subprocess.h

// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UPDATE_ENGINE_SUBPROCESS_H_
#define UPDATE_ENGINE_SUBPROCESS_H_

#include <glib.h>

#include <map>
#include <memory>
#include <string>
#include <vector>

#include <base/logging.h>
#include <base/macros.h>
#include <chromeos/message_loops/message_loop.h>
#include <gtest/gtest_prod.h>  // for FRIEND_TEST

// The Subprocess class is a singleton. It's used to spawn off a subprocess
// and get notified when the subprocess exits. The result of Exec() can
// be saved and used to cancel the callback request and kill your process. If
// you know you won't call KillExec(), you may safely lose the return value
// from Exec().

namespace chromeos_update_engine {

class Subprocess {
 public:
  typedef void(*ExecCallback)(int return_code,
                              const std::string& output,
                              void *p);

  static void Init() {
    CHECK(!subprocess_singleton_);
    subprocess_singleton_ = new Subprocess;
  }

  // Returns a tag > 0 on success.
  uint32_t Exec(const std::vector<std::string>& cmd,
                ExecCallback callback,
                void* p);
  uint32_t ExecFlags(const std::vector<std::string>& cmd,
                     GSpawnFlags flags,
                     bool redirect_stderr_to_stdout,
                     ExecCallback callback,
                     void* p);

  // Kills the running process with SIGTERM and ignores the callback.
  void KillExec(uint32_t tag);

  // Executes a command synchronously. Returns true on success. If |stdout| is
  // non-null, the process output is stored in it, otherwise the output is
  // logged. Note that stderr is redirected to stdout.
  static bool SynchronousExecFlags(const std::vector<std::string>& cmd,
                                   GSpawnFlags flags,
                                   int* return_code,
                                   std::string* stdout);
  static bool SynchronousExec(const std::vector<std::string>& cmd,
                              int* return_code,
                              std::string* stdout);

  // Gets the one instance.
  static Subprocess& Get() {
    return *subprocess_singleton_;
  }

  // Returns true iff there is at least one subprocess we're waiting on.
  bool SubprocessInFlight();

 private:
  FRIEND_TEST(SubprocessTest, CancelTest);

  struct SubprocessRecord {
    SubprocessRecord() = default;

    uint32_t tag{0};
    chromeos::MessageLoop::TaskId task_id{chromeos::MessageLoop::kTaskIdNull};

    ExecCallback callback{nullptr};
    void* callback_data{nullptr};

    GPid pid;

    int stdout_fd{-1};
    std::string stdout;
  };

  Subprocess() {}

  // Callback for when any subprocess terminates. This calls the user
  // requested callback.
  static void GChildExitedCallback(GPid pid, gint status, gpointer data);

  // Callback which runs in the child before exec to redirect stderr onto
  // stdout.
  static void GRedirectStderrToStdout(gpointer user_data);

  // Callback which runs whenever there is input available on the subprocess
  // stdout pipe.
  static void OnStdoutReady(SubprocessRecord* record);

  // The global instance.
  static Subprocess* subprocess_singleton_;

  // A map from the asynchronous subprocess tag (see Exec) to the subprocess
  // record structure for all active asynchronous subprocesses.
  std::map<uint32_t, std::shared_ptr<SubprocessRecord>> subprocess_records_;

  DISALLOW_COPY_AND_ASSIGN(Subprocess);
};

}  // namespace chromeos_update_engine

#endif  // UPDATE_ENGINE_SUBPROCESS_H_