Read QThreadPool::objectName thread-safe

QThreadPool allows method calls from any thread, but QObject does not
so copy objectName so we may use it locally under our own lock.

Pick-to: 6.3 6.2
Task-number: QTBUG-99775
Change-Id: Ib28910649f5d0f9ce698c7da495069635d608d03
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

2 files changed, 10 insertions, 6 deletions

diff --git a/src/corelib/thread/qthreadpool.cpp b/src/corelib/thread/qthreadpool.cpp
index 713c436371..94b0aff451 100644
--- a/src/corelib/thread/qthreadpool.cpp
+++ b/src/corelib/thread/qthreadpool.cpp
@@ -273,13 +273,9 @@ bool QThreadPoolPrivate::tooManyThreadsActive() const
 */
 void QThreadPoolPrivate::startThread(QRunnable *runnable)
 {
-    Q_Q(QThreadPool);
     Q_ASSERT(runnable != nullptr);
     QScopedPointer<QThreadPoolThread> thread(new QThreadPoolThread(this));
-    QString objectName;
-    if (QString myName = q->objectName(); !myName.isEmpty())
-        objectName = myName;
-    else
+    if (objectName.isEmpty())
         objectName = QLatin1String("Thread (pooled)");
     thread->setObjectName(objectName);
     Q_ASSERT(!allThreads.contains(thread.data())); // if this assert hits, we have an ABA problem (deleted threads don't get removed here)
@@ -476,7 +472,14 @@ void QThreadPoolPrivate::stealAndRunRunnable(QRunnable *runnable)
 */
 QThreadPool::QThreadPool(QObject *parent)
     : QObject(*new QThreadPoolPrivate, parent)
-{ }
+{
+    Q_D(QThreadPool);
+    connect(this, &QObject::objectNameChanged, this, [d](const QString &newName) {
+        // We keep a copy of the name under our own lock, so we can access it thread-safely.
+        QMutexLocker locker(&d->mutex);
+        d->objectName = newName;
+    });
+}
 
 /*!
     Destroys the QThreadPool.
diff --git a/src/corelib/thread/qthreadpool_p.h b/src/corelib/thread/qthreadpool_p.h
index 1b6a65f69d..e82e4f16e7 100644
--- a/src/corelib/thread/qthreadpool_p.h
+++ b/src/corelib/thread/qthreadpool_p.h
@@ -176,6 +176,7 @@ public:
     QQueue<QThreadPoolThread *> expiredThreads;
     QList<QueuePage *> queue;
     QWaitCondition noActiveThreads;
+    QString objectName;
 
     int expiryTimeout = 30000;
     int requestedMaxThreadCount = QThread::idealThreadCount();  // don't use this directly