/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef FORKSERVICE_CHILD_H_
#define FORKSERVICE_CHILD_H_

#include "base/process_util.h"
#include "mozilla/GeckoArgs.h"
#include "nsIObserver.h"
#include "nsString.h"
#include "mozilla/ipc/MiniTransceiver.h"
#include "mozilla/ipc/LaunchError.h"
#include "mozilla/Mutex.h"
#include "mozilla/RefPtr.h"
#include "mozilla/Result.h"
#include "mozilla/StaticMutex.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/ThreadSafety.h"

#include <sys/types.h>
#include <poll.h>

namespace mozilla {
namespace ipc {

class GeckoChildProcessHost;

/**
 * This is the interface to the fork server.
 *
 * When the chrome process calls |ForkServiceChild| to create a new
 * process, this class send a message to the fork server through a
 * pipe and get the PID of the new process from the reply.
 */
class ForkServiceChild final {
 public:
  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ForkServiceChild)
  /**
   * Ask the fork server to create a new process with given parameters.
   *
   * \param aArgs arguments with file attachments used in the content process.
   * \param aOptions other options which will be used to create the process.
   *                 Not all launch options are supported.
   * \param aPid returns the PID of the content
   * process created. \return true if success.
   */
  Result<Ok, LaunchError> SendForkNewSubprocess(
      geckoargs::ChildProcessArgs&& aArgs, base::LaunchOptions&& aOptions,
      pid_t* aPid) MOZ_EXCLUDES(mMutex);

  /**
   * Contains a status value as from waitpid (for use with macros
   * like WIFEXITED).
   */
  struct ProcStatus {
    int status;
  };

  /**
   * Ask the fork server to call waitpid on a child process.
   *
   * \param aPid The process ID of the child process.
   * \param aBlock Whether to block until the child process exits;
   *               use with caution.
   *
   * \return Ok(status) if the process exited; Err(0) if the process
   *         is still running; and Err(errno) if there was an error.
   */
  Result<ProcStatus, int> SendWaitPid(pid_t aPid, bool aBlock);

  /**
   * Create a fork server process and the singleton of this class.
   *
   * This function uses |GeckoChildProcessHost| to launch the fork
   * server, getting the fd of a pipe/socket to the fork server from
   * it's |IPC::Channel|.
   */
  static void StartForkServer();
  static void StopForkServer();

  /**
   * Return the singleton.  May return nullptr if the fork server is
   * not running or in the process of being restarted.
   */
  static RefPtr<ForkServiceChild> Get();

  /**
   * Returns whether the fork server was ever active.  Thread-safe.
   */
  static bool WasUsed() { return sForkServiceUsed; }

 private:
  ForkServiceChild(int aFd, GeckoChildProcessHost* aProcess);
  ~ForkServiceChild();

  void OnError() MOZ_REQUIRES(mMutex);

  static StaticMutex sMutex;
  static StaticRefPtr<ForkServiceChild> sSingleton MOZ_GUARDED_BY(sMutex);
  static Atomic<bool> sForkServiceUsed;
  Mutex mMutex;
  UniquePtr<MiniTransceiver> mTcver MOZ_GUARDED_BY(mMutex);
  bool mFailed MOZ_GUARDED_BY(mMutex);  // crashed or disconnected.
  // mProcess is accessed only by the dtor so should be inherently
  // thread-safe
  GeckoChildProcessHost* mProcess;
};

/**
 * Start a fork server at |xpcom-startup| from the chrome process.
 */
class ForkServerLauncher final : public nsIObserver {
 public:
  NS_DECL_ISUPPORTS
  NS_DECL_NSIOBSERVER

  ForkServerLauncher();
  static already_AddRefed<ForkServerLauncher> Create();

 private:
  friend class ForkServiceChild;
  ~ForkServerLauncher() = default;

  static void RestartForkServer();

  static bool sHaveStartedClient;
  static StaticRefPtr<ForkServerLauncher> sSingleton;
};

}  // namespace ipc
}  // namespace mozilla

#endif /* FORKSERVICE_CHILD_H_ */