119 lines
3.9 KiB
C++
119 lines
3.9 KiB
C++
/*
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* Copyright (C) 2021 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 <atomic>
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#include <condition_variable>
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#include <cstdint>
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#include <functional>
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#include <mutex>
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#include "common/libs/confui/confui.h"
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#include "host/libs/confui/host_utils.h"
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namespace cuttlefish {
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/**
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* mechanism to orchestrate concurrent executions of threads
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* that work for screen connector
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*
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* Within WebRTC service, it tells when it is now in the Android Mode or
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* Confirmation UI mode
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*/
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class HostModeCtrl {
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public:
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enum class ModeType : std::uint8_t { kAndroidMode = 55, kConfUI_Mode = 77 };
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/**
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* The thread that enqueues Android frames will call this to wait until
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* the mode is kAndroidMode
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*
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* Logically, using atomic_mode_ alone is not sufficient. Using mutex alone
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* is logically complete but slow.
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*
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* Note that most of the time, the mode is kAndroidMode. Also, note that
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* this method is called at every single frame.
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*
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* As an optimization, we check atomic_mode_ first. If failed, we wait for
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* kAndroidMode with mutex-based lock
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*
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* The actual synchronization is not at the and_mode_cv_.wait line but at
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* this line:
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* if (atomic_mode_ == ModeType::kAndroidMode) {
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*
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* This trick reduces the flag checking delays by 70+% on a Gentoo based
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* amd64 desktop, with Linux 5.10
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*/
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void WaitAndroidMode() {
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< "checking atomic Android mode";
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if (atomic_mode_ == ModeType::kAndroidMode) {
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< "returns as it is already Android mode";
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return;
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}
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auto check = [this]() -> bool {
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return atomic_mode_ == ModeType::kAndroidMode;
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};
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std::unique_lock<std::mutex> lock(mode_mtx_);
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and_mode_cv_.wait(lock, check);
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< "awakes from cond var waiting for Android mode";
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}
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void SetMode(const ModeType mode) {
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< " tries to acquire the lock in SetMode";
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std::lock_guard<std::mutex> lock(mode_mtx_);
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< " acquired the lock in SetMode";
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atomic_mode_ = mode;
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if (atomic_mode_ == ModeType::kAndroidMode) {
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< " signals kAndroidMode in SetMode";
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and_mode_cv_.notify_all();
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return;
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}
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ConfUiLog(DEBUG) << cuttlefish::confui::thread::GetName()
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<< "signals kConfUI_Mode in SetMode";
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confui_mode_cv_.notify_all();
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}
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auto GetMode() {
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ModeType ret_val = atomic_mode_;
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return ret_val;
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}
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auto IsConfirmatioUiMode() {
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return (atomic_mode_ == ModeType::kConfUI_Mode);
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}
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auto IsAndroidMode() { return (atomic_mode_ == ModeType::kAndroidMode); }
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static HostModeCtrl& Get() {
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static HostModeCtrl host_mode_controller;
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return host_mode_controller;
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}
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private:
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HostModeCtrl() : atomic_mode_(ModeType::kAndroidMode) {}
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std::mutex mode_mtx_;
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std::condition_variable and_mode_cv_;
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std::condition_variable confui_mode_cv_;
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std::atomic<ModeType> atomic_mode_;
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};
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} // end of namespace cuttlefish
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