[1/4][Ozone-Drm] Process display hotplug events sequentially

ui/ozone/platform/drm/host/drm_native_display_delegate.h

Index: ui/ozone/platform/drm/host/drm_native_display_delegate.h
diff --git a/ui/ozone/platform/drm/host/drm_native_display_delegate.h b/ui/ozone/platform/drm/host/drm_native_display_delegate.h
index d28ea68d346763812299f5a8e7237a88f07be747..f6269bcd96db958affcf3e1f60c46d4befe03014 100644
--- a/ui/ozone/platform/drm/host/drm_native_display_delegate.h
+++ b/ui/ozone/platform/drm/host/drm_native_display_delegate.h
@@ -6,13 +6,17 @@
 #define UI_OZONE_PLATFORM_DRM_HOST_NATIVE_DISPLAY_DELEGATE_HOST_H_
 
 #include <map>
+#include <queue>
+#include <set>
 
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_vector.h"
 #include "base/observer_list.h"
 #include "ui/display/types/native_display_delegate.h"
+#include "ui/events/ozone/device/device_event.h"
 #include "ui/events/ozone/device/device_event_observer.h"
 #include "ui/ozone/public/gpu_platform_support_host.h"
 
@@ -76,11 +80,26 @@ class DrmNativeDisplayDelegate : public NativeDisplayDelegate,
   bool OnMessageReceived(const IPC::Message& message) override;
 
  private:
+  struct DisplayEvent {
+    DisplayEvent(DeviceEvent::ActionType action_type,
+                 const base::FilePath& path)
+        : action_type(action_type), path(path) {}
+
+    DeviceEvent::ActionType action_type;
+    base::FilePath path;
+  };
+
   void OnUpdateNativeDisplays(
       const std::vector<DisplaySnapshot_Params>& displays);
   void OnDisplayConfigured(int64_t display_id, bool status);
 
-  void OnNewGraphicsDevice(const base::FilePath& path, base::File file);
+  void ProcessEvent();
+
+  // Called as a result of finishing to process the display hotplug event. These
+  // are responsible for dequing the event and scheduling the next event.
+  void OnAddGraphicsDevice(const base::FilePath& path, base::File file);
+  void OnUpdateGraphicsDevice();
+  void OnRemoveGraphicsDevice(const base::FilePath& path);
 
   void OnHDCPStateReceived(int64_t display_id, bool status, HDCPState state);
   void OnHDCPStateUpdated(int64_t display_id, bool status);
@@ -112,6 +131,18 @@ class DrmNativeDisplayDelegate : public NativeDisplayDelegate,
 
   std::map<int64_t, SetHDCPStateCallback> set_hdcp_state_callback_map_;
 
+  // Used to serialize display event processing. This is done since
+  // opening/closing DRM devices cannot be done on the UI thread and are handled
+  // on a worker thread. Thus, we need to queue events in order to process them
+  // in the correct order.
+  std::queue<DisplayEvent> event_queue_;
+
+  // True if a display event is currently being processed on a worker thread.
+  bool task_pending_;
+
+  // Keeps track of all the active DRM devices.
+  std::set<base::FilePath> drm_devices_;
+
   base::WeakPtrFactory<DrmNativeDisplayDelegate> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DrmNativeDisplayDelegate);