1 files changed, 33 insertions, 11 deletions
diff --git a/src/corelib/kernel/qtimer.cpp b/src/corelib/kernel/qtimer.cpp
index 9c074a064f8..5d1a9c7497c 100644
--- a/src/corelib/kernel/qtimer.cpp
+++ b/src/corelib/kernel/qtimer.cpp
@@ -8,6 +8,7 @@
 #include "qabstracteventdispatcher.h"
 #include "qcoreapplication.h"
 #include "qcoreapplication_p.h"
+#include "qdeadlinetimer.h"
 #include "qmetaobject_p.h"
 #include "qobject_p.h"
 #include "qproperty_p.h"
@@ -249,12 +250,14 @@ void QTimer::timerEvent(QTimerEvent *e)
 class QSingleShotTimer : public QObject
 {
     Q_OBJECT
-    int timerId;
+    int timerId = -1;
 public:
     ~QSingleShotTimer();
     QSingleShotTimer(int msec, Qt::TimerType timerType, const QObject *r, const char * m);
     QSingleShotTimer(int msec, Qt::TimerType timerType, const QObject *r, QtPrivate::QSlotObjectBase *slotObj);
 
+    void startTimerForReceiver(int msec, Qt::TimerType timerType, const QObject *receiver);
+
 Q_SIGNALS:
     void timeout();
 protected:
@@ -264,27 +267,20 @@ protected:
 QSingleShotTimer::QSingleShotTimer(int msec, Qt::TimerType timerType, const QObject *r, const char *member)
     : QObject(QAbstractEventDispatcher::instance())
 {
-    timerId = startTimer(std::chrono::milliseconds{msec}, timerType);
     connect(this, SIGNAL(timeout()), r, member);
+
+    startTimerForReceiver(msec, timerType, r);
 }
 
 QSingleShotTimer::QSingleShotTimer(int msec, Qt::TimerType timerType, const QObject *r, QtPrivate::QSlotObjectBase *slotObj)
     : QObject(QAbstractEventDispatcher::instance())
 {
-    timerId = startTimer(std::chrono::milliseconds{msec}, timerType);
-
     int signal_index = QMetaObjectPrivate::signalOffset(&staticMetaObject);
     Q_ASSERT(QMetaObjectPrivate::signal(&staticMetaObject, signal_index).name() == "timeout");
     QObjectPrivate::connectImpl(this, signal_index, r ? r : this, nullptr, slotObj,
                                 Qt::AutoConnection, nullptr, &staticMetaObject);
 
-    // ### Why is this here? Why doesn't the case above need it?
-    if (r && thread() != r->thread()) {
-        // Avoid leaking the QSingleShotTimer instance in case the application exits before the timer fires
-        connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this, &QObject::deleteLater);
-        setParent(nullptr);
-        moveToThread(r->thread());
-    }
+    startTimerForReceiver(msec, timerType, r);
 }
 
 QSingleShotTimer::~QSingleShotTimer()
@@ -293,6 +289,32 @@ QSingleShotTimer::~QSingleShotTimer()
         killTimer(timerId);
 }
 
+/*
+    Move the timer, and the dispatching and handling of the timer event, into
+    the same thread as where it will be handled, so that it fires reliably even
+    if the thread that set up the timer is busy.
+*/
+void QSingleShotTimer::startTimerForReceiver(int msec, Qt::TimerType timerType, const QObject *receiver)
+{
+    if (receiver && receiver->thread() != thread()) {
+        // Avoid leaking the QSingleShotTimer instance in case the application exits before the timer fires
+        connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this, &QObject::deleteLater);
+        setParent(nullptr);
+        moveToThread(receiver->thread());
+
+        QDeadlineTimer deadline(std::chrono::milliseconds{msec}, timerType);
+        QMetaObject::invokeMethod(this, [=]{
+            if (deadline.hasExpired())
+                emit timeout();
+            else
+                timerId = startTimer(std::chrono::milliseconds{deadline.remainingTime()}, timerType);
+        }, Qt::QueuedConnection);
+    } else {
+        timerId = startTimer(std::chrono::milliseconds{msec}, timerType);
+    }
+}
+
+
 void QSingleShotTimer::timerEvent(QTimerEvent *)
 {
     // need to kill the timer _before_ we emit timeout() in case the