Fix living QObject after shutdown of QCoreApplication

QThreadPool is a QObject and must be deleted if the QCoreApplication
is being destroyed to release the underlying ThreadData.
A Q_GLOBAL_STATIC won't release any memory is not able to
manually release it.

Pick-to: 5.15
Task-number: QTBUG-84234
Change-Id: Ia82bcff2b564b753ed687f025ff86fa1bed1e64c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 8 insertions, 3 deletions

diff --git a/src/corelib/thread/qthreadpool.cpp b/src/corelib/thread/qthreadpool.cpp
index 9657112abc..1478cfcb19 100644
--- a/src/corelib/thread/qthreadpool.cpp
+++ b/src/corelib/thread/qthreadpool.cpp
@@ -40,13 +40,12 @@
 #include "qthreadpool.h"
 #include "qthreadpool_p.h"
 #include "qdeadlinetimer.h"
+#include "qcoreapplication.h"
 
 #include <algorithm>
 
 QT_BEGIN_NAMESPACE
 
-Q_GLOBAL_STATIC(QThreadPool, theInstance)
-
 /*
     QThread wrapper, provides synchronization against a ThreadPool
 */
@@ -478,7 +477,13 @@ QThreadPool::~QThreadPool()
 */
 QThreadPool *QThreadPool::globalInstance()
 {
-    return theInstance();
+    static QPointer<QThreadPool> theInstance;
+    static QBasicMutex theMutex;
+
+    const QMutexLocker locker(&theMutex);
+    if (theInstance.isNull() && !QCoreApplication::closingDown())
+        theInstance = new QThreadPool();
+    return theInstance;
 }
 
 /*!