QtConcurrent: Integrate runWithPromise into run

Change-Id: I6eb95aa66ff847e8bb9aac348fded3a5d55015b6
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

5 files changed, 153 insertions, 147 deletions

diff --git a/src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentrun.cpp b/src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentrun.cpp
index 60d276cde6..bf39119c51 100644
--- a/src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentrun.cpp
+++ b/src/concurrent/doc/snippets/code/src_concurrent_qtconcurrentrun.cpp
@@ -147,7 +147,7 @@ QtConcurrent::run(&o, 42).waitForFinished(); // compilation error
 
 //! [9]
 extern void aFunction(QPromise<void> &promise);
-QFuture<void> future = QtConcurrent::runWithPromise(aFunction);
+QFuture<void> future = QtConcurrent::run(aFunction);
 //! [9]
 
 //! [10]
@@ -156,7 +156,7 @@ extern void aFunction(QPromise<void> &promise, int arg1, const QString &arg2);
 int integer = ...;
 QString string = ...;
 
-QFuture<void> future = QtConcurrent::runWithPromise(aFunction, integer, string);
+QFuture<void> future = QtConcurrent::run(aFunction, integer, string);
 //! [10]
 
 //! [11]
@@ -166,7 +166,7 @@ void helloWorldFunction(QPromise<QString> &promise)
     promise.addResult("world");
 }
 
-QFuture<QString> future = QtConcurrent::runWithPromise(helloWorldFunction);
+QFuture<QString> future = QtConcurrent::run(helloWorldFunction);
 ...
 QList<QString> results = future.results();
 //! [11]
@@ -185,7 +185,7 @@ void aFunction(QPromise<int> &promise)
     }
 }
 
-QFuture<int> future = QtConcurrent::runWithPromise(aFunction);
+QFuture<int> future = QtConcurrent::run(aFunction);
 
 ... // user pressed a pause button after 10 seconds
 future.suspend();
@@ -216,7 +216,7 @@ QObject::connect(&watcher, &QFutureWatcher::progressValueChanged, [](int progres
     ... ; // update GUI with a progress
     qDebug() << "current progress:" << progress;
 });
-watcher.setFuture(QtConcurrent::runWithPromise(aFunction));
+watcher.setFuture(QtConcurrent::run(aFunction));
 //! [13]
 
 //! [14]
@@ -226,7 +226,7 @@ struct Functor {
 };
 
 Functor f;
-runWithPromise<double>(f); // this will select the 2nd overload
-// runWithPromise(f);      // error, both candidate overloads potentially match
+run<double>(f); // this will select the 2nd overload
+// run(f);      // error, both candidate overloads potentially match
 //! [14]
 
diff --git a/src/concurrent/doc/src/qtconcurrent-index.qdoc b/src/concurrent/doc/src/qtconcurrent-index.qdoc
index f9b6375b4e..8507d77f9d 100644
--- a/src/concurrent/doc/src/qtconcurrent-index.qdoc
+++ b/src/concurrent/doc/src/qtconcurrent-index.qdoc
@@ -81,15 +81,10 @@
             folded into a single result.
     \endlist
 
-    \li \l {Concurrent Run and Run With Promise}
+    \li \l {Concurrent Run}
     \list
         \li \l {QtConcurrent::run}{QtConcurrent::run()} runs a function in
             another thread.
-        \li \l {QtConcurrent::runWithPromise}{QtConcurrent::runWithPromise()}
-            is like run(), except that the function to run accepts additional
-            argument of QPromise type that enables more control over the function
-            execution, like suspending or canceling the execution when requested,
-            progress reporting or reporting multiple results.
     \endlist
 
     \li \l {Concurrent Task}
diff --git a/src/concurrent/qtconcurrentrun.cpp b/src/concurrent/qtconcurrentrun.cpp
index fecbb484ff..978bc8cd8d 100644
--- a/src/concurrent/qtconcurrentrun.cpp
+++ b/src/concurrent/qtconcurrentrun.cpp
@@ -39,22 +39,25 @@
 
 /*!
     \page qtconcurrentrun.html
-    \title Concurrent Run and Run With Promise
+    \title Concurrent Run
     \ingroup thread
 
-    The QtConcurrent::run() and QtConcurrent::runWithPromise()
-    functions run a function in a separate thread.
+    The QtConcurrent::run() function runs a function in a separate thread.
     The return value of the function is made available through the QFuture API.
-    The function passed to QtConcurrent::run() is able to report merely
-    a single computation result to its caller, while the function passed to
-    QtConcurrent::runWithPromise() can make use of the additional
+
+    QtConcurrent::run() is an overloaded method. You can think of these overloads as slightly
+    different \e modes.
+    In \l {Concurrent Run (basic mode)} {basic mode}, the function passed to QtConcurrent::run()
+    is able to report merely a single computation result to its caller.
+    In \l {Concurrent Run With Promise} {run with promise mode}, the function passed to
+    QtConcurrent::run() can make use of the additional
     QPromise API, which enables multiple result reporting, progress reporting,
     suspending the computation when requested by the caller, or stopping
     the computation on the caller's demand.
 
-    These functions are part of the Qt Concurrent framework.
+    This function is a part of the Qt Concurrent framework.
 
-    \section1 Concurrent Run
+    \section1 Concurrent Run (basic mode)
 
     The function passed to QtConcurrent::run() may report the result
     through its return value.
@@ -65,7 +68,7 @@
 
     \snippet code/src_concurrent_qtconcurrentrun.cpp 0
 
-    This will run \e aFunction in a separate thread obtained from the default
+    This will run \c aFunction in a separate thread obtained from the default
     QThreadPool. You can use the QFuture and QFutureWatcher classes to monitor
     the status of the function.
 
@@ -135,8 +138,8 @@
 
     \section1 Concurrent Run With Promise
 
-    The QtConcurrent::runWithPromise() enables more control
-    for the running task comparing to QtConcurrent::run().
+    The \e {Run With Promise} mode enables more control for the running
+    task compared to \e basic mode of QtConcurrent::run().
     It allows progress reporting of the running task,
     reporting multiple results, suspending the execution
     if it was requested, or canceling the task on caller's
@@ -144,16 +147,16 @@
 
     \section2 The mandatory QPromise argument
 
-    The function passed to QtConcurrent::runWithPromise() is expected
-    to have an additional argument of \e {QPromise<T> &} type, where
+    The function passed to QtConcurrent::run() in \e {Run With Promise} mode is expected
+    to have an additional argument of \c {QPromise<T> &} type, where
     T is the type of the computation result (it should match the type T
     of QFuture<T> returned by the QtConcurrent::runWithPromise()), like e.g.:
 
     \snippet code/src_concurrent_qtconcurrentrun.cpp 9
 
-    The \e promise argument is instantiated inside the
-    QtConcurrent::runWithPromise() function, and its reference
-    is passed to the invoked \e aFunction, so the user
+    The \c promise argument is instantiated inside the
+    QtConcurrent::run() function, and its reference
+    is passed to the invoked \c aFunction, so the user
     doesn't need to instantiate it by himself, nor pass it explicitly
     when calling QtConcurrent::runWithPromise().
 
@@ -164,8 +167,8 @@
 
     \section2 Reporting results
 
-    In contrast to QtConcurrent::run(), the function passed to
-    QtConcurrent::runWithPromise() is expected to always return void type.
+    In contrast to \e basic mode of QtConcurrent::run(), the function passed to
+    QtConcurrent::run() in \e {Run With Promise} mode is expected to always return void type.
     Result reporting is done through the additional argument of QPromise type.
     It also enables multiple result reporting, like:
 
@@ -177,20 +180,20 @@
 
     \snippet code/src_concurrent_qtconcurrentrun.cpp 12
 
-    The call to \e future.suspend() requests the running task to
+    The call to \c future.suspend() requests the running task to
     hold its execution. After calling this method, the running task
-    will suspend after the next call to \e promise.suspendIfRequested()
+    will suspend after the next call to \c promise.suspendIfRequested()
     in its iteration loop. In this case the running task will
-    block on a call to \e promise.suspendIfRequested(). The blocked
-    call will unblock after the \e future.resume() is called.
+    block on a call to \c promise.suspendIfRequested(). The blocked
+    call will unblock after the \c future.resume() is called.
     Note, that internally suspendIfRequested() uses wait condition
     in order to unblock, so the running thread goes into an idle state
     instead of wasting its resources when blocked in order to periodically
     check if the resume request came from the caller's thread.
 
-    The call to \e future.cancel() from the last line causes that the next
-    call to \e promise.isCanceled() will return \c true and
-    \e aFunction will return immediately without any further result reporting.
+    The call to \c future.cancel() from the last line causes that the next
+    call to \c promise.isCanceled() will return \c true and
+    \c aFunction will return immediately without any further result reporting.
 
     \section2 Progress reporting
 
@@ -199,17 +202,17 @@
 
     \snippet code/src_concurrent_qtconcurrentrun.cpp 13
 
-    The caller installs the \e QFutureWatcher for the \e QFuture
-    returned by QtConcurrent::runWithPromise() in order to
-    connect to its \e progressValueChanged() signal and update
+    The caller installs the \c QFutureWatcher for the \c QFuture
+    returned by QtConcurrent::run() in order to
+    connect to its \c progressValueChanged() signal and update
     e.g. the graphical user interface accordingly.
 
     \section2 Invoking functions with overloaded operator()()
 
-    By default, QtConcurrent::runWithPromise() doesn't support functors with
-    overloaded operator()(). In case of overloaded functors the user
-    needs to explicitly specify the result type
-    as a template parameter passed to runWithPromise, like:
+    By default, QtConcurrent::run() doesn't support functors with
+    overloaded operator()() in \e {Run With Promise} mode. In case of overloaded
+    functors the user needs to explicitly specify the result type
+    as a template parameter passed to QtConcurrent::run(), like:
 
     \snippet code/src_concurrent_qtconcurrentrun.cpp 14
 */
@@ -235,81 +238,38 @@
     QThreadPool. Note that \a function may not run immediately; \a function
     will only be run once a thread becomes available.
 
-    T is the same type as the return value of \a function. Non-void return
-    values can be accessed via the QFuture::result() function.
+//! [run-description]
+    In \l {Concurrent Run (basic mode)} {basic mode} T is the same type as the return value
+    of \a function. Non-void return values can be accessed via the QFuture::result() function.
 
-    \note The QFuture returned can only be used to query for the
-    running/finished status and the return value of the function. In particular,
+    In \l {Concurrent Run (basic mode)} {basic mode} the QFuture returned can only be used to
+    query for the running/finished status and the return value of the function. In particular,
     canceling or pausing can be issued only if the computations behind the future
     has not been started.
 
-    \sa {Concurrent Run}
-*/
-
-/*!
-    \since 5.4
-    \fn QFuture<T> QtConcurrent::run(QThreadPool *pool, Function function, ...);
-
-    Runs \a function in a separate thread. The thread is taken from the
-    QThreadPool \a pool. Note that \a function may not run immediately; \a function
-    will only be run once a thread becomes available.
-
-    T is the same type as the return value of \a function. Non-void return
-    values can be accessed via the QFuture::result() function.
-
-    \note The QFuture returned can only be used to query for the
-    running/finished status and the return value of the function. In particular,
-    canceling or pausing can be issued only if the computations behind the future
-    has not been started.
-
-    \sa {Concurrent Run}
-*/
-
-/*!
-    \since 6.0
-    \fn QFuture<T> QtConcurrent::runWithPromise(Function function, ...);
-
-    Equivalent to
-    \code
-    QtConcurrent::runWithPromise(QThreadPool::globalInstance(), function, ...);
-    \endcode
-
-    Runs \a function in a separate thread. The thread is taken from the global
-    QThreadPool. Note that \a function may not run immediately; \a function
-    will only be run once a thread becomes available.
-
-    The \a function is expected to return void
-    and must take an additional argument of \e {QPromise<T> &} type,
+    In \l {Concurrent Run With Promise} {run with promise mode}, the \a function is expected
+    to return void and must take an additional argument of \c {QPromise<T> &} type,
     placed as a first argument in function's argument list. T is the result type
-    and it is the same for the returned \e QFuture<T>.
+    and it is the same for the returned \c QFuture<T>.
 
-    Similar to QtConcurrent::run(), the QFuture returned can be used to query for the
-    running/finished status and the value reported by the function. In addition,
-    it may be used for suspending or canceling the running task, fetching
-    multiple results from the called /a function or monitoring progress
-    reported by the \a function.
+    In \l {Concurrent Run With Promise} {run with promise mode}, similar to \e basic mode, the
+    QFuture returned can be used to query for the running/finished status and the value reported
+    by the function. In addition, it may be used for suspending or canceling the
+    running task, fetching multiple results from the called \a function or
+    monitoring progress reported by the \a function.
 
-    \sa {Concurrent Run With Promise}
+    \sa {Concurrent Run (basic mode)}, {Concurrent Run With Promise}
+//! [run-description]
 */
 
 /*!
-    \since 6.0
-    \fn QFuture<T> QtConcurrent::runWithPromise(QThreadPool *pool, Function function, ...);
+    \since 5.4
+    \fn QFuture<T> QtConcurrent::run(QThreadPool *pool, Function function, ...);
 
     Runs \a function in a separate thread. The thread is taken from the
     QThreadPool \a pool. Note that \a function may not run immediately; \a function
     will only be run once a thread becomes available.
 
-    The \a function is expected to return void
-    and must take an additional argument of \e {QPromise<T> &} type,
-    placed as a first argument in function's argument list. T is the result type
-    and it is the same for the returned \e QFuture<T>.
-
-    Similar to QtConcurrent::run(), the QFuture returned can be used to query for the
-    running/finished status and the value reported by the function. In addition,
-    it may be used for suspending or canceling the running task, fetching
-    multiple results from the called /a function or monitoring progress
-    reported by the \a function.
-
-    \sa {Concurrent Run With Promise}
+    \include qtconcurrentrun.cpp run-description
 */
+
diff --git a/src/concurrent/qtconcurrentrun.h b/src/concurrent/qtconcurrentrun.h
index 79322b925f..4ce8d6ae05 100644
--- a/src/concurrent/qtconcurrentrun.h
+++ b/src/concurrent/qtconcurrentrun.h
@@ -77,55 +77,45 @@ template <class Function, class ...Args>
 [[nodiscard]]
 auto run(QThreadPool *pool, Function &&f, Args &&...args)
 {
-    return (new StoredFunctionCall<Function, Args...>(
-                std::forward<Function>(f), std::forward<Args>(args)...))->start(pool);
+    DecayedTuple<Function, Args...> tuple { std::forward<Function>(f),
+                                            std::forward<Args>(args)... };
+    return TaskResolver<std::decay_t<Function>, std::decay_t<Args>...>::run(
+                std::move(tuple), TaskStartParameters { pool });
 }
 
 template <class Function, class ...Args>
 [[nodiscard]]
-auto run(Function &&f, Args &&...args)
+auto run(QThreadPool *pool, std::reference_wrapper<const Function> &&functionWrapper,
+         Args &&...args)
 {
-    return run(QThreadPool::globalInstance(), std::forward<Function>(f), std::forward<Args>(args)...);
-}
-
-template <class PromiseType, class Function, class ...Args>
-[[nodiscard]]
-auto runWithPromise(QThreadPool *pool, Function &&f, Args &&...args)
-{
-    return (new StoredFunctionCallWithPromise<Function, PromiseType, Args...>(
-                std::forward<Function>(f), std::forward<Args>(args)...))->start(pool);
+    return run(pool, std::forward<const Function>(functionWrapper.get()),
+               std::forward<Args>(args)...);
 }
 
 template <class Function, class ...Args>
 [[nodiscard]]
-auto runWithPromise(QThreadPool *pool, Function &&f, Args &&...args)
-{
-    static_assert(QtPrivate::ArgResolver<Function>::IsPromise, "The first argument of passed callable object isn't a QPromise<T> & type.");
-    using PromiseType = typename QtPrivate::ArgResolver<Function>::PromiseType;
-    return runWithPromise<PromiseType>(pool, std::forward<Function>(f), std::forward<Args>(args)...);
-}
-
-template <class Function, class ...Args>
-[[nodiscard]]
-auto runWithPromise(QThreadPool *pool, std::reference_wrapper<const Function> &&functionWrapper, Args &&...args)
+auto run(Function &&f, Args &&...args)
 {
-    static_assert(QtPrivate::ArgResolver<const Function>::IsPromise, "The first argument of passed callable object isn't a QPromise<T> & type.");
-    using PromiseType = typename QtPrivate::ArgResolver<const Function>::PromiseType;
-    return runWithPromise<PromiseType>(pool, std::forward<const Function>(functionWrapper.get()), std::forward<Args>(args)...);
+    return run(QThreadPool::globalInstance(), std::forward<Function>(f),
+               std::forward<Args>(args)...);
 }
 
+// overload with a Promise Type hint, takes thread pool
 template <class PromiseType, class Function, class ...Args>
 [[nodiscard]]
-auto runWithPromise(Function &&f, Args &&...args)
+auto run(QThreadPool *pool, Function &&f, Args &&...args)
 {
-    return runWithPromise<PromiseType>(QThreadPool::globalInstance(), std::forward<Function>(f), std::forward<Args>(args)...);
+    return (new StoredFunctionCallWithPromise<Function, PromiseType, Args...>(
+                std::forward<Function>(f), std::forward<Args>(args)...))->start(pool);
 }
 
-template <class Function, class ...Args>
+// overload with a Promise Type hint, uses global thread pool
+template <class PromiseType, class Function, class ...Args>
 [[nodiscard]]
-auto runWithPromise(Function &&f, Args &&...args)
+auto run(Function &&f, Args &&...args)
 {
-    return runWithPromise(QThreadPool::globalInstance(), std::forward<Function>(f), std::forward<Args>(args)...);
+    return run<PromiseType>(QThreadPool::globalInstance(), std::forward<Function>(f),
+                            std::forward<Args>(args)...);
 }
 
 } //namespace QtConcurrent
diff --git a/src/concurrent/qtconcurrentstoredfunctioncall.h b/src/concurrent/qtconcurrentstoredfunctioncall.h
index 1257d70b82..f52b6e2efc 100644
--- a/src/concurrent/qtconcurrentstoredfunctioncall.h
+++ b/src/concurrent/qtconcurrentstoredfunctioncall.h
@@ -102,17 +102,21 @@ template <class IsMember, class Function, class PromiseType, class... Args>
 struct FunctionResolverHelper;
 
 template <class Function, class PromiseType, class... Args>
-struct FunctionResolverHelper<std::false_type, Function, PromiseType, Args...> : public NonMemberFunctionResolver<Function, PromiseType, Args...>
+struct FunctionResolverHelper<std::false_type, Function, PromiseType, Args...>
+        : public NonMemberFunctionResolver<Function, PromiseType, Args...>
 {
 };
 
 template <class Function, class PromiseType, class... Args>
-struct FunctionResolverHelper<std::true_type, Function, PromiseType, Args...> : public MemberFunctionResolver<Function, PromiseType, Args...>
+struct FunctionResolverHelper<std::true_type, Function, PromiseType, Args...>
+        : public MemberFunctionResolver<Function, PromiseType, Args...>
 {
 };
 
 template <class Function, class PromiseType, class... Args>
-struct FunctionResolver : public FunctionResolverHelper<typename std::is_member_function_pointer<std::decay_t<Function>>::type, Function, PromiseType, Args...>
+struct FunctionResolver
+        : public FunctionResolverHelper<typename std::is_member_function_pointer<
+                 std::decay_t<Function>>::type, Function, PromiseType, Args...>
 {
 };
 
@@ -134,10 +138,6 @@ using DecayedTuple = std::tuple<std::decay_t<Types>...>;
 template <class Function, class ...Args>
 struct StoredFunctionCall : public RunFunctionTask<InvokeResultType<Function, Args...>>
 {
-    StoredFunctionCall(Function &&f, Args &&...args)
-        : data{std::forward<Function>(f), std::forward<Args>(args)...}
-    {}
-
     StoredFunctionCall(DecayedTuple<Function, Args...> &&_data)
         : data(std::move(_data))
     {}
@@ -165,11 +165,13 @@ struct StoredFunctionCallWithPromise : public RunFunctionTaskBase<PromiseType>
     using DataType = typename Resolver::Type;
     StoredFunctionCallWithPromise(Function &&f, Args &&...args)
         : prom(this->promise),
-          data(std::move(Resolver::initData(std::forward<Function>(f), std::ref(prom), std::forward<Args>(args)...)))
+          data(std::move(Resolver::initData(std::forward<Function>(f), std::ref(prom),
+                                            std::forward<Args>(args)...)))
     {}
 
-    StoredFunctionCallWithPromise(DataType &&_data)
-        : data(std::move(_data))
+    StoredFunctionCallWithPromise(DecayedTuple<Function, Args...> &&_data)
+        : StoredFunctionCallWithPromise(std::move(_data),
+               std::index_sequence_for<std::decay_t<Function>, std::decay_t<Args>...>())
     {}
 
 protected:
@@ -179,10 +181,69 @@ protected:
     }
 
 private:
+    // helper to pack back the tuple into parameter pack
+    template<std::size_t... Is>
+    StoredFunctionCallWithPromise(DecayedTuple<Function, Args...> &&_data,
+                                  std::index_sequence<Is...>)
+        : StoredFunctionCallWithPromise(std::move(std::get<Is>(_data))...)
+    {}
+
     QPromise<PromiseType> prom;
     DataType data;
 };
 
+template<typename...>
+struct NonPromiseTaskResolver;
+
+template <typename Function, typename ... Args>
+struct NonPromiseTaskResolver<Function, Args...>
+{
+    using TaskWithArgs = DecayedTuple<Function, Args...>;
+    static auto run(TaskWithArgs &&args, const TaskStartParameters &startParameters) {
+        return (new StoredFunctionCall<Function, Args...>(std::move(args)))
+                ->start(startParameters);
+    }
+};
+
+template<typename...>
+struct PromiseTaskResolver;
+
+template <typename Function, typename ... Args>
+struct PromiseTaskResolver<Function, Args...>
+{
+    static_assert(QtPrivate::ArgResolver<Function>::IsPromise::value,
+        "The first argument of passed callable object isn't a QPromise<T> & type. "
+        "Did you intend to pass a callable which takes a QPromise<T> & type as a first argument? "
+        "Otherwise it's not possible to invoke the function with passed arguments.");
+    using TaskWithArgs = DecayedTuple<Function, Args...>;
+    static auto run(TaskWithArgs &&args, const TaskStartParameters &startParameters) {
+        using PromiseType = typename QtPrivate::ArgResolver<Function>::PromiseType;
+        return (new StoredFunctionCallWithPromise<Function, PromiseType, Args...>(std::move(args)))
+                   ->start(startParameters);
+    }
+};
+
+template <class IsDirectlyInvocable, class Function, class... Args>
+struct TaskResolverHelper;
+
+template <class Function, class... Args>
+struct TaskResolverHelper<std::true_type, Function, Args...>
+        : public NonPromiseTaskResolver<Function, Args...>
+{
+};
+
+template <class Function, class... Args>
+struct TaskResolverHelper<std::false_type, Function, Args...>
+        : public PromiseTaskResolver<Function, Args...>
+{
+};
+
+template <class Function, class... Args>
+struct TaskResolver : public TaskResolverHelper<typename std::is_invocable<std::decay_t<Function>,
+        std::decay_t<Args>...>::type, Function, Args...>
+{
+};
+
 } //namespace QtConcurrent
 
 #endif // Q_QDOC