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Move XCB event handling into xcb_prepare_cb.

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Previously, we used ev_check watchers, which are executed at the beginning of an
event loop iteration.

This was problematic if one of the handlers happened to fill the XCB event
queue, e.g. by reading a reply from X11 and an event happened in the meantime.

In that situation, we would hand control to the event loop, entirely ignoring
the pending event. This would manifest itself as a 1-minute hang,
reproducible (sometimes) in the i3 testsuite.

issue #2790 describes an instance of this issue in i3bar, and we fixed that by
changing the watcher priority to run last. Handling events in xcb_prepare_cb has
the same effect, as ev_prepare watchers are run just before the event loop goes
to sleep.
This commit is contained in:
Michael Stapelberg
2017-10-03 10:03:29 +02:00
parent 1946cc6cab
commit 0d8b6714e3
4 changed files with 31 additions and 64 deletions
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16
src/floating.c
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@ -667,7 +667,7 @@ void floating_resize_window(Con *con, const bool proportional,
/* Custom data structure used to track dragging-related events. */
struct drag_x11_cb {
ev_check check;
ev_prepare prepare;
/* Whether this modal event loop should be exited and with which result. */
drag_result_t result;
@ -686,7 +686,7 @@ struct drag_x11_cb {
const void *extra;
};
static void xcb_drag_check_cb(EV_P_ ev_check *w, int revents) {
static void xcb_drag_prepare_cb(EV_P_ ev_prepare *w, int revents) {
struct drag_x11_cb *dragloop = (struct drag_x11_cb *)w->data;
xcb_motion_notify_event_t *last_motion_notify = NULL;
xcb_generic_event_t *event;
@ -765,6 +765,8 @@ static void xcb_drag_check_cb(EV_P_ ev_check *w, int revents) {
dragloop->extra);
}
free(last_motion_notify);
xcb_flush(conn);
}
/*
@ -831,18 +833,18 @@ drag_result_t drag_pointer(Con *con, const xcb_button_press_event_t *event, xcb_
.callback = callback,
.extra = extra,
};
ev_check *check = &loop.check;
ev_prepare *prepare = &loop.prepare;
if (con)
loop.old_rect = con->rect;
ev_check_init(check, xcb_drag_check_cb);
check->data = &loop;
ev_prepare_init(prepare, xcb_drag_prepare_cb);
prepare->data = &loop;
main_set_x11_cb(false);
ev_check_start(main_loop, check);
ev_prepare_start(main_loop, prepare);
while (loop.result == DRAGGING)
ev_run(main_loop, EVRUN_ONCE);
ev_check_stop(main_loop, check);
ev_prepare_stop(main_loop, prepare);
main_set_x11_cb(true);
xcb_ungrab_keyboard(conn, XCB_CURRENT_TIME);