From 748ca81d4b71ef3127a939655080c9072f791fd7 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Thu, 23 Jan 2020 15:07:22 +0530
Subject: [PATCH] Wayland: Fix a freeze in rare circumstances when having
 multiple OS Windows

Fixes #2307
Fixes #1722
---
 docs/changelog.rst   |  3 +++
 glfw/backend_utils.c |  4 +++-
 glfw/backend_utils.h |  2 +-
 glfw/wl_window.c     | 16 ++++++++++------
 glfw/x11_window.c    |  2 +-
 5 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 2a38fb3fd..74482920d 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -19,6 +19,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 - Allow choosing OpenType features for individual fonts via the
   :opt:`font_features` option. (:pull:`2248`)
 
+- Wayland: Fix a freeze in rare circumstances when having multiple OS Windows
+  (:iss:`2307` and :iss:`1722`)
+
 - Add an option :opt:`force_ltr` to turn off the display of text in RTL scripts
   in right-to-left order (:pull:`2293`)
 
diff --git a/glfw/backend_utils.c b/glfw/backend_utils.c
index 2a0f6fd7b..ad76bbb1c 100644
--- a/glfw/backend_utils.c
+++ b/glfw/backend_utils.c
@@ -292,7 +292,7 @@ finalizePollData(EventLoopData *eld) {
 }
 
 int
-pollForEvents(EventLoopData *eld, monotonic_t timeout) {
+pollForEvents(EventLoopData *eld, monotonic_t timeout, watch_callback_func display_callback) {
     int read_ok = 0;
     timeout = prepareForPoll(eld, timeout);
     EVDBG("pollForEvents final timeout: %.3f", monotonic_t_to_s_double(timeout));
@@ -305,6 +305,7 @@ pollForEvents(EventLoopData *eld, monotonic_t timeout) {
             errno = 0;
             result = pollWithTimeout(eld->fds, eld->watches_count, timeout);
             int saved_errno = errno;
+            if (display_callback) display_callback(result, eld->fds[0].revents && eld->watches[0].events, NULL);
             dispatchTimers(eld);
             if (result > 0) {
                 dispatchEvents(eld);
@@ -319,6 +320,7 @@ pollForEvents(EventLoopData *eld, monotonic_t timeout) {
             errno = 0;
             result = poll(eld->fds, eld->watches_count, -1);
             int saved_errno = errno;
+            if (display_callback) display_callback(result, eld->fds[0].revents && eld->watches[0].events, NULL);
             dispatchTimers(eld);
             if (result > 0) {
                 dispatchEvents(eld);
diff --git a/glfw/backend_utils.h b/glfw/backend_utils.h
index 3e1ff2abe..cb92dc7b3 100644
--- a/glfw/backend_utils.h
+++ b/glfw/backend_utils.h
@@ -90,7 +90,7 @@ void toggleTimer(EventLoopData *eld, id_type timer_id, int enabled);
 void changeTimerInterval(EventLoopData *eld, id_type timer_id, monotonic_t interval);
 monotonic_t prepareForPoll(EventLoopData *eld, monotonic_t timeout);
 int pollWithTimeout(struct pollfd *fds, nfds_t nfds, monotonic_t timeout);
-int pollForEvents(EventLoopData *eld, monotonic_t timeout);
+int pollForEvents(EventLoopData *eld, monotonic_t timeout, watch_callback_func);
 unsigned dispatchTimers(EventLoopData *eld);
 void finalizePollData(EventLoopData *eld);
 bool initPollData(EventLoopData *eld, int display_fd);
diff --git a/glfw/wl_window.c b/glfw/wl_window.c
index 154688420..5c7aa0c09 100644
--- a/glfw/wl_window.c
+++ b/glfw/wl_window.c
@@ -754,6 +754,13 @@ abortOnFatalError(int last_error) {
     _glfw.wl.eventLoopData.wakeup_data_read = true;
 }
 
+static void
+wayland_read_events(int poll_result, int events, void *data UNUSED) {
+    EVDBG("wayland_read_events poll_result: %d events: %d", poll_result, events);
+    if (poll_result > 0 && events) wl_display_read_events(_glfw.wl.display);
+    else wl_display_cancel_read(_glfw.wl.display);
+}
+
 static void
 handleEvents(monotonic_t timeout)
 {
@@ -779,18 +786,15 @@ handleEvents(monotonic_t timeout)
         return;
     }
 
-    bool display_read_ok = pollForEvents(&_glfw.wl.eventLoopData, timeout);
+    // we pass in wayland_read_events to ensure that the above wl_display_prepare_read call
+    // is followed by either wl_display_cancel_read or wl_display_read_events
+    bool display_read_ok = pollForEvents(&_glfw.wl.eventLoopData, timeout, wayland_read_events);
     EVDBG("display_read_ok: %d", display_read_ok);
     if (display_read_ok) {
-        wl_display_read_events(display);
         int num = wl_display_dispatch_pending(display);
         (void)num;
         EVDBG("dispatched %d Wayland events", num);
     }
-    else
-    {
-        wl_display_cancel_read(display);
-    }
     glfw_ibus_dispatch(&_glfw.wl.xkb.ibus);
     glfw_dbus_session_bus_dispatch();
     EVDBG("other dispatch done");
diff --git a/glfw/x11_window.c b/glfw/x11_window.c
index 7cb1c3ace..102749ead 100644
--- a/glfw/x11_window.c
+++ b/glfw/x11_window.c
@@ -68,7 +68,7 @@ static unsigned _glfwDispatchX11Events(void);
 static void
 handleEvents(monotonic_t timeout) {
     EVDBG("starting handleEvents(%.2f)", monotonic_t_to_s_double(timeout));
-    int display_read_ok = pollForEvents(&_glfw.x11.eventLoopData, timeout);
+    int display_read_ok = pollForEvents(&_glfw.x11.eventLoopData, timeout, NULL);
     EVDBG("display_read_ok: %d", display_read_ok);
     if (display_read_ok) {
         unsigned dispatched = _glfwDispatchX11Events();