From 5519447b9db4023deca98e5b882845416a9c33f1 Mon Sep 17 00:00:00 2001 From: Sheng Mao Date: Fri, 13 Nov 2020 22:34:46 -0700 Subject: [PATCH] Let QXcbConnection::getTimestamp properly exit when X server quits MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit QXcbConnection::getTimestamp uses dummy events to get timestamp from X server. However, in some cases, X server shuts down while client tries to get timestamp. In this case, QXcbConnection::getTimestamp keeps getting null event and thus falls into indefinite loop. This fix checks if xcb connection is still valid and use a special xcb_timestamp_t value, CurrentTime (0L), as returned value. CurrentTime should not be generated by X server and if getTimestamp returns this value, it means an "exception" case is triggered. This fix is introduced because in kwin_x11 (KDE project), X server can exit on logout. kwin_x11 should handle disconnection from X server. But the indefinite loop prevents kwin_x11 to process disconnection event and therefore kwin_x11 cannot quit properly. Fixes: QTBUG-88435 Change-Id: Iaf7ef3f8a35fa8389d22a608e3c49041bf90e1b9 Reviewed-by: Qt CI Bot Reviewed-by: Liang Qi Reviewed-by: Tor Arne Vestbø (cherry picked from commit dbd1c8b047700bb6d0adae848d6cbb89fa2fcfff) Reviewed-by: Qt Cherry-pick Bot --- src/plugins/platforms/xcb/qxcbconnection.cpp | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/src/plugins/platforms/xcb/qxcbconnection.cpp b/src/plugins/platforms/xcb/qxcbconnection.cpp index c557109bd1..9abdae6a7c 100644 --- a/src/plugins/platforms/xcb/qxcbconnection.cpp +++ b/src/plugins/platforms/xcb/qxcbconnection.cpp @@ -763,7 +763,10 @@ xcb_timestamp_t QXcbConnection::getTimestamp() xcb_generic_event_t *event = nullptr; - while (!event) { + // When disconnection is caused by X server, event will never be able to hold + // a valid pointer. isConnected(), which calls xcb_connection_has_error(), + // can handle this type of disconnection and properly quits the loop. + while (isConnected() && !event) { connection()->sync(); event = eventQueue()->peek([window, dummyAtom](xcb_generic_event_t *event, int type) { if (type != XCB_PROPERTY_NOTIFY) @@ -773,6 +776,14 @@ xcb_timestamp_t QXcbConnection::getTimestamp() }); } + if (!event) { + // https://www.x.org/releases/X11R7.7/doc/xproto/x11protocol.html#glossary + // > One timestamp value (named CurrentTime) is never generated by the + // > server. This value is reserved for use in requests to represent the + // > current server time. + return XCB_CURRENT_TIME; + } + xcb_property_notify_event_t *pn = reinterpret_cast(event); xcb_timestamp_t timestamp = pn->time; free(event); -- 2.30.0