1 files changed, 148 insertions, 57 deletions

diff --git a/src/corelib/thread/qfutureinterface.cpp b/src/corelib/thread/qfutureinterface.cpp
index a82b7af873..f83306af00 100644
--- a/src/corelib/thread/qfutureinterface.cpp
+++ b/src/corelib/thread/qfutureinterface.cpp
@@ -6,13 +6,11 @@
 #include "qfutureinterface_p.h"
 
 #include <QtCore/qatomic.h>
+#include <QtCore/qcoreapplication.h>
 #include <QtCore/qthread.h>
-#include <QtCore/private/qsimd_p.h> // for qYieldCpu()
+#include <QtCore/qvarlengtharray.h>
 #include <private/qthreadpool_p.h>
-
-#ifdef interface
-#  undef interface
-#endif
+#include <private/qobject_p.h>
 
 // GCC 12 gets confused about QFutureInterfaceBase::state, for some non-obvious
 // reason
@@ -29,6 +27,7 @@ namespace {
 class ThreadPoolThreadReleaser {
     QThreadPool *m_pool;
 public:
+    Q_NODISCARD_CTOR
     explicit ThreadPoolThreadReleaser(QThreadPool *pool)
         : m_pool(pool)
     { if (pool) pool->releaseThread(); }
@@ -41,6 +40,63 @@ const auto suspendingOrSuspended =
 
 } // unnamed namespace
 
+class QObjectContinuationWrapper : public QObject
+{
+    Q_OBJECT
+public:
+    explicit QObjectContinuationWrapper(QObject *parent = nullptr)
+        : QObject(parent)
+    {
+    }
+
+signals:
+    void run();
+};
+
+void QtPrivate::watchContinuationImpl(const QObject *context, QSlotObjectBase *slotObj,
+                                      QFutureInterfaceBase &fi)
+{
+    Q_ASSERT(context);
+    Q_ASSERT(slotObj);
+
+    auto slot = SlotObjUniquePtr(slotObj);
+
+    auto *watcher = new QObjectContinuationWrapper;
+    watcher->moveToThread(context->thread());
+
+    // We need to protect acccess to the watcher. The context object (and in turn, the watcher)
+    // could be destroyed while the continuation that emits the signal is running. We have to
+    // prevent that.
+    // The mutex has to be recursive, because the continuation itself could delete the context
+    // object (and thus the watcher), which will try to lock the mutex from the same thread twice.
+    auto watcherMutex = std::make_shared<QRecursiveMutex>();
+    const auto destroyWatcher = [watcherMutex, watcher]() mutable {
+        QMutexLocker lock(watcherMutex.get());
+        delete watcher;
+    };
+
+    // ### we're missing a convenient way to `QObject::connect()` to a `QSlotObjectBase`...
+    QObject::connect(watcher, &QObjectContinuationWrapper::run,
+                     // 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`:
+                     context, [slot = std::move(slot)] {
+                         void *args[] = { nullptr }; // for `void` return value
+                         slot->call(nullptr, args);
+                     });
+    QObject::connect(watcher, &QObjectContinuationWrapper::run, watcher, &QObject::deleteLater);
+    QObject::connect(context, &QObject::destroyed, watcher, destroyWatcher);
+
+    fi.setContinuation([watcherMutex, watcher = QPointer(watcher)]
+                       (const QFutureInterfaceBase &parentData)
+    {
+        Q_UNUSED(parentData);
+        QMutexLocker lock(watcherMutex.get());
+        if (watcher)
+            emit watcher->run();
+    });
+}
+
 QFutureCallOutInterface::~QFutureCallOutInterface()
     = default;
 
@@ -105,6 +161,13 @@ void QFutureInterfaceBase::cancel(QFutureInterfaceBase::CancelMode mode)
         break;
     }
 
+    // Cancel the continuations chain
+    QFutureInterfaceBasePrivate *next = d->continuationData;
+    while (next) {
+        next->continuationState = QFutureInterfaceBasePrivate::Canceled;
+        next = next->continuationData;
+    }
+
     d->waitCondition.wakeAll();
     d->pausedWaitCondition.wakeAll();
 
@@ -611,7 +674,6 @@ void QFutureInterfaceBase::reset()
 {
     d->m_progressValue = 0;
     d->m_progress.reset();
-    d->setState(QFutureInterfaceBase::NoState);
     d->progressTime.invalidate();
     d->isValid = false;
 }
@@ -719,7 +781,7 @@ void QFutureInterfaceBasePrivate::sendCallOut(const QFutureCallOutEvent &callOut
     if (outputConnections.isEmpty())
         return;
 
-    for (int i = 0; i < outputConnections.count(); ++i)
+    for (int i = 0; i < outputConnections.size(); ++i)
         outputConnections.at(i)->postCallOutEvent(callOutEvent);
 }
 
@@ -729,38 +791,37 @@ void QFutureInterfaceBasePrivate::sendCallOuts(const QFutureCallOutEvent &callOu
     if (outputConnections.isEmpty())
         return;
 
-    for (int i = 0; i < outputConnections.count(); ++i) {
-        QFutureCallOutInterface *interface = outputConnections.at(i);
-        interface->postCallOutEvent(callOutEvent1);
-        interface->postCallOutEvent(callOutEvent2);
+    for (int i = 0; i < outputConnections.size(); ++i) {
+        QFutureCallOutInterface *iface = outputConnections.at(i);
+        iface->postCallOutEvent(callOutEvent1);
+        iface->postCallOutEvent(callOutEvent2);
     }
 }
 
 // This function connects an output interface (for example a QFutureWatcher)
 // to this future. While holding the lock we check the state and ready results
-// and add the appropriate callouts to the queue. In order to avoid deadlocks,
-// the actual callouts are made at the end while not holding the lock.
-void QFutureInterfaceBasePrivate::connectOutputInterface(QFutureCallOutInterface *interface)
+// and add the appropriate callouts to the queue.
+void QFutureInterfaceBasePrivate::connectOutputInterface(QFutureCallOutInterface *iface)
 {
     QMutexLocker locker(&m_mutex);
 
     const auto currentState = state.loadRelaxed();
     if (currentState & QFutureInterfaceBase::Started) {
-        interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Started));
+        iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Started));
         if (m_progress) {
-            interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ProgressRange,
-                                                            m_progress->minimum,
-                                                            m_progress->maximum));
-            interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Progress,
-                                                            m_progressValue,
-                                                            m_progress->text));
+            iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ProgressRange,
+                                                        m_progress->minimum,
+                                                        m_progress->maximum));
+            iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Progress,
+                                                        m_progressValue,
+                                                        m_progress->text));
         } else {
-            interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ProgressRange,
-                                                            0,
-                                                            0));
-            interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Progress,
-                                                            m_progressValue,
-                                                            QString()));
+            iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ProgressRange,
+                                                        0,
+                                                        0));
+            iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Progress,
+                                                        m_progressValue,
+                                                        QString()));
         }
     }
 
@@ -769,36 +830,36 @@ void QFutureInterfaceBasePrivate::connectOutputInterface(QFutureCallOutInterface
         while (it != data.m_results.end()) {
             const int begin = it.resultIndex();
             const int end = begin + it.batchSize();
-            interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ResultsReady,
-                                                            begin,
-                                                            end));
+            iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::ResultsReady,
+                                                        begin,
+                                                        end));
             it.batchedAdvance();
         }
     }
 
     if (currentState & QFutureInterfaceBase::Suspended)
-        interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Suspended));
+        iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Suspended));
     else if (currentState & QFutureInterfaceBase::Suspending)
-        interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Suspending));
+        iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Suspending));
 
     if (currentState & QFutureInterfaceBase::Canceled)
-        interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
+        iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
 
     if (currentState & QFutureInterfaceBase::Finished)
-        interface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Finished));
+        iface->postCallOutEvent(QFutureCallOutEvent(QFutureCallOutEvent::Finished));
 
-    outputConnections.append(interface);
+    outputConnections.append(iface);
 }
 
-void QFutureInterfaceBasePrivate::disconnectOutputInterface(QFutureCallOutInterface *interface)
+void QFutureInterfaceBasePrivate::disconnectOutputInterface(QFutureCallOutInterface *iface)
 {
     QMutexLocker lock(&m_mutex);
-    const int index = outputConnections.indexOf(interface);
+    const qsizetype index = outputConnections.indexOf(iface);
     if (index == -1)
         return;
     outputConnections.removeAt(index);
 
-    interface->callOutInterfaceDisconnected();
+    iface->callOutInterfaceDisconnected();
 }
 
 void QFutureInterfaceBasePrivate::setState(QFutureInterfaceBase::State newState)
@@ -816,45 +877,60 @@ void QFutureInterfaceBase::setContinuation(std::function<void(const QFutureInter
 {
     QMutexLocker lock(&d->continuationMutex);
 
-    if (continuationFutureData)
-        continuationFutureData->parentData = d;
-
     // If the state is ready, run continuation immediately,
     // otherwise save it for later.
     if (isFinished()) {
         lock.unlock();
         func(*this);
-    } else {
+        lock.relock();
+    }
+    // Unless the continuation has been cleaned earlier, we have to
+    // store the move-only continuation, to guarantee that the associated
+    // future's data stays alive.
+    if (d->continuationState != QFutureInterfaceBasePrivate::Cleaned) {
+        if (d->continuation) {
+            qWarning() << "Adding a continuation to a future which already has a continuation. "
+                          "The existing continuation is overwritten.";
+        }
         d->continuation = std::move(func);
+        d->continuationData = continuationFutureData;
     }
 }
 
+void QFutureInterfaceBase::cleanContinuation()
+{
+    if (!d)
+        return;
+
+    QMutexLocker lock(&d->continuationMutex);
+    d->continuation = nullptr;
+    d->continuationState = QFutureInterfaceBasePrivate::Cleaned;
+    d->continuationData = nullptr;
+}
+
 void QFutureInterfaceBase::runContinuation() const
 {
     QMutexLocker lock(&d->continuationMutex);
     if (d->continuation) {
-        auto fn = std::exchange(d->continuation, nullptr);
+        // Save the continuation in a local function, to avoid calling
+        // a null std::function below, in case cleanContinuation() is
+        // called from some other thread right after unlock() below.
+        auto fn = std::move(d->continuation);
         lock.unlock();
         fn(*this);
+
+        lock.relock();
+        // Unless the continuation has been cleaned earlier, we have to
+        // store the move-only continuation, to guarantee that the associated
+        // future's data stays alive.
+        if (d->continuationState != QFutureInterfaceBasePrivate::Cleaned)
+            d->continuation = std::move(fn);
     }
 }
 
 bool QFutureInterfaceBase::isChainCanceled() const
 {
-    if (isCanceled())
-        return true;
-
-    auto parent = d->parentData;
-    while (parent) {
-        // If the future is in Canceled state because it had an exception, we want to
-        // continue checking the chain of parents for cancellation, otherwise if the exception
-        // is handled inside the chain, it won't be interrupted even though cancellation has
-        // been requested.
-        if ((parent->state.loadRelaxed() & Canceled) && !parent->hasException)
-            return true;
-        parent = parent->parentData;
-    }
-    return false;
+    return isCanceled() || d->continuationState == QFutureInterfaceBasePrivate::Canceled;
 }
 
 void QFutureInterfaceBase::setLaunchAsync(bool value)
@@ -867,4 +943,19 @@ bool QFutureInterfaceBase::launchAsync() const
     return d->launchAsync;
 }
 
+namespace QtFuture {
+
+QFuture<void> makeReadyVoidFuture()
+{
+    QFutureInterface<void> promise;
+    promise.reportStarted();
+    promise.reportFinished();
+
+    return promise.future();
+}
+
+} // namespace QtFuture
+
 QT_END_NAMESPACE
+
+#include "qfutureinterface.moc"