before closing the connection
+            # as it may hang forever
+            if conn.connected() and conn.conn_id is not None and \
+               conn.conn_id.startswith('CONN:'):
+                conn.cancel_transaction(conn.conn_id[5:])
+            conn._release()
 
         self.connections = dict()
         self.ver = None