QtConcurrent::run: support non default-constructible return types

The QtConcurrent::RunFunctionTask class keeps a variable to store the
result of QtConcurrent::run when it becomes available, so that it can be
reported afterwards. This requires the result type to be
default-constructible. However there's no need in storing the result, it
can be reported immediately after it becomes available.

Pick-to: 6.1 6.2
Fixes: QTBUG-95214
Change-Id: I95f3dbff0ab41eaa81b104a8834b37d10a0d193a
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>
Reviewed-by: Andrei Golubev <andrei.golubev@qt.io>

2 files changed, 16 insertions, 4 deletions

diff --git a/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp b/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
index 1b0b9577cf..235ffca0fc 100644
--- a/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
+++ b/tests/auto/concurrent/qtconcurrentrun/tst_qtconcurrentrun.cpp
@@ -64,6 +64,7 @@ private slots:
     void moveOnlyType();
     void crefFunction();
     void customPromise();
+    void nonDefaultConstructibleValue();
 };
 
 void light()
@@ -1564,6 +1565,17 @@ void tst_QtConcurrentRun::customPromise()
     QCOMPARE(p.future().progressMaximum(), 10);
 }
 
+void tst_QtConcurrentRun::nonDefaultConstructibleValue()
+{
+    struct NonDefaultConstructible
+    {
+        explicit NonDefaultConstructible(int v) : value(v) { }
+        int value = 0;
+    };
+
+    auto future = QtConcurrent::run([] { return NonDefaultConstructible(42); });
+    QCOMPARE(future.result().value, 42);
+}
 
 QTEST_MAIN(tst_QtConcurrentRun)
 #include "tst_qtconcurrentrun.moc"
diff --git a/tests/auto/corelib/thread/qfuturewatcher/tst_qfuturewatcher.cpp b/tests/auto/corelib/thread/qfuturewatcher/tst_qfuturewatcher.cpp
index 929047c07e..33ecfb9cab 100644
--- a/tests/auto/corelib/thread/qfuturewatcher/tst_qfuturewatcher.cpp
+++ b/tests/auto/corelib/thread/qfuturewatcher/tst_qfuturewatcher.cpp
@@ -229,12 +229,12 @@ void tst_QFutureWatcher::canceled()
     future.waitForFinished();
 }
 
-class IntTask : public RunFunctionTask<int>
+class IntTask : public RunFunctionTaskBase<int>
 {
 public:
     void runFunctor() override
     {
-        result = 10;
+        promise.reportResult(10);
     }
 };
 
@@ -463,7 +463,7 @@ void tst_QFutureWatcher::disconnectRunningFuture()
 }
 
 const int maxProgress = 100000;
-class ProgressEmitterTask : public RunFunctionTask<void>
+class ProgressEmitterTask : public RunFunctionTaskBase<void>
 {
 public:
     void runFunctor() override
@@ -493,7 +493,7 @@ void tst_QFutureWatcher::tooMuchProgress()
 }
 
 template <typename T>
-class ProgressTextTask : public RunFunctionTask<T>
+class ProgressTextTask : public RunFunctionTaskBase<T>
 {
 public:
     void runFunctor() override