From c1a95d1d0c6b52337a806f49eb7e7507055bcaeb Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Thu, 27 Jul 2023 14:41:29 +0200
Subject: [PATCH] QtConcurrent::run: point return value ignorers to
 QThreadPool::start(Callable&&)

Use the new Q_NODISCARD_X macro to point users that ignore the QFuture
returned from QtConcurrent::run() to QThreadPool::start(), which does
the same thing, but doesn't return a future, so is better suited for
the fire-and-forget use-case the OP of and commentators on
QTBUG-111875 cited.

Can't pick to older branches, since Q_NODISCARD_X is 6.7+.

Task-number: QTBUG-111875
Change-Id: If0bf920ecc0fb59b9a9a9931ea9dc30f7abff1b7
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
---
 src/concurrent/qtconcurrentrun.h | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/src/concurrent/qtconcurrentrun.h b/src/concurrent/qtconcurrentrun.h
index cf153ab34e6..cbc750de84f 100644
--- a/src/concurrent/qtconcurrentrun.h
+++ b/src/concurrent/qtconcurrentrun.h
@@ -35,8 +35,11 @@ namespace QtConcurrent {
 
 namespace QtConcurrent {
 
+#define QTCONCURRENT_RUN_NODISCARD \
+    Q_NODISCARD_X("Use QThreadPool::start(Callable&&) if you don't need the returned QFuture")
+
 template <class Function, class ...Args>
-[[nodiscard]]
+QTCONCURRENT_RUN_NODISCARD
 auto run(QThreadPool *pool, Function &&f, Args &&...args)
 {
     DecayedTuple<Function, Args...> tuple { std::forward<Function>(f),
@@ -46,7 +49,7 @@ auto run(QThreadPool *pool, Function &&f, Args &&...args)
 }
 
 template <class Function, class ...Args>
-[[nodiscard]]
+QTCONCURRENT_RUN_NODISCARD
 auto run(QThreadPool *pool, std::reference_wrapper<const Function> &&functionWrapper,
          Args &&...args)
 {
@@ -55,7 +58,7 @@ auto run(QThreadPool *pool, std::reference_wrapper<const Function> &&functionWra
 }
 
 template <class Function, class ...Args>
-[[nodiscard]]
+QTCONCURRENT_RUN_NODISCARD
 auto run(Function &&f, Args &&...args)
 {
     return run(QThreadPool::globalInstance(), std::forward<Function>(f),
@@ -64,7 +67,7 @@ auto run(Function &&f, Args &&...args)
 
 // overload with a Promise Type hint, takes thread pool
 template <class PromiseType, class Function, class ...Args>
-[[nodiscard]]
+QTCONCURRENT_RUN_NODISCARD
 auto run(QThreadPool *pool, Function &&f, Args &&...args)
 {
     return (new StoredFunctionCallWithPromise<Function, PromiseType, Args...>(
@@ -73,13 +76,15 @@ auto run(QThreadPool *pool, Function &&f, Args &&...args)
 
 // overload with a Promise Type hint, uses global thread pool
 template <class PromiseType, class Function, class ...Args>
-[[nodiscard]]
+QTCONCURRENT_RUN_NODISCARD
 auto run(Function &&f, Args &&...args)
 {
     return run<PromiseType>(QThreadPool::globalInstance(), std::forward<Function>(f),
                             std::forward<Args>(args)...);
 }
 
+#undef QTCONCURRENT_RUN_NODISCARD
+
 } //namespace QtConcurrent
 
 #endif // Q_QDOC