From d84da399649d01ac689e87295f8decc024a4f8e8 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Thu, 16 Aug 2012 17:15:33 +0200
Subject: Use the new 3-operand testAndSet functions in QMutex

This allows us to get the current value of the QMutex / QBasicMutex
after the testAndSet operation failed. It saves an extra load from
memory.

Change-Id: I4922a8b3df15e342b177b13f56cf4f1184314520
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
---
 src/corelib/thread/qmutex.cpp | 12 ++++++------
 src/corelib/thread/qmutex.h   |  6 ++++++
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp
index 0f305b79af..fe5beb1c01 100644
--- a/src/corelib/thread/qmutex.cpp
+++ b/src/corelib/thread/qmutex.cpp
@@ -216,9 +216,9 @@ QMutex::~QMutex()
 */
 void QMutex::lock() QT_MUTEX_LOCK_NOEXCEPT
 {
-    if (fastTryLock())
+    QMutexData *current;
+    if (fastTryLock(current))
         return;
-    QMutexData *current = d_ptr.loadAcquire();
     if (QT_PREPEND_NAMESPACE(isRecursive)(current))
         static_cast<QRecursiveMutexPrivate *>(current)->lock(-1);
     else
@@ -250,9 +250,9 @@ void QMutex::lock() QT_MUTEX_LOCK_NOEXCEPT
 */
 bool QMutex::tryLock(int timeout) QT_MUTEX_LOCK_NOEXCEPT
 {
-    if (fastTryLock())
+    QMutexData *current;
+    if (fastTryLock(current))
         return true;
-    QMutexData *current = d_ptr.loadAcquire();
     if (QT_PREPEND_NAMESPACE(isRecursive)(current))
         return static_cast<QRecursiveMutexPrivate *>(current)->lock(timeout);
     else
@@ -268,9 +268,9 @@ bool QMutex::tryLock(int timeout) QT_MUTEX_LOCK_NOEXCEPT
 */
 void QMutex::unlock() Q_DECL_NOTHROW
 {
-    if (fastTryUnlock())
+    QMutexData *current;
+    if (fastTryUnlock(current))
         return;
-    QMutexData *current = d_ptr.loadAcquire();
     if (QT_PREPEND_NAMESPACE(isRecursive)(current))
         static_cast<QRecursiveMutexPrivate *>(current)->unlock();
     else
diff --git a/src/corelib/thread/qmutex.h b/src/corelib/thread/qmutex.h
index 0bca0def22..0ecc96a9b1 100644
--- a/src/corelib/thread/qmutex.h
+++ b/src/corelib/thread/qmutex.h
@@ -86,6 +86,12 @@ private:
     inline bool fastTryUnlock() Q_DECL_NOTHROW {
         return d_ptr.testAndSetRelease(dummyLocked(), 0);
     }
+    inline bool fastTryLock(QMutexData *&current) Q_DECL_NOTHROW {
+        return d_ptr.testAndSetAcquire(0, dummyLocked(), current);
+    }
+    inline bool fastTryUnlock(QMutexData *&current) Q_DECL_NOTHROW {
+        return d_ptr.testAndSetRelease(dummyLocked(), 0, current);
+    }
 
     void lockInternal() QT_MUTEX_LOCK_NOEXCEPT;
     bool lockInternal(int timeout) QT_MUTEX_LOCK_NOEXCEPT;
-- 
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