vk_resource_manager: Implement VKFenceWatch

A fence watch is used to keep track of the usage of a fence and protect
a resource or set of resources without having to inherit from their
handlers.

src/video_core/renderer_vulkan/vk_resource_manager.cpp

@@ -3,6 +3,7 @@
 // Refer to the license.txt file included.
 
 #include <algorithm>
+#include "common/assert.h"
 #include "video_core/renderer_vulkan/declarations.h"
 #include "video_core/renderer_vulkan/vk_device.h"
 #include "video_core/renderer_vulkan/vk_resource_manager.h"
@@ -79,4 +80,41 @@ void VKFence::Unprotect(const VKResource* resource) {
     }
 }
 
+VKFenceWatch::VKFenceWatch() = default;
+
+VKFenceWatch::~VKFenceWatch() {
+    if (fence) {
+        fence->Unprotect(this);
+    }
+}
+
+void VKFenceWatch::Wait() {
+    if (!fence) {
+        return;
+    }
+    fence->Wait();
+    fence->Unprotect(this);
+    fence = nullptr;
+}
+
+void VKFenceWatch::Watch(VKFence& new_fence) {
+    Wait();
+    fence = &new_fence;
+    fence->Protect(this);
+}
+
+bool VKFenceWatch::TryWatch(VKFence& new_fence) {
+    if (fence) {
+        return false;
+    }
+    fence = &new_fence;
+    fence->Protect(this);
+    return true;
+}
+
+void VKFenceWatch::OnFenceRemoval(VKFence* signaling_fence) {
+    ASSERT_MSG(signaling_fence == fence, "Removing the wrong fence");
+    fence = nullptr;
+}
+
 } // namespace Vulkan

src/video_core/renderer_vulkan/vk_resource_manager.h

@@ -86,4 +86,34 @@ private:
     bool is_used = false;  ///< The fence has been commited but it has not been checked to be free.
 };
 
+/**
+ * A fence watch is used to keep track of the usage of a fence and protect a resource or set of
+ * resources without having to inherit VKResource from their handlers.
+ */
+class VKFenceWatch final : public VKResource {
+public:
+    explicit VKFenceWatch();
+    ~VKFenceWatch();
+
+    /// Waits for the fence to be released.
+    void Wait();
+
+    /**
+     * Waits for a previous fence and watches a new one.
+     * @param new_fence New fence to wait to.
+     */
+    void Watch(VKFence& new_fence);
+
+    /**
+     * Checks if it's currently being watched and starts watching it if it's available.
+     * @returns True if a watch has started, false if it's being watched.
+     */
+    bool TryWatch(VKFence& new_fence);
+
+    void OnFenceRemoval(VKFence* signaling_fence) override;
+
+private:
+    VKFence* fence{}; ///< Fence watching this resource. nullptr when the watch is free.
+};
+
 } // namespace Vulkan