From b3b95670b2f7e43cfe49fa90f2dffa74b82c160f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Morten=20Johan=20S=C3=B8rvig?= <morten.sorvig@qt.io>
Date: Wed, 9 Dec 2020 16:31:41 +0100
Subject: [PATCH] Call QEventDispatcher::startingUp() on thread start

...instead of during createEventDispatcher().

This way, startingUp() will be called [on the thread
being started] also for custom event dispatchers installed
with QThread::setEventDispatcher().

This prevents crashes when installing event dispatches which
expects that startingUp() will be called.

Crash reproducible with test case from QTBUG-51961.

Change-Id: I71bd696539689d928a61ff9b47d05297cf803b2f
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
---
 src/corelib/thread/qthread.cpp      | 1 -
 src/corelib/thread/qthread_unix.cpp | 1 +
 src/corelib/thread/qthread_win.cpp  | 1 +
 3 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/corelib/thread/qthread.cpp b/src/corelib/thread/qthread.cpp
index 543c491201..3453fd0fc1 100644
--- a/src/corelib/thread/qthread.cpp
+++ b/src/corelib/thread/qthread.cpp
@@ -125,7 +125,6 @@ QAbstractEventDispatcher *QThreadData::createEventDispatcher()
 {
     QAbstractEventDispatcher *ed = QThreadPrivate::createEventDispatcher(this);
     eventDispatcher.storeRelease(ed);
-    ed->startingUp();
     return ed;
 }
 
diff --git a/src/corelib/thread/qthread_unix.cpp b/src/corelib/thread/qthread_unix.cpp
index f4d4914efc..8d2c83d519 100644
--- a/src/corelib/thread/qthread_unix.cpp
+++ b/src/corelib/thread/qthread_unix.cpp
@@ -308,6 +308,7 @@ void *QThreadPrivate::start(void *arg)
         }
 
         data->ensureEventDispatcher();
+        data->eventDispatcher.loadRelaxed()->startingUp();
 
 #if (defined(Q_OS_LINUX) || defined(Q_OS_MAC) || defined(Q_OS_QNX))
         {
diff --git a/src/corelib/thread/qthread_win.cpp b/src/corelib/thread/qthread_win.cpp
index b59a9d1bb4..820ffa1149 100644
--- a/src/corelib/thread/qthread_win.cpp
+++ b/src/corelib/thread/qthread_win.cpp
@@ -312,6 +312,7 @@ unsigned int __stdcall QT_ENSURE_STACK_ALIGNED_FOR_SSE QThreadPrivate::start(voi
     }
 
     data->ensureEventDispatcher();
+    data->eventDispatcher.loadRelaxed()->startingUp();
 
 #if !defined(QT_NO_DEBUG) && defined(Q_CC_MSVC)
     // sets the name of the current thread.