From ce59ccb3341223cda4f7ef2469d86326c6a116e8 Mon Sep 17 00:00:00 2001
From: Sona Kurazyan <sona.kurazyan@qt.io>
Date: Wed, 6 Oct 2021 10:04:54 +0200
Subject: Optimize QPromise destructor
MIME-Version: 1.0
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Unify cancel and finish in QPromise destructor in a single call. This
saves us one extra mutex lock and atomic state change.

Task-number: QTBUG-84977
Change-Id: Iac06302c39a2863008b27325fcf6792d4f58c8ae
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
---
 src/corelib/thread/qfutureinterface.cpp | 30 ++++++++++++++++++++++++++----
 src/corelib/thread/qfutureinterface.h   |  5 +++++
 src/corelib/thread/qpromise.h           |  6 ++----
 3 files changed, 33 insertions(+), 8 deletions(-)

(limited to 'src/corelib/thread')

diff --git a/src/corelib/thread/qfutureinterface.cpp b/src/corelib/thread/qfutureinterface.cpp
index b34385897c..e640114bb0 100644
--- a/src/corelib/thread/qfutureinterface.cpp
+++ b/src/corelib/thread/qfutureinterface.cpp
@@ -109,15 +109,37 @@ static inline int switch_from_to(QAtomicInt &a, int from, int to)
 }
 
 void QFutureInterfaceBase::cancel()
+{
+    cancel(CancelMode::CancelOnly);
+}
+
+void QFutureInterfaceBase::cancel(QFutureInterfaceBase::CancelMode mode)
 {
     QMutexLocker locker(&d->m_mutex);
-    if (d->state.loadRelaxed() & Canceled)
-        return;
 
-    switch_from_to(d->state, suspendingOrSuspended, Canceled);
+    const auto oldState = d->state.loadRelaxed();
+
+    switch (mode) {
+    case CancelMode::CancelAndFinish:
+        if ((oldState & Finished) && (oldState & Canceled))
+            return;
+        switch_from_to(d->state, suspendingOrSuspended | Running, Canceled | Finished);
+        break;
+    case CancelMode::CancelOnly:
+        if (oldState & Canceled)
+            return;
+        switch_from_to(d->state, suspendingOrSuspended, Canceled);
+        break;
+    }
+
     d->waitCondition.wakeAll();
     d->pausedWaitCondition.wakeAll();
-    d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
+
+    if (!(oldState & Canceled))
+        d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Canceled));
+    if (mode == CancelMode::CancelAndFinish && !(oldState & Finished))
+        d->sendCallOut(QFutureCallOutEvent(QFutureCallOutEvent::Finished));
+
     d->isValid = false;
 }
 
diff --git a/src/corelib/thread/qfutureinterface.h b/src/corelib/thread/qfutureinterface.h
index ecc31d6ec3..e813031d59 100644
--- a/src/corelib/thread/qfutureinterface.h
+++ b/src/corelib/thread/qfutureinterface.h
@@ -154,6 +154,8 @@ public:
     int loadState() const;
 
     void cancel();
+    void cancelAndFinish() { cancel(CancelMode::CancelAndFinish); }
+
     void setSuspended(bool suspend);
     void toggleSuspended();
     void reportSuspended() const;
@@ -216,6 +218,9 @@ protected:
     bool launchAsync() const;
 
     bool isRunningOrPending() const;
+
+    enum class CancelMode { CancelOnly, CancelAndFinish };
+    void cancel(CancelMode mode);
 };
 
 inline void swap(QFutureInterfaceBase &lhs, QFutureInterfaceBase &rhs) noexcept
diff --git a/src/corelib/thread/qpromise.h b/src/corelib/thread/qpromise.h
index a1ac8eaf27..3cecbd8306 100644
--- a/src/corelib/thread/qpromise.h
+++ b/src/corelib/thread/qpromise.h
@@ -70,10 +70,8 @@ public:
             return;
         // Otherwise, if computation is not finished at this point, cancel
         // potential waits
-        if (!(state & QFutureInterfaceBase::State::Finished)) {
-            d.cancel();
-            finish();  // required to finalize the state
-        }
+        if (!(state & QFutureInterfaceBase::State::Finished))
+            d.cancelAndFinish(); // cancel and finalize the state
     }
 
     // Core QPromise APIs
-- 
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