Add a way for auxiliary threads to handle events without CoreApp

Long-lived threads started by Qt itself can now receive events even if
QCoreApplication hasn't been created. This is required in all threads we
start that will handle events, unless we're sure that the thread will
exit before the global application object begins destruction.

Otherwise, those threads will have race conditions dealing with the
event delivery system trying to call the QCoreApplication::notify()
virtual while the object is being destroyed.

Change-Id: I27eaacb532114dd188c4ffff13d4ad2a4bb443e6
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

12 files changed, 76 insertions, 12 deletions

diff --git a/src/corelib/kernel/qcoreapplication.cpp b/src/corelib/kernel/qcoreapplication.cpp
index e47dc0dff2..9ad7970807 100644
--- a/src/corelib/kernel/qcoreapplication.cpp
+++ b/src/corelib/kernel/qcoreapplication.cpp
@@ -538,6 +538,14 @@ QThread *QCoreApplicationPrivate::mainThread()
     return theMainThread;
 }
 
+bool QCoreApplicationPrivate::threadRequiresCoreApplication()
+{
+    QThreadData *data = QThreadData::current(false);
+    if (!data)
+        return true;    // default setting
+    return data->requiresCoreApplication;
+}
+
 void QCoreApplicationPrivate::checkReceiverThread(QObject *receiver)
 {
     QThread *currentThread = QThread::currentThread();
@@ -926,6 +934,8 @@ bool QCoreApplication::isQuitLockEnabled()
     return quitLockRefEnabled;
 }
 
+static bool doNotify(QObject *, QEvent *);
+
 /*!
     Enables the ability of the QEventLoopLocker feature to quit
     the application.
@@ -960,7 +970,8 @@ bool QCoreApplication::notifyInternal(QObject *receiver, QEvent *event)
 */
 bool QCoreApplication::notifyInternal2(QObject *receiver, QEvent *event)
 {
-    if (!self)
+    bool selfRequired = QCoreApplicationPrivate::threadRequiresCoreApplication();
+    if (!self && selfRequired)
         return false;
 
     // Make it possible for Qt Script to hook into events even
@@ -978,6 +989,8 @@ bool QCoreApplication::notifyInternal2(QObject *receiver, QEvent *event)
     QObjectPrivate *d = receiver->d_func();
     QThreadData *threadData = d->threadData;
     QScopedLoopLevelCounter loopLevelCounter(threadData);
+    if (!selfRequired)
+        return doNotify(receiver, event);
     return self->notify(receiver, event);
 }
 
@@ -1039,7 +1052,11 @@ bool QCoreApplication::notify(QObject *receiver, QEvent *event)
     // no events are delivered after ~QCoreApplication() has started
     if (QCoreApplicationPrivate::is_app_closing)
         return true;
+    return doNotify(receiver, event);
+}
 
+static bool doNotify(QObject *receiver, QEvent *event)
+{
     if (receiver == 0) {                        // serious error
         qWarning("QCoreApplication::notify: Unexpected null receiver");
         return true;
@@ -1054,7 +1071,10 @@ bool QCoreApplication::notify(QObject *receiver, QEvent *event)
 
 bool QCoreApplicationPrivate::sendThroughApplicationEventFilters(QObject *receiver, QEvent *event)
 {
-    if (receiver->d_func()->threadData == this->threadData && extraData) {
+    // We can't access the application event filters outside of the main thread (race conditions)
+    Q_ASSERT(receiver->d_func()->threadData->thread == mainThread());
+
+    if (extraData) {
         // application event filters are only called for objects in the GUI thread
         for (int i = 0; i < extraData->eventFilters.size(); ++i) {
             QObject *obj = extraData->eventFilters.at(i);
@@ -1097,7 +1117,9 @@ bool QCoreApplicationPrivate::sendThroughObjectEventFilters(QObject *receiver, Q
 bool QCoreApplicationPrivate::notify_helper(QObject *receiver, QEvent * event)
 {
     // send to all application event filters (only does anything in the main thread)
-    if (QCoreApplication::self->d_func()->sendThroughApplicationEventFilters(receiver, event))
+    if (QCoreApplication::self
+            && receiver->d_func()->threadData->thread == mainThread()
+            && QCoreApplication::self->d_func()->sendThroughApplicationEventFilters(receiver, event))
         return true;
     // send to all receiver event filters
     if (sendThroughObjectEventFilters(receiver, event))
diff --git a/src/corelib/kernel/qcoreapplication_p.h b/src/corelib/kernel/qcoreapplication_p.h
index 5fed850c2b..21f59d8197 100644
--- a/src/corelib/kernel/qcoreapplication_p.h
+++ b/src/corelib/kernel/qcoreapplication_p.h
@@ -107,6 +107,8 @@ public:
 
     static QThread *theMainThread;
     static QThread *mainThread();
+    static bool threadRequiresCoreApplication();
+
     static void sendPostedEvents(QObject *receiver, int event_type, QThreadData *data);
 
     static void checkReceiverThread(QObject *receiver);
diff --git a/src/corelib/kernel/qeventloop.cpp b/src/corelib/kernel/qeventloop.cpp
index 1723db0ab9..dca25ce968 100644
--- a/src/corelib/kernel/qeventloop.cpp
+++ b/src/corelib/kernel/qeventloop.cpp
@@ -93,7 +93,7 @@ QEventLoop::QEventLoop(QObject *parent)
     : QObject(*new QEventLoopPrivate, parent)
 {
     Q_D(QEventLoop);
-    if (!QCoreApplication::instance()) {
+    if (!QCoreApplication::instance() && QCoreApplicationPrivate::threadRequiresCoreApplication()) {
         qWarning("QEventLoop: Cannot be used without QApplication");
     } else if (!d->threadData->eventDispatcher.load()) {
         QThreadPrivate::createEventDispatcher(d->threadData);
diff --git a/src/corelib/thread/qthread.cpp b/src/corelib/thread/qthread.cpp
index 0c009db930..590479d68c 100644
--- a/src/corelib/thread/qthread.cpp
+++ b/src/corelib/thread/qthread.cpp
@@ -50,7 +50,8 @@ QT_BEGIN_NAMESPACE
 
 QThreadData::QThreadData(int initialRefCount)
     : _ref(initialRefCount), loopLevel(0), thread(0), threadId(0),
-      eventDispatcher(0), quitNow(false), canWait(true), isAdopted(false)
+      eventDispatcher(0),
+      quitNow(false), canWait(true), isAdopted(false), requiresCoreApplication(true)
 {
     // fprintf(stderr, "QThreadData %p created\n", this);
 }
@@ -867,4 +868,28 @@ bool QThread::isInterruptionRequested() const
     return d->interruptionRequested;
 }
 
+/*!
+    \class QDaemonThread
+    \since 5.5
+    \brief The QDaemonThread provides a class to manage threads that outlive QCoreApplication
+    \internal
+
+    Note: don't try to deliver events from the started() signal.
+*/
+static void setThreadDoesNotRequireCoreApplication()
+{
+    QThreadData::current()->requiresCoreApplication = false;
+}
+
+QDaemonThread::QDaemonThread(QObject *parent)
+    : QThread(parent)
+{
+    // QThread::started() is emitted from the thread we start
+    connect(this, &QThread::started, setThreadDoesNotRequireCoreApplication);
+}
+
+QDaemonThread::~QDaemonThread()
+{
+}
+
 QT_END_NAMESPACE
diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index 1ecd682ad1..ffefe0b1d1 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -135,6 +135,13 @@ private:
 
 #ifndef QT_NO_THREAD
 
+class Q_CORE_EXPORT QDaemonThread : public QThread
+{
+public:
+    QDaemonThread(QObject *parent = 0);
+    ~QDaemonThread();
+};
+
 class QThreadPrivate : public QObjectPrivate
 {
     Q_DECLARE_PUBLIC(QThread)
@@ -224,7 +231,7 @@ public:
     QThreadData(int initialRefCount = 1);
     ~QThreadData();
 
-    static QThreadData *current(bool createIfNecessary = true);
+    static Q_AUTOTEST_EXPORT QThreadData *current(bool createIfNecessary = true);
     static void clearCurrentThreadData();
     static QThreadData *get2(QThread *thread)
     { Q_ASSERT_X(thread != 0, "QThread", "internal error"); return thread->d_func()->data; }
@@ -278,6 +285,7 @@ public:
     bool quitNow;
     bool canWait;
     bool isAdopted;
+    bool requiresCoreApplication;
 };
 
 class QScopedLoopLevelCounter
diff --git a/src/network/access/qnetworkreplyhttpimpl.cpp b/src/network/access/qnetworkreplyhttpimpl.cpp
index c08648c47b..8c0c098147 100644
--- a/src/network/access/qnetworkreplyhttpimpl.cpp
+++ b/src/network/access/qnetworkreplyhttpimpl.cpp
@@ -49,6 +49,8 @@
 #include "qthread.h"
 #include "QtCore/qcoreapplication.h"
 
+#include <QtCore/private/qthread_p.h>
+
 #include "qnetworkcookiejar.h"
 
 #ifndef QT_NO_HTTP
diff --git a/src/network/bearer/qnetworkconfigmanager_p.cpp b/src/network/bearer/qnetworkconfigmanager_p.cpp
index c1e837de7b..78d4970ca1 100644
--- a/src/network/bearer/qnetworkconfigmanager_p.cpp
+++ b/src/network/bearer/qnetworkconfigmanager_p.cpp
@@ -41,6 +41,7 @@
 #include <QtCore/qstringlist.h>
 #include <QtCore/qthread.h>
 #include <QtCore/private/qcoreapplication_p.h>
+#include <QtCore/private/qthread_p.h>
 
 #ifndef QT_NO_BEARERMANAGEMENT
 
@@ -61,7 +62,7 @@ QNetworkConfigurationManagerPrivate::QNetworkConfigurationManagerPrivate()
 void QNetworkConfigurationManagerPrivate::initialize()
 {
     //Two stage construction, because we only want to do this heavyweight work for the winner of the Q_GLOBAL_STATIC race.
-    bearerThread = new QThread();
+    bearerThread = new QDaemonThread();
     bearerThread->setObjectName(QStringLiteral("Qt bearer thread"));
 
     bearerThread->moveToThread(QCoreApplicationPrivate::mainThread()); // because cleanup() is called in main thread context.
diff --git a/src/platformsupport/input/evdevtablet/qevdevtablet.cpp b/src/platformsupport/input/evdevtablet/qevdevtablet.cpp
index c59f0f390a..c6f952c64d 100644
--- a/src/platformsupport/input/evdevtablet/qevdevtablet.cpp
+++ b/src/platformsupport/input/evdevtablet/qevdevtablet.cpp
@@ -292,7 +292,7 @@ void QEvdevTabletHandler::readData()
 
 
 QEvdevTabletHandlerThread::QEvdevTabletHandlerThread(const QString &spec, QObject *parent)
-    : QThread(parent), m_spec(spec), m_handler(0)
+    : QDaemonThread(parent), m_spec(spec), m_handler(0)
 {
     start();
 }
diff --git a/src/platformsupport/input/evdevtablet/qevdevtablet_p.h b/src/platformsupport/input/evdevtablet/qevdevtablet_p.h
index f9682290d9..f546f9a88a 100644
--- a/src/platformsupport/input/evdevtablet/qevdevtablet_p.h
+++ b/src/platformsupport/input/evdevtablet/qevdevtablet_p.h
@@ -48,6 +48,7 @@
 #include <QObject>
 #include <QString>
 #include <QThread>
+#include <QtCore/private/qthread_p.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -68,7 +69,7 @@ private:
     QEvdevTabletData *d;
 };
 
-class QEvdevTabletHandlerThread : public QThread
+class QEvdevTabletHandlerThread : public QDaemonThread
 {
 public:
     explicit QEvdevTabletHandlerThread(const QString &spec, QObject *parent = 0);
diff --git a/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp b/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
index 1556be5cc1..1ca95074b9 100644
--- a/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
+++ b/src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp
@@ -642,7 +642,7 @@ void QEvdevTouchScreenData::reportPoints()
 
 
 QEvdevTouchScreenHandlerThread::QEvdevTouchScreenHandlerThread(const QString &device, const QString &spec, QObject *parent)
-    : QThread(parent), m_device(device), m_spec(spec), m_handler(0)
+    : QDaemonThread(parent), m_device(device), m_spec(spec), m_handler(0)
 {
     start();
 }
diff --git a/src/platformsupport/input/evdevtouch/qevdevtouchhandler_p.h b/src/platformsupport/input/evdevtouch/qevdevtouchhandler_p.h
index a6d3a860f5..8e7dfe59bb 100644
--- a/src/platformsupport/input/evdevtouch/qevdevtouchhandler_p.h
+++ b/src/platformsupport/input/evdevtouch/qevdevtouchhandler_p.h
@@ -49,6 +49,7 @@
 #include <QString>
 #include <QList>
 #include <QThread>
+#include <QtCore/private/qthread_p.h>
 #include <qpa/qwindowsysteminterface.h>
 
 #if !defined(QT_NO_MTDEV)
@@ -80,7 +81,7 @@ private:
 #endif
 };
 
-class QEvdevTouchScreenHandlerThread : public QThread
+class QEvdevTouchScreenHandlerThread : public QDaemonThread
 {
 public:
     explicit QEvdevTouchScreenHandlerThread(const QString &device, const QString &spec, QObject *parent = 0);
diff --git a/src/widgets/kernel/qapplication.cpp b/src/widgets/kernel/qapplication.cpp
index 504932dc53..f82fac836a 100644
--- a/src/widgets/kernel/qapplication.cpp
+++ b/src/widgets/kernel/qapplication.cpp
@@ -3688,7 +3688,9 @@ bool QApplication::notify(QObject *receiver, QEvent *e)
 bool QApplicationPrivate::notify_helper(QObject *receiver, QEvent * e)
 {
     // send to all application event filters
-    if (sendThroughApplicationEventFilters(receiver, e))
+    if (threadRequiresCoreApplication()
+        && receiver->d_func()->threadData->thread == mainThread()
+        && sendThroughApplicationEventFilters(receiver, e))
         return true;
 
     if (receiver->isWidgetType()) {