SF: Create a cicular buffer structure to store layer information.
This structure is going to hold information about history of layers. For now,
we keep information about layers inserted and their presentation timestamp.
Every container (unordered_map) holds information about layers presented at a given
frame. At the beginning of frame, we clear the map and add every layer that had an update
at that frame.
We expose a function to increment the counter of the structure, so that can be
incremented each time SurfaceFlinger wakes up.
see go/surface-flinger-scheduler for more info
Test: Adding a unit test for the simple structure.
Bug: 113612090
Change-Id: If120a15b5f9a0883e70b348dc8cca1b2e4f85f5d
diff --git a/services/surfaceflinger/Scheduler/LayerHistory.h b/services/surfaceflinger/Scheduler/LayerHistory.h
new file mode 100644
index 0000000..1a7f9cd
--- /dev/null
+++ b/services/surfaceflinger/Scheduler/LayerHistory.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <array>
+#include <cinttypes>
+#include <cstdint>
+#include <numeric>
+#include <string>
+#include <unordered_map>
+
+#include <utils/Timers.h>
+
+namespace android {
+
+/*
+ * This class represents a circular buffer in which we keep layer history for
+ * the past ARRAY_SIZE frames. Each time, a signal for new frame comes, the counter
+ * gets incremented and includes all the layers that are requested to draw in that
+ * frame.
+ *
+ * Once the buffer reaches the end of the array, it starts overriding the elements
+ * at the beginning of the array.
+ */
+class LayerHistory {
+public:
+ LayerHistory();
+ ~LayerHistory();
+
+ // Method for inserting layers and their requested present time into the ring buffer.
+ // The elements are going to be inserted into an unordered_map at the position of
+ // mCounter.
+ void insert(const std::string layerName, nsecs_t presentTime);
+ // Method for incrementing the current slot in the ring buffer. It also clears the
+ // unordered_map, if it was created previously.
+ void incrementCounter();
+ // Returns unordered_map at the given at index.
+ const std::unordered_map<std::string, nsecs_t>& get(size_t index) const;
+
+private:
+ size_t mCounter = 0;
+ static constexpr size_t ARRAY_SIZE = 30;
+ std::array<std::unordered_map<std::string, nsecs_t>, ARRAY_SIZE> mElements;
+};
+
+} // namespace android
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