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72 lines
2.1 KiB
72 lines
2.1 KiB
/*
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* Copyright 2020 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#pragma once
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#include <ui/DisplayId.h>
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#include <limits>
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#include <optional>
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#include <random>
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#include <unordered_set>
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#include <log/log.h>
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namespace android {
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// Generates pseudo-random IDs of type GpuVirtualDisplayId or HalVirtualDisplayId.
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template <typename Id>
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class DisplayIdGenerator {
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public:
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explicit DisplayIdGenerator(size_t maxIdsCount = std::numeric_limits<size_t>::max())
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: mMaxIdsCount(maxIdsCount) {}
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bool inUse() const { return !mUsedIds.empty(); }
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std::optional<Id> generateId() {
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if (mUsedIds.size() >= mMaxIdsCount) {
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return std::nullopt;
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}
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constexpr int kMaxAttempts = 1000;
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for (int attempts = 0; attempts < kMaxAttempts; attempts++) {
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const Id id{mDistribution(mGenerator)};
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if (mUsedIds.count(id) == 0) {
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mUsedIds.insert(id);
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return id;
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}
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}
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LOG_ALWAYS_FATAL("Couldn't generate ID after %d attempts", kMaxAttempts);
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}
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void releaseId(Id id) { mUsedIds.erase(id); }
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private:
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const size_t mMaxIdsCount;
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std::unordered_set<Id> mUsedIds;
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// Pseudo-random with random seed, in contrast to physical display IDs, which are stable
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// across reboots. The only ISurfaceComposer exposure for these IDs is a restricted API
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// for screencap, so there is little benefit in making them unpredictable.
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std::default_random_engine mGenerator{std::random_device()()};
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std::uniform_int_distribution<typename Id::BaseId> mDistribution;
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};
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} // namespace android
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