From c6d1e7ad389a6db61a33016347772f885bf5e7d9 Mon Sep 17 00:00:00 2001
From: Alex Trotsenko <alex1973tr@gmail.com>
Date: Thu, 17 Sep 2020 16:41:45 +0300
Subject: [PATCH] QWinEventNotifier: reinterpret 'int signaledCount' as a 'bool
 signaled'

In fact, this variable can take only two values: 0 and 1. By
interpreting its value as boolean, we can use relaxed store operations
instead of atomic increments. This is safe, because it's guarded by
'activateEventNotifiersPosted' variable, which already provides a
release/acquire semantic.

Change-Id: If9adb7d022f1500ee7e8b61f336d8732f9b88d4c
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>
---
 src/corelib/kernel/qeventdispatcher_win.cpp | 4 ++--
 src/corelib/kernel/qwineventnotifier.cpp    | 4 ++--
 src/corelib/kernel/qwineventnotifier_p.h    | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/corelib/kernel/qeventdispatcher_win.cpp b/src/corelib/kernel/qeventdispatcher_win.cpp
index 792260fb984..9cf426dd73c 100644
--- a/src/corelib/kernel/qeventdispatcher_win.cpp
+++ b/src/corelib/kernel/qeventdispatcher_win.cpp
@@ -877,8 +877,8 @@ void QEventDispatcherWin32::activateEventNotifiers()
         for (int i = 0; i < d->winEventNotifierList.count(); ++i) {
             QWinEventNotifier *notifier = d->winEventNotifierList.at(i);
             QWinEventNotifierPrivate *nd = QWinEventNotifierPrivate::get(notifier);
-            if (nd->signaledCount.loadRelaxed() != 0) {
-                --nd->signaledCount;
+            if (nd->signaled.loadRelaxed()) {
+                nd->signaled.storeRelaxed(false);
                 nd->unregisterWaitObject();
                 d->activateEventNotifier(notifier);
             }
diff --git a/src/corelib/kernel/qwineventnotifier.cpp b/src/corelib/kernel/qwineventnotifier.cpp
index 8cf6b018d48..5a3ad9ed5d5 100644
--- a/src/corelib/kernel/qwineventnotifier.cpp
+++ b/src/corelib/kernel/qwineventnotifier.cpp
@@ -202,7 +202,7 @@ void QWinEventNotifier::setEnabled(bool enable)
     }
 
     if (enable) {
-        d->signaledCount = 0;
+        d->signaled.storeRelaxed(false);
         eventDispatcher->registerEventNotifier(this);
     } else {
         eventDispatcher->unregisterEventNotifier(this);
@@ -245,7 +245,7 @@ static void CALLBACK wfsoCallback(void *context, BOOLEAN /*ignore*/)
 
     QEventDispatcherWin32Private *edp = QEventDispatcherWin32Private::get(
                 static_cast<QEventDispatcherWin32 *>(eventDispatcher));
-    ++nd->signaledCount;
+    nd->signaled.storeRelaxed(true);
     edp->postActivateEventNotifiers();
 }
 
diff --git a/src/corelib/kernel/qwineventnotifier_p.h b/src/corelib/kernel/qwineventnotifier_p.h
index 8bb2c3159a2..f8f7cd8effe 100644
--- a/src/corelib/kernel/qwineventnotifier_p.h
+++ b/src/corelib/kernel/qwineventnotifier_p.h
@@ -74,7 +74,7 @@ public:
 
     HANDLE handleToEvent;
     HANDLE waitHandle = NULL;
-    QAtomicInt signaledCount;
+    QAtomicInt signaled;
     bool enabled;
 };