Android A11Y: Only access the main thread when it is not blocked

When the qtMainLoopThread calls QSGThreadedRenderLoop::polishAndSync(),
it waits for the QSGRenderThread.

In the QSGRenderThread, QAndroidPlatformOpenGLWindow::eglSurface()
calls QtAndroid::createSurface() and waits for the "android main
thread" to return a valid surface.
When the "android main thread" now calls "runInObjectContext" (e.g. by
calling QtAndroidAccessibility::childIdListForAccessibleObject()) it
waits for the qtMainLoopThread and the program is stuck in a deadlock.

To prevent this, we protect all BlockedQueuedConnection from the
"android main thread" to the qtMainLoopThread by acquiring the
AndroidDeadlockProtector.
When QAndroidPlatformOpenGLWindow::eglSurface() already acquired the
AndroidDeadlockProtector we abort the current A11y call with an emtpy
or default value.

Note: b8a95275440b8a143ee648466fd8b5401ee1e839 already tried to fix
this by checking "getSurfaceCount() != 0", but there are situations,
where a new surface is being created while an old surface is still
present.

Task-number: QTBUG-105958
Pick-to: 6.5 6.4 6.3 6.2 5.15
Change-Id: Ie40e8654c99aace9e69b0b8412952fa22c89f071
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>

1 files changed, 9 insertions, 0 deletions

diff --git a/src/plugins/platforms/android/androidjniaccessibility.cpp b/src/plugins/platforms/android/androidjniaccessibility.cpp
index 3067cb178a..8990289dc4 100644
--- a/src/plugins/platforms/android/androidjniaccessibility.cpp
+++ b/src/plugins/platforms/android/androidjniaccessibility.cpp
@@ -1,6 +1,7 @@
 // Copyright (C) 2021 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
+#include "androiddeadlockprotector.h"
 #include "androidjniaccessibility.h"
 #include "androidjnimain.h"
 #include "qandroidplatformintegration.h"
@@ -61,6 +62,14 @@ namespace QtAndroidAccessibility
     template <typename Func, typename Ret>
     void runInObjectContext(QObject *context, Func &&func, Ret *retVal)
     {
+        AndroidDeadlockProtector protector;
+        if (!protector.acquire()) {
+            __android_log_print(ANDROID_LOG_WARN, m_qtTag,
+                                "Could not run accessibility call in object context, accessing "
+                                "main thread could lead to deadlock");
+            return;
+        }
+
         if (!QtAndroid::blockEventLoopsWhenSuspended()
             || QGuiApplication::applicationState() != Qt::ApplicationSuspended) {
             QMetaObject::invokeMethod(context, func, Qt::BlockingQueuedConnection, retVal);