2 files changed, 47 insertions, 22 deletions

diff --git a/src/corelib/thread/qfuture_impl.h b/src/corelib/thread/qfuture_impl.h
index 5b4c929a36..d8fe946b92 100644
--- a/src/corelib/thread/qfuture_impl.h
+++ b/src/corelib/thread/qfuture_impl.h
@@ -590,6 +590,18 @@ void Continuation<Function, ResultType, ParentResultType>::create(F &&func,
     f->d.setContinuation(ContinuationWrapper(std::move(continuation)), fi.d);
 }
 
+// defined in qfutureinterface.cpp:
+Q_CORE_EXPORT void watchContinuationImpl(const QObject *context, QSlotObjectBase *slotObj,
+                                         QFutureInterfaceBase &fi);
+template <typename Continuation>
+void watchContinuation(const QObject *context, Continuation &&c, QFutureInterfaceBase &fi)
+{
+    using Prototype = typename QtPrivate::Callable<Continuation>::Function;
+    watchContinuationImpl(context,
+                          QtPrivate::makeCallableObject<Prototype>(std::forward<Continuation>(c)),
+                          fi);
+}
+
 template<typename Function, typename ResultType, typename ParentResultType>
 template<typename F>
 void Continuation<Function, ResultType, ParentResultType>::create(F &&func,
@@ -610,15 +622,7 @@ void Continuation<Function, ResultType, ParentResultType>::create(F &&func,
         continuationJob.execute();
     };
 
-    auto *watcher = new QBasicFutureWatcher;
-    watcher->moveToThread(context->thread());
-    QObject::connect(watcher, &QBasicFutureWatcher::finished,
-                     context, std::move(continuation));
-    QObject::connect(watcher, &QBasicFutureWatcher::finished,
-                     watcher, &QObject::deleteLater);
-    QObject::connect(context, &QObject::destroyed,
-                     watcher, &QObject::deleteLater);
-    watcher->setFuture(f->d);
+    QtPrivate::watchContinuation(context, std::move(continuation), f->d);
 }
 
 template<typename Function, typename ResultType, typename ParentResultType>
@@ -710,12 +714,7 @@ void FailureHandler<Function, ResultType>::create(F &&function, QFuture<ResultTy
         failureHandler.run();
     };
 
-    auto *watcher = new QBasicFutureWatcher;
-    watcher->moveToThread(context->thread());
-    QObject::connect(watcher, &QBasicFutureWatcher::finished, context, std::move(failureContinuation));
-    QObject::connect(watcher, &QBasicFutureWatcher::finished, watcher, &QObject::deleteLater);
-    QObject::connect(context, &QObject::destroyed, watcher, &QObject::deleteLater);
-    watcher->setFuture(future->d);
+    QtPrivate::watchContinuation(context, std::move(failureContinuation), future->d);
 }
 
 template<class Function, class ResultType>
@@ -809,13 +808,7 @@ public:
             run(std::forward<F>(handler), parentFuture, std::move(promise));
         };
 
-        auto *watcher = new QBasicFutureWatcher;
-        watcher->moveToThread(context->thread());
-        QObject::connect(watcher, &QBasicFutureWatcher::finished,
-                         context, std::move(canceledContinuation));
-        QObject::connect(watcher, &QBasicFutureWatcher::finished, watcher, &QObject::deleteLater);
-        QObject::connect(context, &QObject::destroyed, watcher, &QObject::deleteLater);
-        watcher->setFuture(future->d);
+        QtPrivate::watchContinuation(context, std::move(canceledContinuation), future->d);
     }
 
     template<class F = Function>
diff --git a/src/corelib/thread/qfutureinterface.cpp b/src/corelib/thread/qfutureinterface.cpp
index 8f73dde253..de936005c3 100644
--- a/src/corelib/thread/qfutureinterface.cpp
+++ b/src/corelib/thread/qfutureinterface.cpp
@@ -4,12 +4,14 @@
 // qfutureinterface.h included from qfuture.h
 #include "qfuture.h"
 #include "qfutureinterface_p.h"
+#include "qbasicfuturewatcher.h"
 
 #include <QtCore/qatomic.h>
 #include <QtCore/qthread.h>
 #include <QtCore/qvarlengtharray.h>
 #include <QtCore/private/qsimd_p.h> // for qYieldCpu()
 #include <private/qthreadpool_p.h>
+#include <private/qobject_p.h>
 
 #ifdef interface
 #  undef interface
@@ -43,6 +45,36 @@ const auto suspendingOrSuspended =
 
 } // unnamed namespace
 
+void QtPrivate::watchContinuationImpl(const QObject *context, QSlotObjectBase *slotObj,
+                                      QFutureInterfaceBase &fi)
+{
+    Q_ASSERT(context);
+    Q_ASSERT(slotObj);
+
+    // ### we're missing `QSlotObjectPtr`...
+    struct Deleter {
+        void operator()(QSlotObjectBase *p) const { p->destroyIfLastRef(); }
+    };
+    auto slot = std::unique_ptr<QSlotObjectBase, Deleter>(slotObj);
+
+    auto *watcher = new QBasicFutureWatcher;
+    watcher->moveToThread(context->thread());
+    // ### we're missing a convenient way to `QObject::connect()` to a `QSlotObjectBase`...
+    QObject::connect(watcher, &QBasicFutureWatcher::finished,
+                     // for the following, cf. QMetaObject::invokeMethodImpl():
+                     // we know `slot` is a lambda returning `void`, so we can just
+                     // `call()` with `obj` and `args[0]` set to `nullptr`:
+                     watcher, [slot = std::move(slot)] {
+                         void *args[] = { nullptr }; // for `void` return value
+                         slot->call(nullptr, args);
+                     });
+    QObject::connect(watcher, &QBasicFutureWatcher::finished,
+                     watcher, &QObject::deleteLater);
+    QObject::connect(context, &QObject::destroyed,
+                     watcher, &QObject::deleteLater);
+    watcher->setFuture(fi);
+}
+
 QFutureCallOutInterface::~QFutureCallOutInterface()
     = default;