QFutureWatcher: display a warning when connecting after calling setFuture()

Reviewed-by: brad

2 files changed, 32 insertions, 1 deletions

diff --git a/src/corelib/concurrent/qfuturewatcher.cpp b/src/corelib/concurrent/qfuturewatcher.cpp
index d4573c6..21b0789 100644
--- a/src/corelib/concurrent/qfuturewatcher.cpp
+++ b/src/corelib/concurrent/qfuturewatcher.cpp
@@ -359,6 +359,15 @@ void QFutureWatcherBase::connectNotify(const char * signal)
     Q_D(QFutureWatcherBase);
     if (qstrcmp(signal, SIGNAL(resultReadyAt(int))) == 0)
         d->resultAtConnected.ref();
+#ifndef QT_NO_DEBUG
+    if (qstrcmp(signal, SIGNAL(finished())) == 0) {
+        if (futureInterface().isRunning()) {
+            //connections should be established before calling stFuture to avoid race.
+            // (The future could finish before the connection is made.)
+            qWarning("QFutureWatcher::connect: connecting after calling setFuture() is likely to produce race");
+        }
+    }
+#endif
 }
 
 void QFutureWatcherBase::disconnectNotify(const char * signal)
diff --git a/tests/auto/qfuturewatcher/tst_qfuturewatcher.cpp b/tests/auto/qfuturewatcher/tst_qfuturewatcher.cpp
index c53c67a..8b52761 100644
--- a/tests/auto/qfuturewatcher/tst_qfuturewatcher.cpp
+++ b/tests/auto/qfuturewatcher/tst_qfuturewatcher.cpp
@@ -81,6 +81,7 @@ private slots:
     void incrementalMapResults();
     void incrementalFilterResults();
     void qfutureSynchornizer();
+    void warnRace();
 };
 
 QTEST_MAIN(tst_QFutureWatcher)
@@ -466,12 +467,12 @@ void tst_QFutureWatcher::toMuchProgress()
     ProgressObject o;
 
     QFutureWatcher<void> f;
-    f.setFuture((new ProgressEmitterTask())->start());
     QObject::connect(&f, SIGNAL(finished()), &QTestEventLoop::instance(), SLOT(exitLoop()));
 #ifdef PRINT
     QObject::connect(&f, SIGNAL(progressValueChanged(int)), &o, SLOT(printProgress(int)));
 #endif
     QObject::connect(&f, SIGNAL(progressValueChanged(int)), &o, SLOT(registerProgress(int)));
+    f.setFuture((new ProgressEmitterTask())->start());
 
     QTestEventLoop::instance().enterLoop(5);
     QVERIFY(!QTestEventLoop::instance().timeout());
@@ -886,6 +887,27 @@ void tst_QFutureWatcher::qfutureSynchornizer()
     QVERIFY(t.elapsed() < taskCount * 10);
 }
 
+class DummyObject : public QObject {
+    Q_OBJECT
+public slots:
+    void dummySlot() {}
+};
+
+void tst_QFutureWatcher::warnRace()
+{
+#ifndef QT_NO_DEBUG
+    QTest::ignoreMessage(QtWarningMsg, "QFutureWatcher::connect: connecting after calling setFuture() is likely to produce race");
+#endif
+    QFutureWatcher<void> watcher;
+    DummyObject object;
+
+    QFuture<void> future = QtConcurrent::run(sleeper);
+    watcher.setFuture(future);
+    connect(&watcher, SIGNAL(finished()), &object, SLOT(dummySlot()));
+    future.waitForFinished();
+}
+
+
 #include "tst_qfuturewatcher.moc"
 
 #else