4 files changed, 49 insertions, 8 deletions

diff --git a/src/corelib/thread/qfutureinterface.h b/src/corelib/thread/qfutureinterface.h
index 6c7c511cc0..9296c63f0b 100644
--- a/src/corelib/thread/qfutureinterface.h
+++ b/src/corelib/thread/qfutureinterface.h
@@ -270,11 +270,12 @@ inline void QFutureInterface<T>::reportResult(const T *result, int index)
 
     if (store.filterMode()) {
         const int resultCountBefore = store.count();
-        store.addResult<T>(index, result);
-        this->reportResultsReady(resultCountBefore, store.count());
+        if (store.addResult<T>(index, result) != -1)
+            this->reportResultsReady(resultCountBefore, store.count());
     } else {
         const int insertIndex = store.addResult<T>(index, result);
-        this->reportResultsReady(insertIndex, insertIndex + 1);
+        if (insertIndex != -1)
+            this->reportResultsReady(insertIndex, insertIndex + 1);
     }
 }
 
@@ -289,7 +290,8 @@ void QFutureInterface<T>::reportAndMoveResult(T &&result, int index)
 
     const int oldResultCount = store.count();
     const int insertIndex = store.moveResult(index, std::forward<T>(result));
-    if (!store.filterMode() || oldResultCount < store.count()) // Let's make sure it's not in pending results.
+    // Let's make sure it's not in pending results.
+    if (insertIndex != -1 && (!store.filterMode() || oldResultCount < store.count()))
         reportResultsReady(insertIndex, store.count());
 }
 
@@ -317,11 +319,12 @@ inline void QFutureInterface<T>::reportResults(const QList<T> &_results, int beg
 
     if (store.filterMode()) {
         const int resultCountBefore = store.count();
-        store.addResults(beginIndex, &_results, count);
-        this->reportResultsReady(resultCountBefore, store.count());
+        if (store.addResults(beginIndex, &_results, count) != -1)
+            this->reportResultsReady(resultCountBefore, store.count());
     } else {
         const int insertIndex = store.addResults(beginIndex, &_results, count);
-        this->reportResultsReady(insertIndex, insertIndex + _results.count());
+        if (insertIndex != -1)
+            this->reportResultsReady(insertIndex, insertIndex + _results.count());
     }
 }
 
diff --git a/src/corelib/thread/qpromise.qdoc b/src/corelib/thread/qpromise.qdoc
index 9c7925da95..4b7b497b3f 100644
--- a/src/corelib/thread/qpromise.qdoc
+++ b/src/corelib/thread/qpromise.qdoc
@@ -112,6 +112,9 @@
     Adds \a result to the internal result collection at \a index position. If
     index is unspecified, \a result is added to the end of the collection.
 
+    \note addResult() rejects \a result if there's already another result in the
+    collection stored at the same index.
+
     You can get a result at a specific index by calling QFuture::resultAt().
 
     \note It is possible to specify an arbitrary index and request result at
diff --git a/src/corelib/thread/qresultstore.cpp b/src/corelib/thread/qresultstore.cpp
index b6af27dfa9..a239954dbe 100644
--- a/src/corelib/thread/qresultstore.cpp
+++ b/src/corelib/thread/qresultstore.cpp
@@ -144,6 +144,11 @@ bool ResultIteratorBase::canIncrementVectorIndex() const
     return (m_vectorIndex + 1 < mapIterator.value().m_count);
 }
 
+bool ResultIteratorBase::isValid() const
+{
+    return mapIterator.value().isValid();
+}
+
 ResultStoreBase::ResultStoreBase()
     : insertIndex(0), resultCount(0), m_filterMode(false), filteredResults(0) { }
 
@@ -196,6 +201,15 @@ int ResultStoreBase::insertResultItem(int index, ResultItem &resultItem)
     return storeIndex;
 }
 
+bool ResultStoreBase::containsValidResultItem(int index) const
+{
+    // index might refer to either visible or pending result
+    const bool inPending = m_filterMode && index != -1 && index > insertIndex;
+    const auto &store = inPending ? pendingResults : m_results;
+    auto it = findResult(store, index);
+    return it != ResultIteratorBase(store.end()) && it.isValid();
+}
+
 void ResultStoreBase::syncPendingResults()
 {
     // check if we can insert any of the pending results:
diff --git a/src/corelib/thread/qresultstore.h b/src/corelib/thread/qresultstore.h
index 5f8c7f150a..0a1382fd79 100644
--- a/src/corelib/thread/qresultstore.h
+++ b/src/corelib/thread/qresultstore.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -87,6 +87,8 @@ public:
     bool operator!=(const ResultIteratorBase &other) const;
     bool isVector() const;
     bool canIncrementVectorIndex() const;
+    bool isValid() const;
+
 protected:
     QMap<int, ResultItem>::const_iterator mapIterator;
     int m_vectorIndex;
@@ -139,6 +141,7 @@ public:
 protected:
     int insertResultItem(int index, ResultItem &resultItem);
     void insertResultItemIfValid(int index, ResultItem &resultItem);
+    bool containsValidResultItem(int index) const;
     void syncPendingResults();
     void syncResultCount();
     int updateInsertIndex(int index, int _count);
@@ -169,6 +172,9 @@ public:
     template <typename T>
     int addResult(int index, const T *result)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         if (result == nullptr)
             return addResult(index, static_cast<void *>(nullptr));
 
@@ -178,18 +184,27 @@ public:
     template <typename T>
     int moveResult(int index, T &&result)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         return addResult(index, static_cast<void *>(new T(std::move_if_noexcept(result))));
     }
 
     template<typename T>
     int addResults(int index, const QList<T> *results)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         return addResults(index, new QList<T>(*results), results->count(), results->count());
     }
 
     template<typename T>
     int addResults(int index, const QList<T> *results, int totalCount)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         if (m_filterMode == true && results->count() != totalCount && 0 == results->count())
             return addResults(index, nullptr, 0, totalCount);
 
@@ -198,12 +213,18 @@ public:
 
     int addCanceledResult(int index)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         return addResult(index, static_cast<void *>(nullptr));
     }
 
     template <typename T>
     int addCanceledResults(int index, int _count)
     {
+        if (containsValidResultItem(index)) // reject if already present
+            return -1;
+
         QList<T> empty;
         return addResults(index, &empty, _count);
     }