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/*
* Copyright (C) 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 <sys/system_properties.h>
#include <atomic>
#include <condition_variable>
#include <functional>
#include <mutex>
#include <string>
#include <unordered_map>
using PropertyMonitorCallback = bool(std::string value);
struct PropertyMonitorData {
std::function<PropertyMonitorCallback> callback;
const prop_info* prop_info;
uint32_t serial;
};
// This class is thread-unsafe: all operations must be guarded by mutexes if they can occur on
// different threads.
struct PropertyMonitor {
PropertyMonitor() = default;
~PropertyMonitor() = default;
// Register a callback on a specified property, and immediately invoke it on the current value.
// If the property is not defined, the callback will be invoked with the empty string.
//
// Only one callback can be registered on a property at once: subsequent registrations will
// delete the original callback.
void Add(std::string property, std::function<PropertyMonitorCallback> callback);
// Run the PropertyMonitor indefinitely.
//
// This will run until a callback returns false. If a callback returns false, this does not
// return immediately: it will run the other callbacks for changed properties first.
void Run();
private:
std::unordered_map<std::string, PropertyMonitorData> properties_;
uint32_t last_serial_ = 0;
};
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