From 7d2d3958d5eedf5bf677a30dfd3e1dfb108474b3 Mon Sep 17 00:00:00 2001
From: Povilas Kanapickas <povilas@radix.lt>
Date: Wed, 20 May 2020 22:11:14 +0300
Subject: [PATCH] XWindowsEventQueueBuffer: Fix delays when waiting for new
 events

QLength() may return 0 even if there are events pending because they
need to be read from the display socket in order to become visible. We
must use XPending() which will poll the socket if QLength() == 0.
---
 src/lib/platform/XWindowsEventQueueBuffer.cpp | 8 +++++++-
 src/lib/platform/XWindowsEventQueueBuffer.h   | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/lib/platform/XWindowsEventQueueBuffer.cpp b/src/lib/platform/XWindowsEventQueueBuffer.cpp
index 78f0e5af863..6c97c7edfd7 100644
--- a/src/lib/platform/XWindowsEventQueueBuffer.cpp
+++ b/src/lib/platform/XWindowsEventQueueBuffer.cpp
@@ -82,6 +82,12 @@ XWindowsEventQueueBuffer::~XWindowsEventQueueBuffer()
     close(m_pipefd[1]);
 }
 
+int XWindowsEventQueueBuffer::getPendingCountLocked()
+{
+    Lock lock(&m_mutex);
+    return XPending(m_display);
+}
+
 void
 XWindowsEventQueueBuffer::waitForEvent(double dtimeout)
 {
@@ -163,7 +169,7 @@ XWindowsEventQueueBuffer::waitForEvent(double dtimeout)
     // we want to give the cpu a chance s owe up this to 25ms
 #define TIMEOUT_DELAY 25
 
-    while (((dtimeout < 0.0) || (remaining > 0)) && QLength(m_display)==0 && retval==0){
+    while (((dtimeout < 0.0) || (remaining > 0)) && getPendingCountLocked() == 0 && retval == 0) {
 #if HAVE_POLL
     retval = poll(pfds, 2, TIMEOUT_DELAY); //16ms = 60hz, but we make it > to play nicely with the cpu
      if (pfds[1].revents & POLLIN) {
diff --git a/src/lib/platform/XWindowsEventQueueBuffer.h b/src/lib/platform/XWindowsEventQueueBuffer.h
index e49b282b05d..13f6b160d42 100644
--- a/src/lib/platform/XWindowsEventQueueBuffer.h
+++ b/src/lib/platform/XWindowsEventQueueBuffer.h
@@ -51,6 +51,8 @@ class XWindowsEventQueueBuffer : public IEventQueueBuffer {
 private:
     void                flush();
 
+    int getPendingCountLocked();
+
 private:
     typedef std::vector<XEvent> EventList;
      IXWindowsImpl*       m_impl;