From 22d4f117bd393dfea80575b4a186ebff65c076c1 Mon Sep 17 00:00:00 2001
From: David Faure <david.faure@kdab.com>
Date: Tue, 8 Apr 2025 23:37:14 +0200
Subject: [PATCH] QReadWriteLock: extract method fastTryLock

This removes a little bit of duplication, and reduces the temptation to
remove the first part of tryLockForX as duplicated (it should remain
there for performance reasons).

Change-Id: I7ce102ceeb03b5ab4fe026b56fbba245b4c2f310
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/thread/qreadwritelock.cpp | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/src/corelib/thread/qreadwritelock.cpp b/src/corelib/thread/qreadwritelock.cpp
index 0fefc7dab69..186a0757e99 100644
--- a/src/corelib/thread/qreadwritelock.cpp
+++ b/src/corelib/thread/qreadwritelock.cpp
@@ -164,6 +164,14 @@ void QReadWriteLock::destroyRecursive(QReadWriteLockPrivate *d)
     \sa unlock(), lockForRead()
 */
 
+static Q_ALWAYS_INLINE bool fastTryLock(QAtomicPointer<QReadWriteLockPrivate> &d_ptr,
+                                        QReadWriteLockPrivate *dummyValue,
+                                        QReadWriteLockPrivate *&d)
+{
+    // Succeed fast if not contended
+    return d == nullptr && d_ptr.testAndSetAcquire(nullptr, dummyValue, d);
+}
+
 /*!
     \overload
     \since 6.6
@@ -183,9 +191,8 @@ void QReadWriteLock::destroyRecursive(QReadWriteLockPrivate *d)
 */
 bool QReadWriteLock::tryLockForRead(QDeadlineTimer timeout)
 {
-    // Fast case: non contended:
     QReadWriteLockPrivate *d = d_ptr.loadRelaxed();
-    if (d == nullptr && d_ptr.testAndSetAcquire(nullptr, dummyLockedForRead, d))
+    if (fastTryLock(d_ptr, dummyLockedForRead, d))
         return true;
     return contendedTryLockForRead(d_ptr, timeout, d);
 }
@@ -195,9 +202,9 @@ Q_NEVER_INLINE static bool contendedTryLockForRead(QAtomicPointer<QReadWriteLock
 {
     while (true) {
         if (d == nullptr) {
-            if (!d_ptr.testAndSetAcquire(nullptr, dummyLockedForRead, d))
-                continue;
-            return true;
+            if (fastTryLock(d_ptr, dummyLockedForRead, d))
+                return true;
+            continue;
         }
 
         if ((quintptr(d) & StateMask) == StateLockedForRead) {
@@ -301,9 +308,8 @@ Q_NEVER_INLINE static bool contendedTryLockForRead(QAtomicPointer<QReadWriteLock
 */
 bool QReadWriteLock::tryLockForWrite(QDeadlineTimer timeout)
 {
-    // Fast case: non contended:
     QReadWriteLockPrivate *d = d_ptr.loadRelaxed();
-    if (d == nullptr && d_ptr.testAndSetAcquire(nullptr, dummyLockedForWrite, d))
+    if (fastTryLock(d_ptr, dummyLockedForWrite, d))
         return true;
     return contendedTryLockForWrite(d_ptr, timeout, d);
 }
@@ -313,9 +319,9 @@ Q_NEVER_INLINE static bool contendedTryLockForWrite(QAtomicPointer<QReadWriteLoc
 {
     while (true) {
         if (d == nullptr) {
-            if (!d_ptr.testAndSetAcquire(d, dummyLockedForWrite, d))
-                continue;
-            return true;
+            if (fastTryLock(d_ptr, dummyLockedForWrite, d))
+                return true;
+            continue;
         }
 
         if (isUncontendedLocked(d)) {