From 95f2a840be42b7fb92317a14d04f4dd047405660 Mon Sep 17 00:00:00 2001
From: Vasily Galkin <galkin-vv@ya.ru>
Date: Wed, 6 May 2020 14:16:45 +0300
Subject: [PATCH] Windows 8+: make waiting for messages correspond to emptiness
 check

Fixes high cpu usage spikes on win10.
When queue was containing messages of only non-QS_POSTMESSAGE type the
"while (m_buffer->isEmpty())" busy-looped in EventQueue::getEvent
since isEmpty was true (checked only QS_POSTMESSAGE message type),
but waitForEvent returned immediately (checked more message types).

Investigation shows that the difference was introduced in
https://github.com/debauchee/barrier/commit/dbfb04a6e
to fix a problem with bad behaviour of GetQueueStatus
Researching showed that a similar problem was fixed in Qt,
and the solution was
"pass different flags to GetQueueStatus depending on version of windows"
https://bugreports.qt.io/browse/QTBUG-29097

So this patch makes changes to a barrier non-GUI core similar to Qt fix.
---
 src/lib/platform/MSWindowsEventQueueBuffer.cpp | 16 ++++++++++++----
 src/lib/platform/MSWindowsEventQueueBuffer.h   |  1 +
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/src/lib/platform/MSWindowsEventQueueBuffer.cpp b/src/lib/platform/MSWindowsEventQueueBuffer.cpp
index f6de1573..31113676 100644
--- a/src/lib/platform/MSWindowsEventQueueBuffer.cpp
+++ b/src/lib/platform/MSWindowsEventQueueBuffer.cpp
@@ -21,6 +21,7 @@
 #include "arch/win32/ArchMiscWindows.h"
 #include "mt/Thread.h"
 #include "base/IEventQueue.h"
+#include <VersionHelpers.h>
 
 //
 // EventQueueTimer
@@ -48,6 +49,15 @@ MSWindowsEventQueueBuffer::MSWindowsEventQueueBuffer(IEventQueue* events) :
     // make sure this thread has a message queue
     MSG dummy;
     PeekMessage(&dummy, NULL, WM_USER, WM_USER, PM_NOREMOVE);
+
+    m_os_supported_message_types = QS_ALLINPUT;
+    if (!IsWindows8OrGreater())
+    {
+        // don't use QS_POINTER, QS_TOUCH
+        // because they can cause GetQueueStatus() to always return 0 and we miss events
+        // since those flags are confusing Windows 7. See QTBUG-29097 for related info
+        m_os_supported_message_types &= ~(QS_TOUCH | QS_POINTER);
+    }
 }
 
 MSWindowsEventQueueBuffer::~MSWindowsEventQueueBuffer()
@@ -79,7 +89,7 @@ MSWindowsEventQueueBuffer::waitForEvent(double timeout)
     // cancellation but that's okay because we're run in the main
     // thread and we never cancel that thread.
     HANDLE dummy[1];
-    MsgWaitForMultipleObjects(0, dummy, FALSE, t, QS_ALLINPUT);
+    MsgWaitForMultipleObjects(0, dummy, FALSE, t, m_os_supported_message_types);
 }
 
 IEventQueueBuffer::Type
@@ -128,9 +138,7 @@ MSWindowsEventQueueBuffer::addEvent(UInt32 dataID)
 bool
 MSWindowsEventQueueBuffer::isEmpty() const
 {
-    // don't use QS_POINTER, QS_TOUCH, or any meta-flags that include them (like QS_ALLINPUT)
-    // because they can cause GetQueueStatus() to always return 0 and we miss events
-    return (HIWORD(GetQueueStatus(QS_POSTMESSAGE)) == 0);
+    return (HIWORD(GetQueueStatus(m_os_supported_message_types)) == 0);
 }
 
 EventQueueTimer*
diff --git a/src/lib/platform/MSWindowsEventQueueBuffer.h b/src/lib/platform/MSWindowsEventQueueBuffer.h
index 6a0f9f90..bc9bde1f 100644
--- a/src/lib/platform/MSWindowsEventQueueBuffer.h
+++ b/src/lib/platform/MSWindowsEventQueueBuffer.h
@@ -47,4 +47,5 @@ private:
     MSG                    m_event;
     UINT                m_daemonQuit;
     IEventQueue*        m_events;
+    UINT                m_os_supported_message_types;
 };