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/*
* 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
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