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Diffstat (limited to 'services/surfaceflinger/DisplayIdGenerator.h')
-rw-r--r-- | services/surfaceflinger/DisplayIdGenerator.h | 71 |
1 files changed, 71 insertions, 0 deletions
diff --git a/services/surfaceflinger/DisplayIdGenerator.h b/services/surfaceflinger/DisplayIdGenerator.h new file mode 100644 index 0000000000..9791a2504a --- /dev/null +++ b/services/surfaceflinger/DisplayIdGenerator.h @@ -0,0 +1,71 @@ +/* + * 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 { + +// Generates pseudo-random IDs of type GpuVirtualDisplayId or HalVirtualDisplayId. +template <typename Id> +class DisplayIdGenerator { +public: + explicit DisplayIdGenerator(size_t maxIdsCount = std::numeric_limits<size_t>::max()) + : mMaxIdsCount(maxIdsCount) {} + + bool inUse() const { return !mUsedIds.empty(); } + + std::optional<Id> generateId() { + if (mUsedIds.size() >= mMaxIdsCount) { + return std::nullopt; + } + + constexpr int kMaxAttempts = 1000; + + for (int attempts = 0; attempts < kMaxAttempts; attempts++) { + const Id id{mDistribution(mGenerator)}; + if (mUsedIds.count(id) == 0) { + mUsedIds.insert(id); + return id; + } + } + + LOG_ALWAYS_FATAL("Couldn't generate ID after %d attempts", kMaxAttempts); + } + + void releaseId(Id id) { mUsedIds.erase(id); } + +private: + const size_t mMaxIdsCount; + + std::unordered_set<Id> mUsedIds; + + // Pseudo-random with random seed, in contrast to physical display IDs, which are stable + // across reboots. The only ISurfaceComposer exposure for these IDs is a restricted API + // for screencap, so there is little benefit in making them unpredictable. + std::default_random_engine mGenerator{std::random_device()()}; + std::uniform_int_distribution<typename Id::BaseId> mDistribution; +}; + +} // namespace android |