def train()

in src/algos/curiosity.py [0:0]


def train(flags): 
    if flags.xpid is None:
        flags.xpid = 'curiosity-%s' % time.strftime('%Y%m%d-%H%M%S')
    plogger = file_writer.FileWriter(
        xpid=flags.xpid,
        xp_args=flags.__dict__,
        rootdir=flags.savedir,
    )

    checkpointpath = os.path.expandvars(os.path.expanduser(
            '%s/%s/%s' % (flags.savedir, flags.xpid,'model.tar')))

    T = flags.unroll_length
    B = flags.batch_size

    flags.device = None
    if not flags.disable_cuda and torch.cuda.is_available():
        log.info('Using CUDA.')
        flags.device = torch.device('cuda')
    else:
        log.info('Not using CUDA.')
        flags.device = torch.device('cpu')

    env = create_env(flags)
    if flags.num_input_frames > 1:
        env = FrameStack(env, flags.num_input_frames)  

    if 'MiniGrid' in flags.env:
        if flags.use_fullobs_policy:
            model = FullObsMinigridPolicyNet(env.observation_space.shape, env.action_space.n)                        
        else:
            model = MinigridPolicyNet(env.observation_space.shape, env.action_space.n)                        
        if flags.use_fullobs_intrinsic:
            state_embedding_model = FullObsMinigridStateEmbeddingNet(env.observation_space.shape)\
                .to(device=flags.device) 
        else:
            state_embedding_model = MinigridStateEmbeddingNet(env.observation_space.shape)\
                .to(device=flags.device) 
        forward_dynamics_model = MinigridForwardDynamicsNet(env.action_space.n)\
            .to(device=flags.device) 
        inverse_dynamics_model = MinigridInverseDynamicsNet(env.action_space.n)\
            .to(device=flags.device) 
    else:
        model = MarioDoomPolicyNet(env.observation_space.shape, env.action_space.n)
        state_embedding_model = MarioDoomStateEmbeddingNet(env.observation_space.shape)\
            .to(device=flags.device) 
        forward_dynamics_model = MarioDoomForwardDynamicsNet(env.action_space.n)\
            .to(device=flags.device) 
        inverse_dynamics_model = MarioDoomInverseDynamicsNet(env.action_space.n)\
            .to(device=flags.device) 

    buffers = create_buffers(env.observation_space.shape, model.num_actions, flags)
    model.share_memory()
    
    initial_agent_state_buffers = []
    for _ in range(flags.num_buffers):
        state = model.initial_state(batch_size=1)
        for t in state:
            t.share_memory_()
        initial_agent_state_buffers.append(state)

    actor_processes = []
    ctx = mp.get_context('fork')
    free_queue = ctx.SimpleQueue()
    full_queue = ctx.SimpleQueue()
    
    episode_state_count_dict = dict()
    train_state_count_dict = dict()
    for i in range(flags.num_actors):
        actor = ctx.Process(
            target=act,
            args=(i, free_queue, full_queue, model, buffers, 
                episode_state_count_dict, train_state_count_dict, 
                initial_agent_state_buffers, flags))
        actor.start()
        actor_processes.append(actor)
  
    if 'MiniGrid' in flags.env: 
        if flags.use_fullobs_policy:
            learner_model = FullObsMinigridPolicyNet(env.observation_space.shape, env.action_space.n)\
                .to(device=flags.device)
        else:
            learner_model = MinigridPolicyNet(env.observation_space.shape, env.action_space.n)\
                .to(device=flags.device)
    else:
        learner_model = MarioDoomPolicyNet(env.observation_space.shape, env.action_space.n)\
            .to(device=flags.device)

    optimizer = torch.optim.RMSprop(
        learner_model.parameters(),
        lr=flags.learning_rate,
        momentum=flags.momentum,
        eps=flags.epsilon,
        alpha=flags.alpha)
    
    state_embedding_optimizer = torch.optim.RMSprop(
        state_embedding_model.parameters(),
        lr=flags.learning_rate,
        momentum=flags.momentum,
        eps=flags.epsilon,
        alpha=flags.alpha)
    
    inverse_dynamics_optimizer = torch.optim.RMSprop(
        inverse_dynamics_model.parameters(),
        lr=flags.learning_rate,
        momentum=flags.momentum,
        eps=flags.epsilon,
        alpha=flags.alpha)
    
    forward_dynamics_optimizer = torch.optim.RMSprop(
        forward_dynamics_model.parameters(),
        lr=flags.learning_rate,
        momentum=flags.momentum,
        eps=flags.epsilon,
        alpha=flags.alpha)
    
    
    def lr_lambda(epoch):
        return 1 - min(epoch * T * B, flags.total_frames) / flags.total_frames

    scheduler = torch.optim.lr_scheduler.LambdaLR(optimizer, lr_lambda)

    logger = logging.getLogger('logfile')
    stat_keys = [
        'total_loss',
        'mean_episode_return',
        'pg_loss',
        'baseline_loss',
        'entropy_loss',
        'forward_dynamics_loss',
        'inverse_dynamics_loss',
        'mean_rewards',
        'mean_intrinsic_rewards',
        'mean_total_rewards',
    ]

    logger.info('# Step\t%s', '\t'.join(stat_keys))

    frames, stats = 0, {}


    def batch_and_learn(i, lock=threading.Lock()):
        """Thread target for the learning process."""
        nonlocal frames, stats
        timings = prof.Timings()
        while frames < flags.total_frames:
            timings.reset()
            batch, agent_state = get_batch(free_queue, full_queue, buffers, 
                initial_agent_state_buffers, flags, timings)
            stats = learn(model, learner_model, state_embedding_model, forward_dynamics_model, 
                          inverse_dynamics_model, batch, agent_state, optimizer, 
                          state_embedding_optimizer, forward_dynamics_optimizer, 
                          inverse_dynamics_optimizer, scheduler, flags, frames=frames)
            timings.time('learn')
            with lock:
                to_log = dict(frames=frames)
                to_log.update({k: stats[k] for k in stat_keys})
                plogger.log(to_log)
                frames += T * B

        if i == 0:
            log.info('Batch and learn: %s', timings.summary())

    for m in range(flags.num_buffers):
        free_queue.put(m)

    threads = []    
    for i in range(flags.num_threads):
        thread = threading.Thread(
            target=batch_and_learn, name='batch-and-learn-%d' % i, args=(i,))
        thread.start()
        threads.append(thread)


    def checkpoint(frames):
        if flags.disable_checkpoint:
            return
        checkpointpath = os.path.expandvars(
            os.path.expanduser('%s/%s/%s' % (flags.savedir, flags.xpid,
            'model.tar')))
        log.info('Saving checkpoint to %s', checkpointpath)
        torch.save({
            'model_state_dict': model.state_dict(),
            'state_embedding_model_state_dict': state_embedding_model.state_dict(),
            'forward_dynamics_model_state_dict': forward_dynamics_model.state_dict(),
            'inverse_dynamics_model_state_dict': inverse_dynamics_model.state_dict(),
            'optimizer_state_dict': optimizer.state_dict(),
            'state_embedding_optimizer_state_dict': state_embedding_optimizer.state_dict(),
            'forward_dynamics_optimizer_state_dict': forward_dynamics_optimizer.state_dict(),
            'inverse_dynamics_optimizer_state_dict': inverse_dynamics_optimizer.state_dict(),
            'scheduler_state_dict': scheduler.state_dict(),
            'flags': vars(flags),
        }, checkpointpath)

    timer = timeit.default_timer
    try:
        last_checkpoint_time = timer()
        while frames < flags.total_frames:
            start_frames = frames
            start_time = timer()
            time.sleep(5)

            if timer() - last_checkpoint_time > flags.save_interval * 60: 
                checkpoint(frames)
                last_checkpoint_time = timer()

            fps = (frames - start_frames) / (timer() - start_time)
            
            if stats.get('episode_returns', None):
                mean_return = 'Return per episode: %.1f. ' % stats[
                    'mean_episode_return']
            else:
                mean_return = ''

            total_loss = stats.get('total_loss', float('inf'))
            if stats:
                log.info('After %i frames: loss %f @ %.1f fps. Mean Return %.1f. \n Stats \n %s', \
                        frames, total_loss, fps, stats['mean_episode_return'], pprint.pformat(stats))

    except KeyboardInterrupt:
        return 
    else:
        for thread in threads:
            thread.join()
        log.info('Learning finished after %d frames.', frames)
    finally:
        for _ in range(flags.num_actors):
            free_queue.put(None)
        for actor in actor_processes:
            actor.join(timeout=1)

    checkpoint(frames)
    plogger.close()