[PATCH v2 1/1] mfmediaengine: Don't send event notify when engine is shutdown.

[Yuxuan Shui]

From: Yuxuan Shui

I've also tried saving a cancel cookie from `BeginCreateObject*` and using it to cancel the
operation in engine shutdown. However there are 2 problems:

1. Callback might still get called after `CancelObjectCreation`. Microsoft's
     [own documentation](https://learn.microsoft.com/en-us/windows/win32/api/mfidl/nf-mfidl-imfsource...)
     says as much:
       > Because these methods are asynchronous, however, they might be completed before the
       > operation can be canceled. Therefore, your callback might still be invoked after you
       > call this method.
  2. Our implementations of `BeginCreateObject*` are not cancellable. They call either
     `MFPutWorkItem` or `IMFByteStream_BeginRead`, neight of which provides cancellation.
     (and our `CancelObjectCreation` doesn't actually work. AsyncResult objects aren't added to
     `handler->results` list until they are completed, which means any attempts to cancel an
     yet-to-be-completed object creation will always fail with `MF_E_UNEXPECTED`)
---
 dlls/mfmediaengine/main.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/dlls/mfmediaengine/main.c b/dlls/mfmediaengine/main.c
index 5a63974967d..65686e60f94 100644
--- a/dlls/mfmediaengine/main.c
+++ b/dlls/mfmediaengine/main.c
@@ -1373,6 +1373,14 @@ static HRESULT WINAPI media_engine_load_handler_Invoke(IMFAsyncCallback *iface,
     if (FAILED(hr))
         WARN("Failed to create source object, hr %#lx.\n", hr);

+    if (engine->flags & FLAGS_ENGINE_SHUT_DOWN)
+    {
+        LeaveCriticalSection(&engine->cs);
+        TRACE("Engine is shut down, stopping...\n");
+        IUnknown_Release(object);
+        return S_OK;
+    }
+
     if (object)
     {
         if (SUCCEEDED(hr = IUnknown_QueryInterface(object, &IID_IMFMediaSource, (void **)&source)))