From 076297eeeee7d83fe65b9eb7f883c7effc5dbf6f Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Wed, 21 Dec 2022 21:12:58 +0100
Subject: [PATCH] QFuture: port from QSharedPointer to std::shared_ptr

Compared to std::shared_ptr, QSharedPointer requires 2x the atomic
operations per copy, and this code uses _a lot_ of copies.

Port to std::shared_ptr. The uses are all in inline, non-exported
code, so there's no BC or SC issue here. Old code will happily
continue to use its QSharedPointer-based code, while recompiled code
will enjoy the transparent efficiency gain.

This also helps prepare QtCore for an eventual QT_NO_SHARED_POINTER
(which QtCore will not be able to set on itself, because QPointer is
still not ported away from QWeakPointer, but which should affect as
few headers as possible).

Change-Id: I8159c38d93f3bcfc22a236c8c26541ab5ee4e6d0
Reviewed-by: Sona Kurazyan <kurazyan.sona@gmail.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit 85b15b101c70b962fd0030c26159ef7b1b50a1f4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---
 src/corelib/thread/qfuture_impl.h | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/src/corelib/thread/qfuture_impl.h b/src/corelib/thread/qfuture_impl.h
index 6bf3a7406a5..9a60348e3de 100644
--- a/src/corelib/thread/qfuture_impl.h
+++ b/src/corelib/thread/qfuture_impl.h
@@ -17,6 +17,8 @@
 #include <QtCore/qpointer.h>
 #include <QtCore/qpromise.h>
 
+#include <memory>
+
 QT_BEGIN_NAMESPACE
 
 //
@@ -1058,7 +1060,7 @@ struct WhenAnyContext
 };
 
 template<qsizetype Index, typename ContextType, typename... Ts>
-void addCompletionHandlersImpl(const QSharedPointer<ContextType> &context,
+void addCompletionHandlersImpl(const std::shared_ptr<ContextType> &context,
                                const std::tuple<Ts...> &t)
 {
     auto future = std::get<Index>(t);
@@ -1074,7 +1076,7 @@ void addCompletionHandlersImpl(const QSharedPointer<ContextType> &context,
 }
 
 template<typename ContextType, typename... Ts>
-void addCompletionHandlers(const QSharedPointer<ContextType> &context, const std::tuple<Ts...> &t)
+void addCompletionHandlers(const std::shared_ptr<ContextType> &context, const std::tuple<Ts...> &t)
 {
     constexpr qsizetype size = std::tuple_size<std::tuple<Ts...>>::value;
     addCompletionHandlersImpl<size - 1, ContextType, Ts...>(context, t);
@@ -1087,7 +1089,7 @@ QFuture<OutputSequence> whenAllImpl(InputIt first, InputIt last)
     if (size == 0)
         return QtFuture::makeReadyFuture(OutputSequence());
 
-    auto context = QSharedPointer<QtPrivate::WhenAllContext<OutputSequence>>::create(size);
+    const auto context = std::make_shared<QtPrivate::WhenAllContext<OutputSequence>>(size);
     context->futures.resize(size);
     context->promise.start();
 
@@ -1106,7 +1108,7 @@ template<typename OutputSequence, typename... Futures>
 QFuture<OutputSequence> whenAllImpl(Futures &&... futures)
 {
     constexpr qsizetype size = sizeof...(Futures);
-    auto context = QSharedPointer<QtPrivate::WhenAllContext<OutputSequence>>::create(size);
+    const auto context = std::make_shared<QtPrivate::WhenAllContext<OutputSequence>>(size);
     context->futures.resize(size);
     context->promise.start();
 
@@ -1128,7 +1130,7 @@ QFuture<QtFuture::WhenAnyResult<typename Future<ValueType>::type>> whenAnyImpl(I
                 QtFuture::WhenAnyResult { qsizetype(-1), QFuture<PackagedType>() });
     }
 
-    auto context = QSharedPointer<QtPrivate::WhenAnyContext<ResultType>>::create();
+    const auto context = std::make_shared<QtPrivate::WhenAnyContext<ResultType>>();
     context->promise.start();
 
     qsizetype idx = 0;
@@ -1147,7 +1149,7 @@ QFuture<std::variant<std::decay_t<Futures>...>> whenAnyImpl(Futures &&... future
 {
     using ResultType = std::variant<std::decay_t<Futures>...>;
 
-    auto context = QSharedPointer<QtPrivate::WhenAnyContext<ResultType>>::create();
+    const auto context = std::make_shared<QtPrivate::WhenAnyContext<ResultType>>();
     context->promise.start();
 
     QtPrivate::addCompletionHandlers(context, std::make_tuple(std::forward<Futures>(futures)...));