QMutex: de-inline lock(), unlock(), and tryLock()

See the discussion of this topic on the mailing list:
http://lists.qt-project.org/pipermail/development/2012-May/003943.html

The consensus is to not have these methods have inline code to actually
acquire the lock (i.e. no atomic test-and-set or similar). QBasicMutex
is unchanged, and continues to have inlined lock(), tryLock(), and
unlock(). QMutexLocker has been changed to always call QMutex::lock()
(even though the constructor takes a QBasicMutex parameter).

Change-Id: Ic7d2d9d581e6b254c84fdfdd8ce6c425535a8078
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 23 insertions, 7 deletions

diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp
index 145916d750..d310f56798 100644
--- a/src/corelib/thread/qmutex.cpp
+++ b/src/corelib/thread/qmutex.cpp
@@ -177,6 +177,10 @@ QMutex::~QMutex()
 
     \sa unlock()
 */
+void QMutex::lock()
+{
+    QBasicMutex::lock();
+}
 
 /*! \fn bool QMutex::tryLock(int timeout)
 
@@ -201,7 +205,10 @@ QMutex::~QMutex()
 
     \sa lock(), unlock()
 */
-
+bool QMutex::tryLock(int timeout)
+{
+    return QBasicMutex::tryLock(timeout);
+}
 
 /*! \fn void QMutex::unlock()
     Unlocks the mutex. Attempting to unlock a mutex in a different
@@ -210,6 +217,10 @@ QMutex::~QMutex()
 
     \sa lock()
 */
+void QMutex::unlock()
+{
+    QBasicMutex::unlock();
+}
 
 /*!
     \fn void QMutex::isRecursive()
diff --git a/src/corelib/thread/qmutex.h b/src/corelib/thread/qmutex.h
index 0743c36457..22da73a8b8 100644
--- a/src/corelib/thread/qmutex.h
+++ b/src/corelib/thread/qmutex.h
@@ -96,8 +96,16 @@ public:
     enum RecursionMode { NonRecursive, Recursive };
     explicit QMutex(RecursionMode mode = NonRecursive);
     ~QMutex();
+
+    void lock();
+    bool tryLock(int timeout = 0);
+    void unlock();
+
+    using QBasicMutex::isRecursive;
+
 private:
     Q_DISABLE_COPY(QMutex)
+    friend class QMutexLocker;
 };
 
 class Q_CORE_EXPORT QMutexLocker
@@ -107,12 +115,9 @@ public:
     {
         Q_ASSERT_X((reinterpret_cast<quintptr>(m) & quintptr(1u)) == quintptr(0),
                    "QMutexLocker", "QMutex pointer is misaligned");
-        if (m) {
-            m->lock();
-            val = reinterpret_cast<quintptr>(m) | quintptr(1u);
-        } else {
-            val = 0;
-        }
+        val = quintptr(m);
+        // relock() here ensures that we call QMutex::lock() instead of QBasicMutex::lock()
+        relock();
     }
     inline ~QMutexLocker() { unlock(); }