/*
 * Copyright (C) 2023 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.
 */

#include "app_process.h"

#include <pthread.h>

#include <condition_variable>
#include <mutex>

#include "berberis/base/forever_alloc.h"

namespace berberis {

namespace {

class AppProcess {
 public:
  static AppProcess* GetInstance() {
    static auto* g_app_process = NewForever<AppProcess>();
    return g_app_process;
  }

  void PostInit() {
    {
      std::lock_guard<std::mutex> guard(mutex_);
      initialized_ = true;
    }
    cv_.notify_all();

    // Expect this call to occur on the main guest thread, after app
    // initialization is done. Force exit since keeping the thread in the
    // background might confuse an app that expects to be single-threaded.
    // Specifically, this scenario happens when guest code is executed in
    // app-zygote before forking children (b/146904103).
    //
    // Other threads may use main thread's stack to access argc/argv/auxvals.
    // We ensure that stack is retained after pthread_exit() by disallowing
    // stack unmap in main guest thread when starting an executable.
    //
    // Note that we cannot just let the thread exit from main(), which would
    // exit the whole process, not just this thread.
    pthread_exit(nullptr);
  }

  void WaitForPostInit() {
    std::unique_lock<std::mutex> lock(mutex_);
    cv_.wait(lock, [this] { return initialized_; });
  }

 private:
  AppProcess() = default;
  AppProcess(const AppProcess&) = delete;
  AppProcess& operator=(const AppProcess&) = delete;

  friend AppProcess* NewForever<AppProcess>();

  std::mutex mutex_;
  std::condition_variable cv_;
  bool initialized_ = false;
};

}  // namespace

void AppProcessPostInit() {
  AppProcess::GetInstance()->PostInit();
}

void WaitForAppProcess() {
  AppProcess::GetInstance()->WaitForPostInit();
}

}  // namespace berberis