Disable spinning under lock contention on single CPU machines

Spinning is just wasted time on these systems.

Reviewed-by: joao

1 files changed, 10 insertions, 0 deletions

diff --git a/src/corelib/thread/qmutex.cpp b/src/corelib/thread/qmutex.cpp
index 19e2457..54b3ed4 100644
--- a/src/corelib/thread/qmutex.cpp
+++ b/src/corelib/thread/qmutex.cpp
@@ -429,6 +429,16 @@ void QMutex::unlock()
 void QMutex::lockInternal()
 {
     QMutexPrivate *d = static_cast<QMutexPrivate *>(this->d);
+
+    if (QThread::idealThreadCount() == 1) {
+        // don't spin on single cpu machines
+        bool isLocked = d->wait();
+        Q_ASSERT_X(isLocked, "QMutex::lock",
+                   "Internal error, infinite wait has timed out.");
+        Q_UNUSED(isLocked);
+        return;
+    }
+
     int spinCount = 0;
     int lastSpinCount = d->lastSpinCount;