Fix problem with exception reporting in QFuture::waitForResult()

This fixes a problem that occurs when a task, that is run synchronously,
throws an exception. If that happened, then the exception would not be
re-thrown, because of an early return.

Task-number: QTBUG-54831
Change-Id: Ic70c5b810ec6adce6e62bfd6832ba9f170b13a7f
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@theqtcompany.com>

2 files changed, 42 insertions, 6 deletions

diff --git a/src/corelib/thread/qfutureinterface.cpp b/src/corelib/thread/qfutureinterface.cpp
index 60155c96fd..2fe038165b 100644
--- a/src/corelib/thread/qfutureinterface.cpp
+++ b/src/corelib/thread/qfutureinterface.cpp
@@ -299,12 +299,11 @@ void QFutureInterfaceBase::waitForResult(int resultIndex)
 
     lock.relock();
 
-    if (!(d->state & Running))
-        return;
-
-    const int waitIndex = (resultIndex == -1) ? INT_MAX : resultIndex;
-    while ((d->state & Running) && d->internal_isResultReadyAt(waitIndex) == false)
-        d->waitCondition.wait(&d->m_mutex);
+    if (d->state & Running) {
+        const int waitIndex = (resultIndex == -1) ? INT_MAX : resultIndex;
+        while ((d->state & Running) && d->internal_isResultReadyAt(waitIndex) == false)
+            d->waitCondition.wait(&d->m_mutex);
+    }
 
     d->m_exceptionStore.throwPossibleException();
 }
diff --git a/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp b/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
index 8ffe4d8dfe..7e057f3bcf 100644
--- a/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
+++ b/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
@@ -440,6 +440,19 @@ int throwFunctionReturn()
     return 0;
 }
 
+class SlowTask : public QRunnable
+{
+public:
+    static QAtomicInt cancel;
+    void run() Q_DECL_OVERRIDE {
+        int iter = 60;
+        while (--iter && !cancel.load())
+            QThread::currentThread()->msleep(25);
+    }
+};
+
+QAtomicInt SlowTask::cancel;
+
 void tst_QtConcurrentRun::exceptions()
 {
     QThreadPool pool;
@@ -480,6 +493,30 @@ void tst_QtConcurrentRun::exceptions()
     }
     if (!caught)
         QFAIL("did not get exception");
+
+    caught = false;
+    try  {
+        QtConcurrent::run(&pool, throwFunctionReturn).result();
+    } catch (QException &) {
+        caught = true;
+    }
+    QVERIFY2(caught, "did not get exception");
+
+    // Force the task to be run on this thread.
+    caught = false;
+    QThreadPool shortPool;
+    shortPool.setMaxThreadCount(1);
+    SlowTask *st = new SlowTask();
+    try  {
+        shortPool.start(st);
+        QtConcurrent::run(&shortPool, throwFunctionReturn).result();
+    } catch (QException &) {
+        caught = true;
+    }
+
+    SlowTask::cancel.store(true);
+
+    QVERIFY2(caught, "did not get exception");
 }
 #endif