React to sql driver process exit earlier

If there are queued request when connection closes we may try to process
those requests (by trying to send them to already terminated db process,
and waiting until we hit timeout) before we see that driver is not longer
alive. This change adds check for driver exit before we process next
queued sql request, and immediately switch to connection state if we have
one.

src/ejabberd_sql.erl

@@ -483,9 +483,16 @@ run_sql_cmd(Command, From, State, Timestamp) ->
 	    State1 = report_overload(State),
 	    {next_state, session_established, State1};
 	false ->
-	    put(?NESTING_KEY, ?TOP_LEVEL_TXN),
-	    put(?STATE_KEY, State),
-	    abort_on_driver_error(outer_op(Command), From, Timestamp)
+	    receive
+		{'EXIT', _Pid, Reason} ->
+		    PR = p1_queue:in({sql_cmd, Command, From, Timestamp},
+				     State#state.pending_requests),
+		    handle_reconnect(Reason, State#state{pending_requests = PR})
+	    after 0 ->
+		put(?NESTING_KEY, ?TOP_LEVEL_TXN),
+		put(?STATE_KEY, State),
+		abort_on_driver_error(outer_op(Command), From, Timestamp)
+	    end
     end.
 
 %% @doc Only called by handle_call, only handles top level operations.
@@ -670,11 +677,10 @@ sql_query_internal(Query) ->
 		pgsql_to_odbc(pgsql:squery(State#state.db_ref, Query,
 					   QueryTimeout - 1000));
 	    mysql ->
-		R = mysql_to_odbc(p1_mysql_conn:squery(State#state.db_ref,
+		mysql_to_odbc(p1_mysql_conn:squery(State#state.db_ref,
 						   [Query], self(),
-						   [{timeout, QueryTimeout - 1000},
-						    {result_type, binary}])),
-		  R;
+						   [{QueryTimeout - 1000},
+						    {result_type, binary}]));
 	      sqlite ->
 		  Host = State#state.host,
 		  sqlite_to_odbc(Host, sqlite3:sql_exec(sqlite_db(Host), Query))
@@ -854,7 +860,6 @@ sql_rollback() ->
       [{mssql, [<<"rollback transaction;">>]},
        {any, [<<"rollback;">>]}]).
 
-
 %% Generate the OTP callback return tuple depending on the driver result.
 abort_on_driver_error({error, <<"query timed out">>} = Reply, From, Timestamp) ->
     reply(From, Reply, Timestamp),