From 8f89bbaf8ea463f4065d7d55b53a0f146d0e98af Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Wed, 9 Apr 2025 12:09:52 -0700
Subject: [PATCH] QReadWriteLock: add qYieldCpu() calls to the contended loop
 acquisitions

We're looping on fastTryLock() (which does testAndSetAcquire()) and a
few other testAndSet()s, so we should yield the CPU between
calls.

Change-Id: I6ba01efc9142f8be2bf1fffddf06c027dde18016
Reviewed-by: David Faure <david.faure@kdab.com>
---
 src/corelib/thread/qreadwritelock.cpp | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/corelib/thread/qreadwritelock.cpp b/src/corelib/thread/qreadwritelock.cpp
index 186a0757e99..46e6ceb887d 100644
--- a/src/corelib/thread/qreadwritelock.cpp
+++ b/src/corelib/thread/qreadwritelock.cpp
@@ -201,6 +201,7 @@ Q_NEVER_INLINE static bool contendedTryLockForRead(QAtomicPointer<QReadWriteLock
                                                    QDeadlineTimer timeout, QReadWriteLockPrivate *d)
 {
     while (true) {
+        qYieldCpu();
         if (d == nullptr) {
             if (fastTryLock(d_ptr, dummyLockedForRead, d))
                 return true;
@@ -318,6 +319,7 @@ Q_NEVER_INLINE static bool contendedTryLockForWrite(QAtomicPointer<QReadWriteLoc
                                                     QDeadlineTimer timeout, QReadWriteLockPrivate *d)
 {
     while (true) {
+        qYieldCpu();
         if (d == nullptr) {
             if (fastTryLock(d_ptr, dummyLockedForWrite, d))
                 return true;