From 9923a901008654794a84f357a69e60b77cc86aef Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?M=C3=A5rten=20Nordheim?= <marten.nordheim@qt.io>
Date: Wed, 7 Apr 2021 14:27:21 +0200
Subject: [PATCH] QtFuture::connect: disconnect signals first

During reportFinished we may call a continuation which might end up
triggering one of the signals.

Change-Id: I19546fcca12be71cd536e4287eb5eddd9d236830
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit bb85831e4de5e2c4951a0c40003ccf36f57cbd93)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/thread/qfuture_impl.h             | 14 +++++++-------
 .../corelib/thread/qfuture/tst_qfuture.cpp    | 19 +++++++++++++++++++
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/src/corelib/thread/qfuture_impl.h b/src/corelib/thread/qfuture_impl.h
index 8e7ba0c4b59..e455a74793d 100644
--- a/src/corelib/thread/qfuture_impl.h
+++ b/src/corelib/thread/qfuture_impl.h
@@ -807,34 +807,34 @@ static QFuture<ArgsType<Signal>> connect(Sender *sender, Signal signal)
     if constexpr (std::is_void_v<ArgsType>) {
         connections->first =
                 QObject::connect(sender, signal, sender, [promise, connections]() mutable {
-                    promise.reportFinished();
                     QObject::disconnect(connections->first);
                     QObject::disconnect(connections->second);
+                    promise.reportFinished();
                 });
     } else if constexpr (QtPrivate::isTupleV<ArgsType>) {
         connections->first = QObject::connect(sender, signal, sender,
                                               [promise, connections](auto... values) mutable {
-                                                  promise.reportResult(std::make_tuple(values...));
-                                                  promise.reportFinished();
                                                   QObject::disconnect(connections->first);
                                                   QObject::disconnect(connections->second);
+                                                  promise.reportResult(std::make_tuple(values...));
+                                                  promise.reportFinished();
                                               });
     } else {
         connections->first = QObject::connect(sender, signal, sender,
                                               [promise, connections](ArgsType value) mutable {
-                                                  promise.reportResult(value);
-                                                  promise.reportFinished();
                                                   QObject::disconnect(connections->first);
                                                   QObject::disconnect(connections->second);
+                                                  promise.reportResult(value);
+                                                  promise.reportFinished();
                                               });
     }
 
     connections->second =
             QObject::connect(sender, &QObject::destroyed, sender, [promise, connections]() mutable {
-                promise.reportCanceled();
-                promise.reportFinished();
                 QObject::disconnect(connections->first);
                 QObject::disconnect(connections->second);
+                promise.reportCanceled();
+                promise.reportFinished();
             });
 
     return promise.future();
diff --git a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
index 71cfbd054b7..5f6267ec7d6 100644
--- a/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
+++ b/tests/auto/corelib/thread/qfuture/tst_qfuture.cpp
@@ -3228,6 +3228,25 @@ void tst_QFuture::signalConnect()
         QVERIFY(future.isCanceled());
         QVERIFY(!future.isValid());
     }
+
+    // Signal emitted, causing Sender to be destroyed
+    {
+        SenderObject *sender = new SenderObject();
+
+        auto future = QtFuture::connect(sender, &SenderObject::intArgSignal);
+        future.then([sender](int) {
+            // Scenario: Sender no longer needed, so it's deleted
+            delete sender;
+        });
+
+        QSignalSpy spy(sender, &SenderObject::destroyed);
+        emit sender->intArgSignal(5);
+        spy.wait();
+
+        QVERIFY(future.isFinished());
+        QVERIFY(!future.isCanceled());
+        QVERIFY(future.isValid());
+    }
 }
 
 void tst_QFuture::waitForFinished()