Ensure WebEngineContext::destroy() is called before the destructor

Add a false reference only removed after destroy() is called, so the
tearing down of static objects won't dereference it before the
QApplication is destroyed and the post routines including destroy()
are called.

Also adds a little safety by asserting destroy() has been called
before ~WebEngineContext() and make sure we don't create a new
WebEngineContext() during shut down.

Task-number: QTBUG-54769
Change-Id: I2b1d189f9ebd8da2dc9f322f9bb307a5aa0c6a2f
Reviewed-by: Florian Bruhin <qt-project.org@the-compiler.org>
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/core/web_engine_context.cpp b/src/core/web_engine_context.cpp
index 98fba0897..7d1e5d609 100644
--- a/src/core/web_engine_context.cpp
+++ b/src/core/web_engine_context.cpp
@@ -102,6 +102,7 @@ QT_END_NAMESPACE
 namespace {
 
 scoped_refptr<QtWebEngineCore::WebEngineContext> sContext;
+static bool s_destroyed = false;
 
 void destroyContext()
 {
@@ -110,6 +111,7 @@ void destroyContext()
     // WebEngineContext's pointer is used.
     sContext->destroy();
     sContext = 0;
+    s_destroyed = true;
 }
 
 bool usingANGLE()
@@ -184,18 +186,29 @@ void WebEngineContext::destroy()
     // RenderProcessHostImpl should be destroyed before WebEngineContext since
     // default BrowserContext might be used by the RenderprocessHostImpl's destructor.
     m_browserRunner.reset(0);
+
+    // Drop the false reference.
+    sContext->Release();
 }
 
 WebEngineContext::~WebEngineContext()
 {
+    // WebEngineContext::destroy() must be called before we are deleted
+    Q_ASSERT(!m_globalQObject);
+    Q_ASSERT(!m_devtools);
+    Q_ASSERT(!m_browserRunner);
 }
 
 scoped_refptr<WebEngineContext> WebEngineContext::current()
 {
+    if (s_destroyed)
+        return nullptr;
     if (!sContext.get()) {
         sContext = new WebEngineContext();
         // Make sure that we ramp down Chromium before QApplication destroys its X connection, etc.
         qAddPostRoutine(destroyContext);
+        // Add a false reference so there is no race between unreferencing sContext and a global QApplication.
+        sContext->AddRef();
     }
     return sContext;
 }