Fix race condition between QEventLoop::exec and QThread::exit

As also mentioned in QTBUG-16692

Reviewed-by: brad
Task-number: QTBUG-17257

4 files changed, 29 insertions, 2 deletions

diff --git a/src/corelib/kernel/qeventloop.cpp b/src/corelib/kernel/qeventloop.cpp
index e78f86a..d213b0e 100644
--- a/src/corelib/kernel/qeventloop.cpp
+++ b/src/corelib/kernel/qeventloop.cpp
@@ -175,6 +175,8 @@ bool QEventLoop::processEvents(ProcessEventsFlags flags)
 int QEventLoop::exec(ProcessEventsFlags flags)
 {
     Q_D(QEventLoop);
+    //we need to protect from race condition with QThread::exit
+    QMutexLocker locker(&static_cast<QThreadPrivate *>(QObjectPrivate::get(d->threadData->thread))->mutex);
     if (d->threadData->quitNow)
         return -1;
 
@@ -186,6 +188,7 @@ int QEventLoop::exec(ProcessEventsFlags flags)
     d->exit = false;
     ++d->threadData->loopLevel;
     d->threadData->eventLoops.push(this);
+    locker.unlock();
 
     // remove posted quit events when entering a new event loop
     QCoreApplication *app = QCoreApplication::instance();
@@ -205,6 +208,7 @@ int QEventLoop::exec(ProcessEventsFlags flags)
                  "reimplement QApplication::notify() and catch all exceptions there.\n");
 
         // copied from below
+        locker.relock();
         QEventLoop *eventLoop = d->threadData->eventLoops.pop();
         Q_ASSERT_X(eventLoop == this, "QEventLoop::exec()", "internal error");
         Q_UNUSED(eventLoop); // --release warning
@@ -216,6 +220,7 @@ int QEventLoop::exec(ProcessEventsFlags flags)
 #endif
 
     // copied above
+    locker.relock();
     QEventLoop *eventLoop = d->threadData->eventLoops.pop();
     Q_ASSERT_X(eventLoop == this, "QEventLoop::exec()", "internal error");
     Q_UNUSED(eventLoop); // --release warning
diff --git a/src/corelib/thread/qthread_unix.cpp b/src/corelib/thread/qthread_unix.cpp
index 891ac77..5e0d2a2 100644
--- a/src/corelib/thread/qthread_unix.cpp
+++ b/src/corelib/thread/qthread_unix.cpp
@@ -327,7 +327,10 @@ void *QThreadPrivate::start(void *arg)
     set_thread_data(data);
 
     data->ref();
-    data->quitNow = false;
+    {
+        QMutexLocker locker(&thr->d_func()->mutex);
+        data->quitNow = thr->d_func()->exited;
+    }
 
     // ### TODO: allow the user to create a custom event dispatcher
     createEventDispatcher(data);
diff --git a/src/corelib/thread/qthread_win.cpp b/src/corelib/thread/qthread_win.cpp
index cb2d1a9..f2d1310 100644
--- a/src/corelib/thread/qthread_win.cpp
+++ b/src/corelib/thread/qthread_win.cpp
@@ -298,7 +298,10 @@ unsigned int __stdcall QThreadPrivate::start(void *arg)
 
     QThread::setTerminationEnabled(false);
 
-    data->quitNow = false;
+    {
+        QMutexLocker locker(&thr->d_func()->mutex);
+        data->quitNow = !thr->d_func()->exited;
+    }
     // ### TODO: allow the user to create a custom event dispatcher
     createEventDispatcher(data);
 
diff --git a/tests/auto/qthread/tst_qthread.cpp b/tests/auto/qthread/tst_qthread.cpp
index 19c6c16..c69052e 100644
--- a/tests/auto/qthread/tst_qthread.cpp
+++ b/tests/auto/qthread/tst_qthread.cpp
@@ -113,6 +113,7 @@ private slots:
     void wait3_slowDestructor();
     void destroyFinishRace();
     void startFinishRace();
+    void startAndQuitCustomEventLoop();
 
     void stressTest();
 };
@@ -1150,5 +1151,20 @@ void tst_QThread::startFinishRace()
     }
 }
 
+void tst_QThread::startAndQuitCustomEventLoop()
+{
+    struct Thread : QThread {
+        void run() { QEventLoop().exec(); }
+    };
+
+   for (int i = 0; i < 5; i++) {
+       Thread t;
+       t.start();
+       t.quit();
+       t.wait();
+   }
+}
+
+
 QTEST_MAIN(tst_QThread)
 #include "tst_qthread.moc"