コード例 #1
0
ファイル: ppo_trainer.py プロジェクト: NicoGrande/habitat-api
class PPOTrainer(BaseRLTrainer):
    r"""Trainer class for PPO algorithm
    Paper: https://arxiv.org/abs/1707.06347.
    """
    supported_tasks = ["Nav-v0"]

    def __init__(self, config=None):
        super().__init__(config)
        self.actor_critic = None
        self.agent = None
        self.envs = None
        if config is not None:
            logger.info(f"config: {config}")

        self._static_encoder = False
        self._encoder = None

    def _setup_actor_critic_agent(self, ppo_cfg: Config) -> None:
        r"""Sets up actor critic and agent for PPO.

        Args:
            ppo_cfg: config node with relevant params

        Returns:
            None
        """
        logger.add_filehandler(self.config.LOG_FILE)

        self.actor_critic = PointNavBaselinePolicy(
            observation_space=self.envs.observation_spaces[0],
            action_space=self.envs.action_spaces[0],
            hidden_size=ppo_cfg.hidden_size,
            goal_sensor_uuid=self.config.TASK_CONFIG.TASK.GOAL_SENSOR_UUID,
        )
        self.actor_critic.to(self.device)

        self.agent = PPO(
            actor_critic=self.actor_critic,
            clip_param=ppo_cfg.clip_param,
            ppo_epoch=ppo_cfg.ppo_epoch,
            num_mini_batch=ppo_cfg.num_mini_batch,
            value_loss_coef=ppo_cfg.value_loss_coef,
            entropy_coef=ppo_cfg.entropy_coef,
            lr=ppo_cfg.lr,
            eps=ppo_cfg.eps,
            max_grad_norm=ppo_cfg.max_grad_norm,
            use_normalized_advantage=ppo_cfg.use_normalized_advantage,
        )

    def save_checkpoint(self,
                        file_name: str,
                        extra_state: Optional[Dict] = None) -> None:
        r"""Save checkpoint with specified name.

        Args:
            file_name: file name for checkpoint

        Returns:
            None
        """
        checkpoint = {
            "state_dict": self.agent.state_dict(),
            "config": self.config,
        }
        if extra_state is not None:
            checkpoint["extra_state"] = extra_state

        torch.save(checkpoint,
                   os.path.join(self.config.CHECKPOINT_FOLDER, file_name))

    def load_checkpoint(self, checkpoint_path: str, *args, **kwargs) -> Dict:
        r"""Load checkpoint of specified path as a dict.

        Args:
            checkpoint_path: path of target checkpoint
            *args: additional positional args
            **kwargs: additional keyword args

        Returns:
            dict containing checkpoint info
        """
        return torch.load(checkpoint_path, *args, **kwargs)

    METRICS_BLACKLIST = {"top_down_map", "collisions.is_collision"}

    @classmethod
    def _extract_scalars_from_info(cls, info: Dict[str,
                                                   Any]) -> Dict[str, float]:
        result = {}
        for k, v in info.items():
            if k in cls.METRICS_BLACKLIST:
                continue

            if isinstance(v, dict):
                result.update({
                    k + "." + subk: subv
                    for subk, subv in cls._extract_scalars_from_info(
                        v).items()
                    if (k + "." + subk) not in cls.METRICS_BLACKLIST
                })
            # Things that are scalar-like will have an np.size of 1.
            # Strings also have an np.size of 1, so explicitly ban those
            elif np.size(v) == 1 and not isinstance(v, str):
                result[k] = float(v)

        return result

    @classmethod
    def _extract_scalars_from_infos(
            cls, infos: List[Dict[str, Any]]) -> Dict[str, List[float]]:

        results = defaultdict(list)
        for i in range(len(infos)):
            for k, v in cls._extract_scalars_from_info(infos[i]).items():
                results[k].append(v)

        return results

    def _collect_rollout_step(self, rollouts, current_episode_reward,
                              running_episode_stats):
        pth_time = 0.0
        env_time = 0.0

        t_sample_action = time.time()
        # sample actions
        with torch.no_grad():
            step_observation = {
                k: v[rollouts.step]
                for k, v in rollouts.observations.items()
            }

            (
                values,
                actions,
                actions_log_probs,
                recurrent_hidden_states,
            ) = self.actor_critic.act(
                step_observation,
                rollouts.recurrent_hidden_states[rollouts.step],
                rollouts.prev_actions[rollouts.step],
                rollouts.masks[rollouts.step],
            )

        pth_time += time.time() - t_sample_action

        t_step_env = time.time()

        outputs = self.envs.step([a[0].item() for a in actions])
        observations, rewards, dones, infos = [list(x) for x in zip(*outputs)]

        env_time += time.time() - t_step_env

        t_update_stats = time.time()
        batch = batch_obs(observations, device=self.device)
        rewards = torch.tensor(rewards,
                               dtype=torch.float,
                               device=current_episode_reward.device)
        rewards = rewards.unsqueeze(1)

        masks = torch.tensor(
            [[0.0] if done else [1.0] for done in dones],
            dtype=torch.float,
            device=current_episode_reward.device,
        )

        current_episode_reward += rewards
        running_episode_stats["reward"] += (1 - masks) * current_episode_reward
        running_episode_stats["count"] += 1 - masks
        for k, v in self._extract_scalars_from_infos(infos).items():
            v = torch.tensor(v,
                             dtype=torch.float,
                             device=current_episode_reward.device).unsqueeze(1)
            if k not in running_episode_stats:
                running_episode_stats[k] = torch.zeros_like(
                    running_episode_stats["count"])

            running_episode_stats[k] += (1 - masks) * v

        current_episode_reward *= masks

        if self._static_encoder:
            with torch.no_grad():
                batch["prev_visual_features"] = step_observation[
                    "visual_features"]
                batch["visual_features"] = self._encoder(batch)

        rollouts.insert(
            batch,
            recurrent_hidden_states,
            actions,
            actions_log_probs,
            values,
            rewards,
            masks,
        )

        pth_time += time.time() - t_update_stats

        return pth_time, env_time, self.envs.num_envs

    def _update_agent(self, ppo_cfg, rollouts):
        t_update_model = time.time()
        with torch.no_grad():
            last_observation = {
                k: v[rollouts.step]
                for k, v in rollouts.observations.items()
            }
            next_value = self.actor_critic.get_value(
                last_observation,
                rollouts.recurrent_hidden_states[rollouts.step],
                rollouts.prev_actions[rollouts.step],
                rollouts.masks[rollouts.step],
            ).detach()

        rollouts.compute_returns(next_value, ppo_cfg.use_gae, ppo_cfg.gamma,
                                 ppo_cfg.tau)

        value_loss, action_loss, dist_entropy, query_loss = self.agent.update(
            rollouts)

        rollouts.after_update()

        return (
            time.time() - t_update_model,
            value_loss,
            action_loss,
            dist_entropy,
            query_loss,
        )

    def train(self) -> None:
        r"""Main method for training PPO.
        Returns:
            None
        """

        self.envs = construct_envs(self.config,
                                   get_env_class(self.config.ENV_NAME))

        ppo_cfg = self.config.RL.PPO
        self.device = (torch.device("cuda", self.config.TORCH_GPU_ID)
                       if torch.cuda.is_available() else torch.device("cpu"))
        if not os.path.isdir(self.config.CHECKPOINT_FOLDER):
            os.makedirs(self.config.CHECKPOINT_FOLDER)
        self._setup_actor_critic_agent(ppo_cfg)
        logger.info("agent number of parameters: {}".format(
            sum(param.numel() for param in self.agent.parameters())))

        rollouts = RolloutStorage(
            ppo_cfg.num_steps,
            self.envs.num_envs,
            self.envs.observation_spaces[0],
            self.envs.action_spaces[0],
            ppo_cfg.hidden_size,
        )
        rollouts.to(self.device)

        observations = self.envs.reset()
        batch = batch_obs(observations, device=self.device)

        for sensor in rollouts.observations:
            rollouts.observations[sensor][0].copy_(batch[sensor])

        # batch and observations may contain shared PyTorch CUDA
        # tensors.  We must explicitly clear them here otherwise
        # they will be kept in memory for the entire duration of training!
        batch = None
        observations = None

        current_episode_reward = torch.zeros(self.envs.num_envs, 1)
        running_episode_stats = dict(
            count=torch.zeros(self.envs.num_envs, 1),
            reward=torch.zeros(self.envs.num_envs, 1),
        )
        window_episode_stats = defaultdict(
            lambda: deque(maxlen=ppo_cfg.reward_window_size))

        t_start = time.time()
        env_time = 0
        pth_time = 0
        count_steps = 0
        count_checkpoints = 0

        lr_scheduler = LambdaLR(
            optimizer=self.agent.optimizer,
            lr_lambda=lambda x: linear_decay(x, self.config.NUM_UPDATES),
        )

        with TensorboardWriter(self.config.TENSORBOARD_DIR,
                               flush_secs=self.flush_secs) as writer:
            for update in range(self.config.NUM_UPDATES):
                if ppo_cfg.use_linear_lr_decay:
                    lr_scheduler.step()

                if ppo_cfg.use_linear_clip_decay:
                    self.agent.clip_param = ppo_cfg.clip_param * linear_decay(
                        update, self.config.NUM_UPDATES)

                for step in range(ppo_cfg.num_steps):
                    (
                        delta_pth_time,
                        delta_env_time,
                        delta_steps,
                    ) = self._collect_rollout_step(rollouts,
                                                   current_episode_reward,
                                                   running_episode_stats)
                    pth_time += delta_pth_time
                    env_time += delta_env_time
                    count_steps += delta_steps

                (
                    delta_pth_time,
                    value_loss,
                    action_loss,
                    dist_entropy,
                ) = self._update_agent(ppo_cfg, rollouts)
                pth_time += delta_pth_time

                for k, v in running_episode_stats.items():
                    window_episode_stats[k].append(v.clone())

                deltas = {
                    k:
                    ((v[-1] -
                      v[0]).sum().item() if len(v) > 1 else v[0].sum().item())
                    for k, v in window_episode_stats.items()
                }
                deltas["count"] = max(deltas["count"], 1.0)

                writer.add_scalar("reward", deltas["reward"] / deltas["count"],
                                  count_steps)

                # Check to see if there are any metrics
                # that haven't been logged yet
                metrics = {
                    k: v / deltas["count"]
                    for k, v in deltas.items() if k not in {"reward", "count"}
                }
                if len(metrics) > 0:
                    writer.add_scalars("metrics", metrics, count_steps)

                losses = [value_loss, action_loss]
                writer.add_scalars(
                    "losses",
                    {k: l
                     for l, k in zip(losses, ["value", "policy"])},
                    count_steps,
                )

                # log stats
                if update > 0 and update % self.config.LOG_INTERVAL == 0:
                    logger.info("update: {}\tfps: {:.3f}\t".format(
                        update, count_steps / (time.time() - t_start)))

                    logger.info(
                        "update: {}\tenv-time: {:.3f}s\tpth-time: {:.3f}s\t"
                        "frames: {}".format(update, env_time, pth_time,
                                            count_steps))

                    logger.info("Average window size: {}  {}".format(
                        len(window_episode_stats["count"]),
                        "  ".join("{}: {:.3f}".format(k, v / deltas["count"])
                                  for k, v in deltas.items() if k != "count"),
                    ))

                # checkpoint model
                if update % self.config.CHECKPOINT_INTERVAL == 0:
                    self.save_checkpoint(f"ckpt.{count_checkpoints}.pth",
                                         dict(step=count_steps))
                    count_checkpoints += 1

            self.envs.close()

    def _eval_checkpoint(
        self,
        checkpoint_path: str,
        writer: TensorboardWriter,
        checkpoint_index: int = 0,
    ) -> None:
        r"""Evaluates a single checkpoint.

        Args:
            checkpoint_path: path of checkpoint
            writer: tensorboard writer object for logging to tensorboard
            checkpoint_index: index of cur checkpoint for logging

        Returns:
            None
        """
        # Map location CPU is almost always better than mapping to a CUDA device.
        ckpt_dict = self.load_checkpoint(checkpoint_path, map_location="cpu")

        if self.config.EVAL.USE_CKPT_CONFIG:
            config = self._setup_eval_config(ckpt_dict["config"])
        else:
            config = self.config.clone()

        ppo_cfg = config.RL.PPO

        config.defrost()
        config.TASK_CONFIG.DATASET.SPLIT = config.EVAL.SPLIT
        config.freeze()

        if len(self.config.VIDEO_OPTION) > 0:
            config.defrost()
            config.TASK_CONFIG.TASK.MEASUREMENTS.append("TOP_DOWN_MAP")
            config.TASK_CONFIG.TASK.MEASUREMENTS.append("COLLISIONS")
            config.freeze()

        logger.info(f"env config: {config}")
        self.envs = construct_envs(config, get_env_class(config.ENV_NAME))
        self._setup_actor_critic_agent(ppo_cfg)
        self.actor_critic.eval()

        if self._static_encoder:
            self._encoder = self.agent.actor_critic.net.visual_encoder

        self.agent.load_state_dict(ckpt_dict["state_dict"])
        self.actor_critic = self.agent.actor_critic

        observations = self.envs.reset()
        batch = batch_obs(observations, device=self.device)

        if self._static_encoder:
            batch["visual_features"] = self._encoder(batch)
            batch["prev_visual_features"] = torch.zeros_like(
                batch["visual_features"])

        current_episode_reward = torch.zeros(self.envs.num_envs,
                                             1,
                                             device=self.device)

        test_recurrent_hidden_states = torch.zeros(
            self.actor_critic.net.num_recurrent_layers,
            self.config.NUM_PROCESSES,
            ppo_cfg.hidden_size,
            device=self.device,
        )
        prev_actions = torch.zeros(self.config.NUM_PROCESSES,
                                   1,
                                   device=self.device,
                                   dtype=torch.long)
        not_done_masks = torch.zeros(self.config.NUM_PROCESSES,
                                     1,
                                     device=self.device)
        stats_episodes = dict()  # dict of dicts that stores stats per episode

        rgb_frames = [[] for _ in range(self.config.NUM_PROCESSES)
                      ]  # type: List[List[np.ndarray]]
        if len(self.config.VIDEO_OPTION) > 0:
            os.makedirs(self.config.VIDEO_DIR, exist_ok=True)

        number_of_eval_episodes = self.config.TEST_EPISODE_COUNT
        if number_of_eval_episodes == -1:
            number_of_eval_episodes = sum(self.envs.number_of_episodes)
        else:
            total_num_eps = sum(self.envs.number_of_episodes)
            if total_num_eps < number_of_eval_episodes:
                logger.warn(
                    f"Config specified {number_of_eval_episodes} eval episodes"
                    ", dataset only has {total_num_eps}.")
                logger.warn(f"Evaluating with {total_num_eps} instead.")
                number_of_eval_episodes = total_num_eps

        pbar = tqdm.tqdm(total=number_of_eval_episodes)
        self.actor_critic.eval()
        while (len(stats_episodes) < number_of_eval_episodes
               and self.envs.num_envs > 0):
            current_episodes = self.envs.current_episodes()

            with torch.no_grad():
                step_batch = batch
                (
                    _,
                    actions,
                    _,
                    test_recurrent_hidden_states,
                ) = self.actor_critic.act(
                    batch,
                    test_recurrent_hidden_states,
                    prev_actions,
                    not_done_masks,
                    deterministic=False,
                )

                prev_actions.copy_(actions)

            outputs = self.envs.step([a[0].item() for a in actions])

            observations, rewards, dones, infos = [
                list(x) for x in zip(*outputs)
            ]
            batch = batch_obs(observations, device=self.device)

            if self._static_encoder:
                batch["prev_visual_features"] = step_batch["visual_features"]
                batch["visual_features"] = self._encoder(batch)

            not_done_masks = torch.tensor(
                [[0.0] if done else [1.0] for done in dones],
                dtype=torch.float,
                device=self.device,
            )

            rewards = torch.tensor(rewards,
                                   dtype=torch.float,
                                   device=self.device).unsqueeze(1)
            current_episode_reward += rewards
            next_episodes = self.envs.current_episodes()
            envs_to_pause = []
            n_envs = self.envs.num_envs
            for i in range(n_envs):
                if (
                        next_episodes[i].scene_id,
                        next_episodes[i].episode_id,
                ) in stats_episodes:
                    envs_to_pause.append(i)

                # episode ended
                if not_done_masks[i].item() == 0:
                    pbar.update()
                    episode_stats = dict()
                    episode_stats["reward"] = current_episode_reward[i].item()
                    episode_stats.update(
                        self._extract_scalars_from_info(infos[i]))
                    current_episode_reward[i] = 0
                    # use scene_id + episode_id as unique id for storing stats
                    stats_episodes[(
                        current_episodes[i].scene_id,
                        current_episodes[i].episode_id,
                    )] = episode_stats

                    if len(self.config.VIDEO_OPTION) > 0:
                        generate_video(
                            video_option=self.config.VIDEO_OPTION,
                            video_dir=self.config.VIDEO_DIR,
                            images=rgb_frames[i],
                            episode_id=current_episodes[i].episode_id,
                            checkpoint_idx=checkpoint_index,
                            metrics=self._extract_scalars_from_info(infos[i]),
                            tb_writer=writer,
                        )

                        rgb_frames[i] = []

                # episode continues
                elif len(self.config.VIDEO_OPTION) > 0:
                    frame = observations_to_image(observations[i], infos[i])
                    rgb_frames[i].append(frame)

            (
                self.envs,
                test_recurrent_hidden_states,
                not_done_masks,
                current_episode_reward,
                prev_actions,
                batch,
                rgb_frames,
            ) = self._pause_envs(
                envs_to_pause,
                self.envs,
                test_recurrent_hidden_states,
                not_done_masks,
                current_episode_reward,
                prev_actions,
                batch,
                rgb_frames,
            )

        num_episodes = len(stats_episodes)
        aggregated_stats = dict()
        for stat_key in next(iter(stats_episodes.values())).keys():
            aggregated_stats[stat_key] = (
                sum([v[stat_key]
                     for v in stats_episodes.values()]) / num_episodes)

        for k, v in aggregated_stats.items():
            logger.info(f"Average episode {k}: {v:.4f}")

        step_id = checkpoint_index
        if "extra_state" in ckpt_dict and "step" in ckpt_dict["extra_state"]:
            step_id = ckpt_dict["extra_state"]["step"]

        writer.add_scalars(
            "eval_reward",
            {"average reward": aggregated_stats["reward"]},
            step_id,
        )

        metrics = {k: v for k, v in aggregated_stats.items() if k != "reward"}
        if len(metrics) > 0:
            writer.add_scalars("eval_metrics", metrics, step_id)

        self.envs.close()
コード例 #2
0
class PPOTrainer(BaseRLTrainer):
    r"""Trainer class for PPO algorithm
    Paper: https://arxiv.org/abs/1707.06347.
    """
    supported_tasks = ["Nav-v0"]

    def __init__(self, config=None):
        super().__init__(config)
        self.actor_critic = None
        self.agent = None
        self.envs = None
        if config is not None:
            logger.info(f"config: {config}")

        self._static_encoder = False
        self._encoder = None

    def _setup_actor_critic_agent(self, ppo_cfg: Config) -> None:
        r"""Sets up actor critic and agent for PPO.

        Args:
            ppo_cfg: config node with relevant params

        Returns:
            None
        """
        logger.add_filehandler(self.config.LOG_FILE)

        self.actor_critic = PointNavBaselinePolicy(
            observation_space=self.envs.observation_spaces[0],
            action_space=self.envs.action_spaces[0],
            hidden_size=ppo_cfg.hidden_size,
            goal_sensor_uuid=self.config.TASK_CONFIG.TASK.GOAL_SENSOR_UUID,
        )
        self.actor_critic.to(self.device)

        self.agent = PPO(
            actor_critic=self.actor_critic,
            clip_param=ppo_cfg.clip_param,
            ppo_epoch=ppo_cfg.ppo_epoch,
            num_mini_batch=ppo_cfg.num_mini_batch,
            value_loss_coef=ppo_cfg.value_loss_coef,
            entropy_coef=ppo_cfg.entropy_coef,
            lr=ppo_cfg.lr,
            eps=ppo_cfg.eps,
            max_grad_norm=ppo_cfg.max_grad_norm,
            use_normalized_advantage=ppo_cfg.use_normalized_advantage,
        )

    def save_checkpoint(self,
                        file_name: str,
                        extra_state: Optional[Dict] = None) -> None:
        r"""Save checkpoint with specified name.

        Args:
            file_name: file name for checkpoint

        Returns:
            None
        """
        checkpoint = {
            "state_dict": self.agent.state_dict(),
            "config": self.config,
        }
        if extra_state is not None:
            checkpoint["extra_state"] = extra_state

        torch.save(checkpoint,
                   os.path.join(self.config.CHECKPOINT_FOLDER, file_name))

    def load_checkpoint(self, checkpoint_path: str, *args, **kwargs) -> Dict:
        r"""Load checkpoint of specified path as a dict.

        Args:
            checkpoint_path: path of target checkpoint
            *args: additional positional args
            **kwargs: additional keyword args

        Returns:
            dict containing checkpoint info
        """
        return torch.load(checkpoint_path, *args, **kwargs)

    def _collect_rollout_step(self, rollouts, current_episode_reward,
                              episode_rewards, episode_counts):
        pth_time = 0.0
        env_time = 0.0

        t_sample_action = time.time()
        # sample actions
        with torch.no_grad():
            step_observation = {
                k: v[rollouts.step]
                for k, v in rollouts.observations.items()
            }

            (
                values,
                actions,
                actions_log_probs,
                recurrent_hidden_states,
            ) = self.actor_critic.act(
                step_observation,
                rollouts.recurrent_hidden_states[rollouts.step],
                rollouts.prev_actions[rollouts.step],
                rollouts.masks[rollouts.step],
            )

        pth_time += time.time() - t_sample_action

        t_step_env = time.time()

        outputs = self.envs.step([a[0].item() for a in actions])
        observations, rewards, dones, infos = [list(x) for x in zip(*outputs)]

        env_time += time.time() - t_step_env

        t_update_stats = time.time()
        batch = batch_obs(observations)
        rewards = torch.tensor(rewards,
                               dtype=torch.float,
                               device=episode_rewards.device)
        rewards = rewards.unsqueeze(1)

        masks = torch.tensor(
            [[0.0] if done else [1.0] for done in dones],
            dtype=torch.float,
            device=episode_rewards.device,
        )

        current_episode_reward += rewards
        episode_rewards += (1 - masks) * current_episode_reward
        episode_counts += 1 - masks
        current_episode_reward *= masks

        if self._static_encoder:
            with torch.no_grad():
                batch["visual_features"] = self._encoder(batch)

        rollouts.insert(
            batch,
            recurrent_hidden_states,
            actions,
            actions_log_probs,
            values,
            rewards,
            masks,
        )

        pth_time += time.time() - t_update_stats

        return pth_time, env_time, self.envs.num_envs

    def _update_agent(self, ppo_cfg, rollouts):
        t_update_model = time.time()
        with torch.no_grad():
            last_observation = {
                k: v[rollouts.step]
                for k, v in rollouts.observations.items()
            }
            next_value = self.actor_critic.get_value(
                last_observation,
                rollouts.recurrent_hidden_states[rollouts.step],
                rollouts.prev_actions[rollouts.step],
                rollouts.masks[rollouts.step],
            ).detach()

        rollouts.compute_returns(next_value, ppo_cfg.use_gae, ppo_cfg.gamma,
                                 ppo_cfg.tau)

        value_loss, action_loss, dist_entropy = self.agent.update(rollouts)

        rollouts.after_update()

        return (
            time.time() - t_update_model,
            value_loss,
            action_loss,
            dist_entropy,
        )

    def train(self) -> None:
        r"""Main method for training PPO.

        Returns:
            None
        """

        self.envs = construct_envs(self.config,
                                   get_env_class(self.config.ENV_NAME))

        ppo_cfg = self.config.RL.PPO
        self.device = (torch.device("cuda", self.config.TORCH_GPU_ID)
                       if torch.cuda.is_available() else torch.device("cpu"))
        if not os.path.isdir(self.config.CHECKPOINT_FOLDER):
            os.makedirs(self.config.CHECKPOINT_FOLDER)
        self._setup_actor_critic_agent(ppo_cfg)
        logger.info("agent number of parameters: {}".format(
            sum(param.numel() for param in self.agent.parameters())))

        rollouts = RolloutStorage(
            ppo_cfg.num_steps,
            self.envs.num_envs,
            self.envs.observation_spaces[0],
            self.envs.action_spaces[0],
            ppo_cfg.hidden_size,
        )
        rollouts.to(self.device)

        observations = self.envs.reset()
        batch = batch_obs(observations)

        for sensor in rollouts.observations:
            rollouts.observations[sensor][0].copy_(batch[sensor])

        # batch and observations may contain shared PyTorch CUDA
        # tensors.  We must explicitly clear them here otherwise
        # they will be kept in memory for the entire duration of training!
        batch = None
        observations = None

        episode_rewards = torch.zeros(self.envs.num_envs, 1)
        episode_counts = torch.zeros(self.envs.num_envs, 1)
        current_episode_reward = torch.zeros(self.envs.num_envs, 1)
        window_episode_reward = deque(maxlen=ppo_cfg.reward_window_size)
        window_episode_counts = deque(maxlen=ppo_cfg.reward_window_size)

        t_start = time.time()
        env_time = 0
        pth_time = 0
        count_steps = 0
        count_checkpoints = 0

        lr_scheduler = LambdaLR(
            optimizer=self.agent.optimizer,
            lr_lambda=lambda x: linear_decay(x, self.config.NUM_UPDATES),
        )

        with TensorboardWriter(self.config.TENSORBOARD_DIR,
                               flush_secs=self.flush_secs) as writer:
            for update in range(self.config.NUM_UPDATES):
                if ppo_cfg.use_linear_lr_decay:
                    lr_scheduler.step()

                if ppo_cfg.use_linear_clip_decay:
                    self.agent.clip_param = ppo_cfg.clip_param * linear_decay(
                        update, self.config.NUM_UPDATES)

                for step in range(ppo_cfg.num_steps):
                    (
                        delta_pth_time,
                        delta_env_time,
                        delta_steps,
                    ) = self._collect_rollout_step(
                        rollouts,
                        current_episode_reward,
                        episode_rewards,
                        episode_counts,
                    )
                    pth_time += delta_pth_time
                    env_time += delta_env_time
                    count_steps += delta_steps

                (
                    delta_pth_time,
                    value_loss,
                    action_loss,
                    dist_entropy,
                ) = self._update_agent(ppo_cfg, rollouts)
                pth_time += delta_pth_time

                window_episode_reward.append(episode_rewards.clone())
                window_episode_counts.append(episode_counts.clone())

                losses = [value_loss, action_loss]
                stats = zip(
                    ["count", "reward"],
                    [window_episode_counts, window_episode_reward],
                )
                deltas = {
                    k:
                    ((v[-1] -
                      v[0]).sum().item() if len(v) > 1 else v[0].sum().item())
                    for k, v in stats
                }
                deltas["count"] = max(deltas["count"], 1.0)

                writer.add_scalar("reward", deltas["reward"] / deltas["count"],
                                  count_steps)

                writer.add_scalars(
                    "losses",
                    {k: l
                     for l, k in zip(losses, ["value", "policy"])},
                    count_steps,
                )

                # log stats
                if update > 0 and update % self.config.LOG_INTERVAL == 0:
                    logger.info("update: {}\tfps: {:.3f}\t".format(
                        update, count_steps / (time.time() - t_start)))

                    logger.info(
                        "update: {}\tenv-time: {:.3f}s\tpth-time: {:.3f}s\t"
                        "frames: {}".format(update, env_time, pth_time,
                                            count_steps))

                    window_rewards = (window_episode_reward[-1] -
                                      window_episode_reward[0]).sum()
                    window_counts = (window_episode_counts[-1] -
                                     window_episode_counts[0]).sum()

                    if window_counts > 0:
                        logger.info(
                            "Average window size {} reward: {:3f}".format(
                                len(window_episode_reward),
                                (window_rewards / window_counts).item(),
                            ))
                    else:
                        logger.info("No episodes finish in current window")

                # checkpoint model
                if update % self.config.CHECKPOINT_INTERVAL == 0:
                    self.save_checkpoint(f"ckpt.{count_checkpoints}.pth",
                                         dict(step=count_steps))
                    count_checkpoints += 1

            self.envs.close()

    def _eval_checkpoint(
        self,
        checkpoint_path: str,
        writer: TensorboardWriter,
        checkpoint_index: int = 0,
    ) -> None:
        r"""Evaluates a single checkpoint.

        Args:
            checkpoint_path: path of checkpoint
            writer: tensorboard writer object for logging to tensorboard
            checkpoint_index: index of cur checkpoint for logging

        Returns:
            None
        """
        # Map location CPU is almost always better than mapping to a CUDA device.
        ckpt_dict = self.load_checkpoint(checkpoint_path, map_location="cpu")

        if self.config.EVAL.USE_CKPT_CONFIG:
            config = self._setup_eval_config(ckpt_dict["config"])
        else:
            config = self.config.clone()

        ppo_cfg = config.RL.PPO

        config.defrost()
        config.TASK_CONFIG.DATASET.SPLIT = config.EVAL.SPLIT
        config.freeze()

        if len(self.config.VIDEO_OPTION) > 0:
            config.defrost()
            config.TASK_CONFIG.TASK.MEASUREMENTS.append("TOP_DOWN_MAP")
            config.TASK_CONFIG.TASK.MEASUREMENTS.append("COLLISIONS")
            config.freeze()

        logger.info(f"env config: {config}")
        self.envs = construct_envs(config, get_env_class(config.ENV_NAME))
        self._setup_actor_critic_agent(ppo_cfg)

        self.agent.load_state_dict(ckpt_dict["state_dict"])
        self.actor_critic = self.agent.actor_critic

        # get name of performance metric, e.g. "spl"
        metric_name = self.config.TASK_CONFIG.TASK.MEASUREMENTS[0]
        metric_cfg = getattr(self.config.TASK_CONFIG.TASK, metric_name)
        measure_type = baseline_registry.get_measure(metric_cfg.TYPE)
        assert measure_type is not None, "invalid measurement type {}".format(
            metric_cfg.TYPE)
        self.metric_uuid = measure_type(sim=None, task=None,
                                        config=None)._get_uuid()

        observations = self.envs.reset()
        batch = batch_obs(observations, self.device)

        current_episode_reward = torch.zeros(self.envs.num_envs,
                                             1,
                                             device=self.device)

        test_recurrent_hidden_states = torch.zeros(
            self.actor_critic.net.num_recurrent_layers,
            self.config.NUM_PROCESSES,
            ppo_cfg.hidden_size,
            device=self.device,
        )
        prev_actions = torch.zeros(self.config.NUM_PROCESSES,
                                   1,
                                   device=self.device,
                                   dtype=torch.long)
        not_done_masks = torch.zeros(self.config.NUM_PROCESSES,
                                     1,
                                     device=self.device)
        stats_episodes = dict()  # dict of dicts that stores stats per episode

        rgb_frames = [[] for _ in range(self.config.NUM_PROCESSES)
                      ]  # type: List[List[np.ndarray]]
        if len(self.config.VIDEO_OPTION) > 0:
            os.makedirs(self.config.VIDEO_DIR, exist_ok=True)

        pbar = tqdm.tqdm(total=self.config.TEST_EPISODE_COUNT)
        self.actor_critic.eval()
        while (len(stats_episodes) < self.config.TEST_EPISODE_COUNT
               and self.envs.num_envs > 0):
            current_episodes = self.envs.current_episodes()

            with torch.no_grad():
                (
                    _,
                    actions,
                    _,
                    test_recurrent_hidden_states,
                ) = self.actor_critic.act(
                    batch,
                    test_recurrent_hidden_states,
                    prev_actions,
                    not_done_masks,
                    deterministic=False,
                )

                prev_actions.copy_(actions)

            outputs = self.envs.step([a[0].item() for a in actions])

            observations, rewards, dones, infos = [
                list(x) for x in zip(*outputs)
            ]
            batch = batch_obs(observations, self.device)

            not_done_masks = torch.tensor(
                [[0.0] if done else [1.0] for done in dones],
                dtype=torch.float,
                device=self.device,
            )

            rewards = torch.tensor(rewards,
                                   dtype=torch.float,
                                   device=self.device).unsqueeze(1)
            current_episode_reward += rewards
            next_episodes = self.envs.current_episodes()
            envs_to_pause = []
            n_envs = self.envs.num_envs
            for i in range(n_envs):
                if (
                        next_episodes[i].scene_id,
                        next_episodes[i].episode_id,
                ) in stats_episodes:
                    envs_to_pause.append(i)

                # episode ended
                if not_done_masks[i].item() == 0:
                    pbar.update()
                    episode_stats = dict()
                    episode_stats[self.metric_uuid] = infos[i][
                        self.metric_uuid]
                    episode_stats["success"] = int(
                        infos[i][self.metric_uuid] > 0)
                    episode_stats["reward"] = current_episode_reward[i].item()
                    current_episode_reward[i] = 0
                    # use scene_id + episode_id as unique id for storing stats
                    stats_episodes[(
                        current_episodes[i].scene_id,
                        current_episodes[i].episode_id,
                    )] = episode_stats

                    if len(self.config.VIDEO_OPTION) > 0:
                        generate_video(
                            video_option=self.config.VIDEO_OPTION,
                            video_dir=self.config.VIDEO_DIR,
                            images=rgb_frames[i],
                            episode_id=current_episodes[i].episode_id,
                            checkpoint_idx=checkpoint_index,
                            metric_name=self.metric_uuid,
                            metric_value=infos[i][self.metric_uuid],
                            tb_writer=writer,
                        )

                        rgb_frames[i] = []

                # episode continues
                elif len(self.config.VIDEO_OPTION) > 0:
                    frame = observations_to_image(observations[i], infos[i])
                    rgb_frames[i].append(frame)

            (
                self.envs,
                test_recurrent_hidden_states,
                not_done_masks,
                current_episode_reward,
                prev_actions,
                batch,
                rgb_frames,
            ) = self._pause_envs(
                envs_to_pause,
                self.envs,
                test_recurrent_hidden_states,
                not_done_masks,
                current_episode_reward,
                prev_actions,
                batch,
                rgb_frames,
            )

        aggregated_stats = dict()
        for stat_key in next(iter(stats_episodes.values())).keys():
            aggregated_stats[stat_key] = sum(
                [v[stat_key] for v in stats_episodes.values()])
        num_episodes = len(stats_episodes)

        episode_reward_mean = aggregated_stats["reward"] / num_episodes
        episode_metric_mean = aggregated_stats[self.metric_uuid] / num_episodes
        episode_success_mean = aggregated_stats["success"] / num_episodes

        logger.info(f"Average episode reward: {episode_reward_mean:.6f}")
        logger.info(f"Average episode success: {episode_success_mean:.6f}")
        logger.info(
            f"Average episode {self.metric_uuid}: {episode_metric_mean:.6f}")

        step_id = checkpoint_index
        if "extra_state" in ckpt_dict and "step" in ckpt_dict["extra_state"]:
            step_id = ckpt_dict["extra_state"]["step"]

        writer.add_scalars("eval_reward",
                           {"average reward": episode_reward_mean}, step_id)
        writer.add_scalars(
            f"eval_{self.metric_uuid}",
            {f"average {self.metric_uuid}": episode_metric_mean},
            step_id,
        )
        writer.add_scalars("eval_success",
                           {"average success": episode_success_mean}, step_id)

        self.envs.close()