10 files changed, 111 insertions, 339 deletions
diff --git a/doc/global/externalsites/external-resources.qdoc b/doc/global/externalsites/external-resources.qdoc
index 7a04cca52ce..8670305b00c 100644
--- a/doc/global/externalsites/external-resources.qdoc
+++ b/doc/global/externalsites/external-resources.qdoc
@@ -58,68 +58,27 @@
 */
 
 /*!
-    \externalpage https://www.freedesktop.org/wiki/Standards/xembed-spec/
-    \title XEmbed Specification
-*/
-
-/*!
-    \externalpage https://www.freedesktop.org/wiki/Standards/icon-theme-spec/
-    \title Icon Themes Specification
-*/
-
-/*!
     \externalpage https://www.cups.org/
     \title Common Unix Printing System (CUPS)
     \keyword CUPS
 */
 
 /*!
-    \externalpage https://www.freedesktop.org/wiki/Specifications/desktop-entry-spec/
-    \title Desktop Entry Specification
-*/
-
-/*!
-    \externalpage https://kde.org/
-    \title The K Desktop Environment
-    \keyword KDE
-*/
-
-/*!
     \externalpage https://cmake.org/cmake/help/latest/
     \title CMake Documentation
 */
 
 /*!
-    \externalpage https://cmake.org/cmake/help/latest/command/find_package.html
-    \title CMake find_package Documentation
-*/
-
-/*!
     \externalpage https://cmake.org/cmake/help/latest/manual/cmake-qt.7.html#automoc
     \title CMake AUTOMOC Documentation
 */
 
 /*!
-    \externalpage https://cmake.org/cmake/help/latest/manual/cmake-qt.7.html#autorcc
-    \title CMake AUTORCC Documentation
-*/
-
-/*!
     \externalpage https://cmake.org/cmake/help/latest/manual/cmake-qt.7.html#autouic
     \title CMake AUTOUIC Documentation
 */
 
 /*!
-    \externalpage https://cmake.org/cmake/help/latest/prop_tgt/LOCATION.html
-    \title CMake LOCATION Documentation
-*/
-
-/*!
-    \externalpage https://cmake.org/cmake/help/latest/prop_tgt/POSITION_INDEPENDENT_CODE.html
-    \title CMake POSITION_INDEPENDENT_CODE Documentation
-*/
-
-/*!
     \externalpage https://cmake.org/cmake/help/latest/command/target_link_libraries.html
     \title CMake target_link_libraries Documentation
 */
@@ -130,50 +89,11 @@
 */
 
 /*!
-    \externalpage https://conan.io/
-    \title Conan
-*/
-
-/*!
     \externalpage https://www.gnome.org/
     \title GNOME
 */
 
 /*!
-    \externalpage https://www.gnu.org/software/emacs/
-    \title GNU Emacs
-*/
-
-/*!
-    \externalpage https://gnuwin32.sourceforge.net/packages.html
-    \title GnuWin32 Project
-*/
-
-/*!
-    \externalpage https://www.w3.org/Graphics/SVG/About.html
-    \title About SVG
-    \keyword Scalable Vector Graphics
-*/
-
-/*!
-    \externalpage https://www.w3.org/TR/SVG/types.html#ColorKeywords
-    \title SVG color keyword names
-*/
-
-/*!
-    \externalpage https://www.w3.org/Graphics/SVG/
-    \title SVG Working Group
-*/
-
-/*!
-    \externalpage https://www.w3.org/TR/SVGMobile/
-    \title Mobile SVG Profiles
-    \omit
-    Mobile SVG Profiles: SVG Tiny and SVG Basic
-    \endomit
-*/
-
-/*!
     \externalpage https://www.w3.org/TR/SVGMobile12/
     \title SVG 1.2 Tiny
 */
@@ -186,36 +106,16 @@
 
 
 /*!
-    \externalpage https://jmeubank.github.io/tdm-gcc/
-    \title TDM-GCC
-*/
-
-/*!
     \externalpage https://www.dependencywalker.com/
     \title Dependency Walker
 */
 
 /*!
-    \externalpage https://webkit.org/
-    \title WebKit Open Source Project
-*/
-
-/*!
-    \externalpage https://www.informit.com/store/c-plus-plus-gui-programming-with-qt4-9780132354165
-    \title C++ GUI Programming with Qt 4, 2nd Edition
-*/
-
-/*!
     \externalpage https://www.openssl.org/
     \title OpenSSL Toolkit
 */
 
 /*!
-    \externalpage https://www.activestate.com/platform/supported-languages/perl/
-    \title ActivePerl
-*/
-
-/*!
     \externalpage https://chromium.googlesource.com/angle/angle/+/master/README.md
     \title ANGLE
 */
@@ -226,16 +126,6 @@
 */
 
 /*!
-    \externalpage https://www.w3.org/TR/html401/
-    \title HTML 4
-*/
-
-/*!
-    \externalpage https://html.spec.whatwg.org/multipage/
-    \title HTML 5
-*/
-
-/*!
     \externalpage https://icu.unicode.org/
     \title ICU
 */
@@ -251,41 +141,16 @@
 */
 
 /*!
-    \externalpage https://pyxml.sourceforge.net/topics/xbel/
-    \title XML Bookmark Exchange Language Resource Page
-*/
-
-/*!
-    \externalpage https://www.w3.org/TR/xquery/#errors
-    \title error handling in the XQuery language
-*/
-
-/*!
     \externalpage https://xaos-project.github.io/
     \title XaoS
 */
 
 /*!
-    \externalpage https://www.unixodbc.org
-    \title https://www.unixodbc.org
-*/
-
-/*!
     \externalpage https://www.postgresql.org
     \title https://www.postgresql.org
 */
 
 /*!
-    \externalpage https://www.postgresql.org/docs/current/installation-platform-notes.html
-    \title PostgreSQL MinGW/Native Windows
-*/
-
-/*!
-    \externalpage https://www.freetds.org
-    \title https://www.freetds.org
-*/
-
-/*!
     \externalpage https://www.sqlite.org
     \title https://www.sqlite.org
 */
@@ -301,11 +166,6 @@
 */
 
 /*!
-    \externalpage https://tldp.org/HOWTO/Framebuffer-HOWTO.html
-    \title Framebuffer HOWTO
-*/
-
-/*!
     \externalpage https://www.w3.org/TR/scxml/
     \title State Chart XML: State Machine Notation for Control Abstraction
 */
@@ -321,71 +181,21 @@
 */
 
 /*!
-    \externalpage https://www.gnu.org/licenses/old-licenses/lgpl-2.1.html
-    \title GNU Lesser General Public License, version 2.1
-*/
-
-/*!
-    \externalpage https://www.qtcentre.org
-    \title Qt Centre
-*/
-
-/*!
     \externalpage https://kde.org
     \title KDE
 */
 
 /*!
-    \externalpage https://cplusplus.com/reference/cstring/memcpy/
-    \title C++ Reference - memcpy
-*/
-
-/*!
     \externalpage https://en.cppreference.com/w/cpp/symbol_index/chrono_literals.html
     \title chrono_literals Symbol Index
 */
 
 /*!
-    \externalpage https://www.w3.org/TR/CSS2/selector.html
-    \title Standard CSS2 selector
-*/
-
-/*!
-    \externalpage https://www.w3.org/XML/Core/#Publications
-    \title W3C XML specifications
-*/
-
-/*!
-    \externalpage https://www.w3.org/XML/Schema
-    \title XML Schema
-*/
-
-/*!
-    \externalpage https://opensource.org/license/bsd-3-clause
-    \title New and Modified BSD Licenses
-*/
-
-/*!
-    \externalpage https://ecma-international.org/publications-and-standards/standards/ecma-262/
-    \title ECMAScript Language Specification
-*/
-
-/*!
     \externalpage https://developer.mozilla.org/en-US/docs/Web/JavaScript
     \title JavaScript Resources
 */
 
 /*!
-    \externalpage https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide
-    \title JavaScript Guide
-*/
-
-/*!
-    \externalpage https://developer.mozilla.org/en-US/docs/Web/JavaScript
-    \title About JavaScript
-*/
-
-/*!
     \externalpage https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Lexical_grammar#keywords
     \title JavaScript Reserved Words
 */
@@ -406,41 +216,16 @@
 */
 
 /*!
-    \externalpage https://registry.khronos.org/OpenGL/index_gl.php
-    \title OpenGL Registry
-*/
-
-/*!
-    \externalpage https://registry.khronos.org/OpenGL/index_es.php
-    \title Khronos OpenGL ES API Registry
-*/
-
-/*!
     \externalpage https://www.khronos.org/opengl/wiki/Array_Texture
     \title Array Texture
 */
 
 /*!
-    \externalpage https://github.com/iksaif/qsslkey-p11
-    \title qsslkey example
-*/
-
-/*!
     \externalpage https://www.w3.org/TR/2009/WD-webdatabase-20091029/
     \title HTML5 Web Database API
 */
 
 /*!
-    \externalpage https://lldb.llvm.org/
-    \title The LLDB Debugger
-*/
-
-/*!
-    \externalpage https://account.qt.io/s/
-    \title Qt Account Sign-up
-*/
-
-/*!
    \externalpage https://facebook.github.io/zstd/
    \title Zstandard Site
 */
diff --git a/doc/global/externalsites/qt-webpages.qdoc b/doc/global/externalsites/qt-webpages.qdoc
index 7b659fa5295..6cbf5f377b6 100644
--- a/doc/global/externalsites/qt-webpages.qdoc
+++ b/doc/global/externalsites/qt-webpages.qdoc
@@ -17,76 +17,15 @@
     \title The Qt Company
 */
 /*!
-    \externalpage http://qt.io/licensing/
-    \title Qt Licensing Overview
-*/
-/*!
-    \externalpage http://doc.qt.io/archives/qq/
-    \title Qt Quarterly
-*/
-/*!
-    \externalpage http://doc.qt.io/archives/qq/qq19-plurals.html
-    \title Qt Quarterly: Plural Form in Translation
-*/
-/*!
     \externalpage https://code.qt.io/
     \title Public Qt Repository
 */
 /*!
-    \externalpage https://code.qt.io/cgit/%7bnon-gerrit%7d/qt-labs/qtestlib-tools.git/
-    \title qtestlib-tools
-*/
-
-/*!
-    \externalpage http://wiki.qt.io/Qt_Coding_Style
-    \title Qt Coding Style
-*/
-/*!
-    \externalpage http://doc.qt.io/archives/qt-eclipse-1.6/index.html
-    \title Eclipse Plugin
-*/
-/*!
-    \externalpage http://doc.qt.io/archives/qq/qq11-events.html
-    \title Qt Quarterly: Another Look at Events
-*/
-/*!
-    \externalpage https://www.youtube.com/watch?v=P4kv-AoAJ-Q
-    \title Livecoding video effects with Qt5
-*/
-/*!
-    \externalpage http://blog.qt.io/2012/02/29/pimp-my-video-shader-effects-and-multimedia/
-    \title Pimp my video
-*/
-/*!
-    \externalpage http://wiki.qt.io/QtMediaHub
-    \title QtMediaHub
-*/
-/*!
-    \externalpage http://wiki.qt.io/Qt_RaspberryPi
-    \title QtonPi
-*/
-
-/*!
-    \externalpage http://wiki.qt.io/jom
-    \title jom
-*/
-
-/*!
-    \externalpage http://doc.qt.io/qt-4.8
-    \title Qt 4.8 Reference Documentation
-*/
-
-/*!
     \externalpage http://wiki.qt.io/Qt_Localization
     \title external: Translating Qt Into Other Languages
 */
 
 /*!
-    \externalpage http://wiki.qt.io/Qt_Multimedia_Backends
-    \title Qt Multimedia Backends
-*/
-
-/*!
     \externalpage https://doc.qt.io/qt3dstudio/index.html
     \title Qt 3D Studio Manual
 */
diff --git a/doc/global/externalsites/rfc.qdoc b/doc/global/externalsites/rfc.qdoc
index d0c127fb41e..071977b9a0e 100644
--- a/doc/global/externalsites/rfc.qdoc
+++ b/doc/global/externalsites/rfc.qdoc
@@ -12,12 +12,6 @@
 */
 
 /*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc1179
-    \title RFC 1179
-    \keyword lpr
-*/
-
-/*!
     \externalpage https://datatracker.ietf.org/doc/html/rfc1738
     \title RFC 1738
 */
@@ -28,43 +22,16 @@
 */
 
 /*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc1928
-    \title RFC 1928
-*/
-
-/*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc1929
-    \title RFC 1929
-*/
-
-/*!
     \externalpage https://datatracker.ietf.org/doc/html/rfc2045
     \title RFC 2045
 */
 
 /*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc2109
-    \title RFC 2109
-    HTTP State Management Mechanism
-*/
-
-/*!
     \externalpage https://datatracker.ietf.org/doc/html/rfc2822
     \title RFC 2822
 */
 
 /*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc2965
-    \title RFC 2965
-    HTTP State Management Mechanism
-*/
-
-/*!
-    \externalpage https://datatracker.ietf.org/doc/html/rfc3174
-    \title RFC 3174
-*/
-
-/*!
     \externalpage https://datatracker.ietf.org/doc/html/rfc3491
     \title RFC 3491
 */
diff --git a/src/corelib/doc/src/external-resources.qdoc b/src/corelib/doc/src/external-resources.qdoc
index 2232b49bf23..5d357c65496 100644
--- a/src/corelib/doc/src/external-resources.qdoc
+++ b/src/corelib/doc/src/external-resources.qdoc
@@ -28,11 +28,6 @@
 */
 
 /*!
-    \externalpage https://marcmutz.wordpress.com/effective-qt/containers/#containers-qlist
-    \title Pros and Cons of Using QList
-*/
-
-/*!
     \externalpage https://marcmutz.wordpress.com/effective-qt/containers/
     \title Understand the Qt Containers
 */
diff --git a/src/corelib/thread/qreadwritelock.cpp b/src/corelib/thread/qreadwritelock.cpp
index 96e35dcb965..2a1af2315ca 100644
--- a/src/corelib/thread/qreadwritelock.cpp
+++ b/src/corelib/thread/qreadwritelock.cpp
@@ -234,14 +234,14 @@ QBasicReadWriteLock::contendedTryLockForRead(QDeadlineTimer timeout, void *dd)
             return d->recursiveLockForRead(timeout);
 
         auto lock = qt_unique_lock(d->mutex);
-        if (d != d_ptr.loadRelaxed()) {
+        if (QReadWriteLockPrivate *dd = d_ptr.loadAcquire(); d != dd) {
             // d_ptr has changed: this QReadWriteLock was unlocked before we had
             // time to lock d->mutex.
             // We are holding a lock to a mutex within a QReadWriteLockPrivate
             // that is already released (or even is already re-used). That's ok
             // because the QFreeList never frees them.
             // Just unlock d->mutex (at the end of the scope) and retry.
-            d = d_ptr.loadAcquire();
+            d = dd;
             continue;
         }
         return d->lockForRead(lock, timeout);
@@ -340,11 +340,11 @@ QBasicReadWriteLock::contendedTryLockForWrite(QDeadlineTimer timeout, void *dd)
             return d->recursiveLockForWrite(timeout);
 
         auto lock = qt_unique_lock(d->mutex);
-        if (d != d_ptr.loadRelaxed()) {
+        if (QReadWriteLockPrivate *dd = d_ptr.loadAcquire(); d != dd) {
             // The mutex was unlocked before we had time to lock the mutex.
             // We are holding to a mutex within a QReadWriteLockPrivate that is already released
             // (or even is already re-used) but that's ok because the QFreeList never frees them.
-            d = d_ptr.loadAcquire();
+            d = dd;
             continue;
         }
         return d->lockForWrite(lock, timeout);
diff --git a/src/gui/doc/src/external-resources.qdoc b/src/gui/doc/src/external-resources.qdoc
index 0f356dd5046..14ed0817e62 100644
--- a/src/gui/doc/src/external-resources.qdoc
+++ b/src/gui/doc/src/external-resources.qdoc
@@ -36,6 +36,7 @@
     \externalpage https://specifications.freedesktop.org/icon-naming-spec/icon-naming-spec-latest.html
     \title Freedesktop Icon Naming Specification
 */
+
 /*!
     \externalpage https://standards.freedesktop.org/icon-theme-spec/icon-theme-spec-latest.html#directory_layout
     \title Icon Theme Specification - Directory Layout
diff --git a/src/testlib/doc/src/qt-webpages.qdoc b/src/testlib/doc/src/qt-webpages.qdoc
index 611f3795ba9..b32fd4f750f 100644
--- a/src/testlib/doc/src/qt-webpages.qdoc
+++ b/src/testlib/doc/src/qt-webpages.qdoc
@@ -15,7 +15,3 @@
     \title Googletest Mocking (gMock) Framework
 */
 
-/*!
-    \externalpage https://www.itk.org/Wiki/CMake_Testing_With_CTest
-    \title CMake/Testing With CTest
-*/
diff --git a/src/widgets/doc/src/external-resources.qdoc b/src/widgets/doc/src/external-resources.qdoc
index 96117546a29..0eccc3b19d4 100644
--- a/src/widgets/doc/src/external-resources.qdoc
+++ b/src/widgets/doc/src/external-resources.qdoc
@@ -1,12 +1,6 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
-
-/*!
-    \externalpage http://developer.apple.com/documentation/UserExperience/Conceptual/OSXHIGuidelines/index.html
-    \title Apple Human Interface Guidelines
-*/
-
 /*!
     \externalpage https://rk.nvg.ntnu.no/sinclair/computers/zxspectrum/zxspectrum.htm
     \title Sinclair Spectrum
diff --git a/src/xml/doc/src/external-resources.qdoc b/src/xml/doc/src/external-resources.qdoc
index 89c30a84c47..89552477ae8 100644
--- a/src/xml/doc/src/external-resources.qdoc
+++ b/src/xml/doc/src/external-resources.qdoc
@@ -1,17 +1,6 @@
 // Copyright (C) 2016 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
-
-/*!
-    \externalpage http://www.w3.org/2000/xmlns/
-    \title http://www.w3.org/2000/xmlns/
-*/
-
-/*!
-    \externalpage http://www.saxproject.org/
-    \title SAX2 Java interface
-*/
-
 /*!
     \externalpage http://www.w3.org/TR/DOM-Level-2-Core/
     \title W3C DOM Level 2
diff --git a/tests/auto/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp b/tests/auto/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp
index 86dfa5faffc..4c089091f8d 100644
--- a/tests/auto/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp
+++ b/tests/auto/corelib/thread/qreadwritelock/tst_qreadwritelock.cpp
@@ -57,6 +57,7 @@ private slots:
     void multipleReadersLoop();
     void multipleWritersLoop();
     void multipleReadersWritersLoop();
+    void heavyLoadLocks();
     void countingTest();
     void limitedReaders();
     void deleteOnUnlock();
@@ -603,6 +604,111 @@ public:
     }
 };
 
+class HeavyLoadLockThread : public QThread
+{
+public:
+    QReadWriteLock &testRwlock;
+    const qsizetype iterations;
+    const int numThreads;
+    inline HeavyLoadLockThread(QReadWriteLock &l, qsizetype iters, int numThreads, QVector<QAtomicInt *> &counters):
+        testRwlock(l),
+        iterations(iters),
+        numThreads(numThreads),
+        counters(counters)
+    { }
+
+private:
+    QVector<QAtomicInt *> &counters;
+    QAtomicInt *getCounter(qsizetype index)
+    {
+        QReadLocker locker(&testRwlock);
+        /*
+          The index is increased monotonically, so the index
+          being requested should be always within or at the end of the
+          counters vector.
+        */
+        Q_ASSERT(index <= counters.size());
+        if (counters.size() <= index || counters[index] == nullptr) {
+            locker.unlock();
+            QWriteLocker wlocker(&testRwlock);
+            if (counters.size() <= index)
+                counters.resize(index + 1, nullptr);
+            if (counters[index] == nullptr)
+                counters[index] = new QAtomicInt(0);
+            return counters[index];
+        }
+        return counters[index];
+    }
+    void releaseCounter(qsizetype index)
+    {
+        QWriteLocker locker(&testRwlock);
+        delete counters[index];
+        counters[index] = nullptr;
+    }
+
+public:
+    void run() override
+    {
+        for (qsizetype i = 0; i < iterations; ++i) {
+            QAtomicInt *counter = getCounter(i);
+            /*
+                Here each counter is accessed by each thread
+                and increaed only once. As a result, when the
+                counter reaches numThreads, i.e. the fetched
+                value before the increment is numThreads-1,
+                we know all threads have accessed this counter
+                and we can delete it safely.
+            */
+            int prev = counter->fetchAndAddRelaxed(1);
+            if (prev == numThreads - 1) {
+#ifdef QT_BUILDING_UNDER_TSAN
+            /*
+                Under TSAN, deleting and freeing an object
+                will trigger a write operation on the memory
+                of the object. Since we used fetchAndAddRelaxed
+                to update the counter, TSAN will report a data
+                race when deleting the counter here. To avoid
+                the false positive, we simply reset the counter
+                to 0 here, with ordered semantics to establish
+                the sequence to ensure the the free-ing option
+                happens after all fetchAndAddRelaxed operations
+                in other threads.
+
+                When not building under TSAN, deleting the counter
+                will not result in any data read or written to the
+                memory region of the counter, so no data race will
+                happen.
+            */
+                counter->fetchAndStoreOrdered(0);
+#endif
+                releaseCounter(i);
+            }
+        }
+    }
+};
+
+/*
+    Multiple threads racing acquiring and releasing
+    locks on the same indices.
+*/
+
+void tst_QReadWriteLock::heavyLoadLocks()
+{
+    constexpr qsizetype iterations = 65536 * 4;
+    constexpr int numThreads = 8;
+    QVector<QAtomicInt *> counters;
+    QReadWriteLock testLock;
+    std::array<std::unique_ptr<HeavyLoadLockThread>, numThreads> threads;
+    for (auto &thread : threads)
+        thread = std::make_unique<HeavyLoadLockThread>(testLock, iterations, numThreads, counters);
+    for (auto &thread : threads)
+        thread->start();
+    for (auto &thread : threads)
+        thread->wait();
+    QVERIFY(counters.size() == iterations);
+    for (qsizetype i = 0; i < iterations; ++i)
+        QVERIFY(counters[i] == nullptr);
+}
 
 /*
     A writer acquires a read-lock, a reader locks