| /* |
| * Copyright 2020 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 <ui/DisplayId.h> |
| |
| #include <limits> |
| #include <optional> |
| #include <random> |
| #include <unordered_set> |
| |
| #include <log/log.h> |
| |
| namespace android { |
| |
| template <typename T> |
| class DisplayIdGenerator { |
| public: |
| virtual std::optional<T> nextId() = 0; |
| virtual void markUnused(T id) = 0; |
| |
| protected: |
| ~DisplayIdGenerator() {} |
| }; |
| |
| template <typename T> |
| class RandomDisplayIdGenerator final : public DisplayIdGenerator<T> { |
| public: |
| explicit RandomDisplayIdGenerator(size_t maxIdsCount = std::numeric_limits<size_t>::max()) |
| : mMaxIdsCount(maxIdsCount) {} |
| |
| std::optional<T> nextId() override { |
| if (mUsedIds.size() >= mMaxIdsCount) { |
| return std::nullopt; |
| } |
| |
| constexpr int kMaxAttempts = 1000; |
| |
| for (int attempts = 0; attempts < kMaxAttempts; attempts++) { |
| const auto baseId = mDistribution(mGenerator); |
| const T id(baseId); |
| if (mUsedIds.count(id) == 0) { |
| mUsedIds.insert(id); |
| return id; |
| } |
| } |
| |
| LOG_ALWAYS_FATAL("Couldn't generate ID after %d attempts", kMaxAttempts); |
| } |
| |
| void markUnused(T id) override { mUsedIds.erase(id); } |
| |
| private: |
| const size_t mMaxIdsCount; |
| |
| std::unordered_set<T> mUsedIds; |
| std::default_random_engine mGenerator{std::random_device()()}; |
| std::uniform_int_distribution<typename T::BaseId> mDistribution; |
| }; |
| |
| } // namespace android |