QPromise: Propagate cancellation through failure handlers

Previously, failure handlers did not propagate cancellation. This would
lead to crashes when a QPromise was cancelled without having generated
any result. Subsequent continuations would be invoked and try to access
the result (which was nonexistent) and then crash.
This patch propagates cancellation through failure handlers to prevent
subsequent continuations from being called in the first place.

Fixes: QTBUG-114606
Pick-to: 6.6
Pick-to: 6.5
Change-Id: I23b28a8e70a76e1ba6416be4440360c6dbaef2a3
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>

1 files changed, 2 insertions, 0 deletions

diff --git a/src/corelib/thread/qfuture_impl.h b/src/corelib/thread/qfuture_impl.h
index 53f2326cde..5b4c929a36 100644
--- a/src/corelib/thread/qfuture_impl.h
+++ b/src/corelib/thread/qfuture_impl.h
@@ -732,6 +732,8 @@ void FailureHandler<Function, ResultType>::run()
         } else {
             handleException<ArgType>();
         }
+    } else if (parentFuture.d.isChainCanceled()) {
+        promise.future().cancel();
     } else {
         QtPrivate::fulfillPromise(promise, parentFuture);
     }