From 917214c4992604bac494e82e56a2bed0c42892fc Mon Sep 17 00:00:00 2001
From: Mat Sutcliffe <oktal3700@gmail.com>
Date: Sat, 27 Oct 2018 22:31:09 +0100
Subject: [PATCH] Ref T414 Use a promise/future pair in CWorker::thenWithResult
 to avoid accessing the worker after it was potentially destroyed.

---
 src/blackmisc/worker.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/blackmisc/worker.h b/src/blackmisc/worker.h
index b0cf820b9..3d9c31c64 100644
--- a/src/blackmisc/worker.h
+++ b/src/blackmisc/worker.h
@@ -37,6 +37,7 @@
 #include <memory>
 #include <type_traits>
 #include <atomic>
+#include <future>
 
 namespace BlackMisc
 {
@@ -244,7 +245,14 @@ namespace BlackMisc
         void thenWithResult(T *context, F functor)
         {
             Q_ASSERT_X(m_result.canConvert<R>(), Q_FUNC_INFO, "Type in thenWithResult must match return type of task");
-            then(context, [this, context, functor]() { Private::invokeSlot(functor, context, this->resultNoWait<R>()); });
+
+            // MS 2018-10 It is possible that a queued finished() signal will be delivered after the worker was
+            //            destroyed, so we can't refer to the this pointer inside the contextual then() lambda.
+            //            Therefore we use a promise to extract the result from a non-contextual then(). See T414.
+            auto promise = std::make_shared<std::promise<R>>();
+            auto future = promise->get_future().share();
+            then([this, promise]() { promise->set_value(this->resultNoWait<R>()); });
+            then(context, [context, functor, future]() { Private::invokeSlot(functor, context, future.get()); });
         }
 
         //! Returns the result of the task, waiting for it to finish if necessary.