tdf#149261 sdext: fix crash on starting the presenter console for the 2nd time

This started with commit 3f768cddd28a2f04eb1ffa30bed4474deb6fbfc4
(framework: avoid re-creating protocol handler instances all the time,
2022-05-02). In case there are 2 monitors, then one monitor shows the
slideshow, the other shows the presenter console. The presenter
console's protocol handler in
sdext::presenter::PresenterProtocolHandler::Dispatch::Dispatch() has
mpPresenterController->GetWindowManager() as an empty reference on the
2nd time the presentation starts.

The above commit started to cache protocol handler instances at a frame
level for performance reasons, and this is meant to be safe in general,
but the presenter console's window manager is re-created between
slideshow runs, so it depends on framework/ code to re-create the
protocol handler all the time, which is problematic here.

Fix the problem by introducing a framework::CacheInfo interface that
allows protocol handler implementations to signal if they want to avoid
being cached.

This should be good enough for now, but if later it turns out that there
are too many broken protocol handlers out there, then we can consider
flipping the default and only cache handlers which explicitly opt in for
this behavior. This is not done in this commit.

Change-Id: Ic159813b1b339540bc8c4e780c4d6d7d2d4d2445
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/135020
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

3 files changed, 23 insertions, 1 deletions

diff --git a/framework/source/dispatch/dispatchprovider.cxx b/framework/source/dispatch/dispatchprovider.cxx
index bcfa07bb333a..c16a0085a0a5 100644
--- a/framework/source/dispatch/dispatchprovider.cxx
+++ b/framework/source/dispatch/dispatchprovider.cxx
@@ -36,6 +36,7 @@
 #include <rtl/ustring.hxx>
 #include <vcl/svapp.hxx>
 #include <sal/log.hxx>
+#include <framework/dispatchhelper.hxx>
 
 namespace framework{
 
@@ -451,7 +452,13 @@ css::uno::Reference< css::frame::XDispatch > DispatchProvider::implts_searchProt
                         css::uno::Reference<css::lang::XMultiServiceFactory>(m_xContext->getServiceManager(), css::uno::UNO_QUERY_THROW)
                           ->createInstance(aHandler.m_sUNOName),
                         css::uno::UNO_QUERY);
-                    m_aProtocolHandlers.emplace(aHandler.m_sUNOName, xHandler);
+
+                    // Check if the handler explicitly requested to avoid caching.
+                    auto pCacheInfo = dynamic_cast<framework::CacheInfo*>(xHandler.get());
+                    if (!pCacheInfo || pCacheInfo->IsCachingAllowed())
+                    {
+                        m_aProtocolHandlers.emplace(aHandler.m_sUNOName, xHandler);
+                    }
                 }
                 else
                 {
diff --git a/include/framework/dispatchhelper.hxx b/include/framework/dispatchhelper.hxx
index 7c89a2d79aac..1595e2a3cea2 100644
--- a/include/framework/dispatchhelper.hxx
+++ b/include/framework/dispatchhelper.hxx
@@ -104,6 +104,16 @@ public:
     // XEventListener
     virtual void SAL_CALL disposing(const css::lang::EventObject& aEvent) override;
 };
+
+/// Interface that allows a protocol handler implementation to opt out from framework caching.
+class SAL_NO_VTABLE SAL_DLLPUBLIC_RTTI CacheInfo
+{
+public:
+    virtual bool IsCachingAllowed() const = 0;
+
+protected:
+    ~CacheInfo() noexcept = default;
+};
 }
 
 #endif
diff --git a/sdext/source/presenter/PresenterProtocolHandler.hxx b/sdext/source/presenter/PresenterProtocolHandler.hxx
index 3a5e33f3b8a6..eaced08d9e6a 100644
--- a/sdext/source/presenter/PresenterProtocolHandler.hxx
+++ b/sdext/source/presenter/PresenterProtocolHandler.hxx
@@ -27,6 +27,7 @@
 #include <com/sun/star/lang/XInitialization.hpp>
 #include <com/sun/star/lang/XServiceInfo.hpp>
 #include <rtl/ref.hxx>
+#include <framework/dispatchhelper.hxx>
 
 namespace sdext::presenter {
 
@@ -40,6 +41,7 @@ class PresenterController;
 
 class PresenterProtocolHandler
     : protected ::cppu::BaseMutex,
+      public framework::CacheInfo,
       public PresenterProtocolHandlerInterfaceBase
 {
 public:
@@ -71,6 +73,9 @@ public:
         queryDispatches(
             const css::uno::Sequence< css::frame::DispatchDescriptor>& rDescriptors) override;
 
+    /// See framework::CacheInfo::IsCachingAllowed().
+    bool IsCachingAllowed() const override { return false; }
+
 private:
     class Dispatch;
     ::rtl::Reference<PresenterController> mpPresenterController;