def get_predict_config(attention_mask_type, use_relative_attention,
                       bos_special_attention):
  """Constructs a config for prediction."""
  base_config = base_models.TransformerConfig(
      vocab_size=io_vocab_size,
      output_vocab_size=program_vocab_size,
      shift=True,
      emb_dim=embedding_dim,
      num_heads=num_heads,
      num_layers=num_layers,
      qkv_dim=embedding_dim,
      mlp_dim=hidden_dim,
      max_len=max(max_characters, max_program_length),
      use_relative_attention=use_relative_attention,
      deterministic=not use_dropout,
      decode=False,
      bos_token=bos_token)
  predict_config = models.DecomposeAttentionTransformerConfig(
      base_config=base_config.replace(
          shift=False,
          deterministic=not use_dropout,
          decode=not slow_decode),
      attention_mask_type=attention_mask_type,
      bos_special_attention=bos_special_attention)
  return predict_config
예제 #2
0
def main(_):
    tf.enable_v2_behavior()

    tf.random.set_seed(FLAGS.seed)
    np.random.seed(FLAGS.seed)
    random.seed(FLAGS.seed)

    # BOS special attention only makes sense if we are using relative attention
    # and it's not the baseline.
    if FLAGS.bos_special_attention and (not FLAGS.use_relative_attention
                                        or FLAGS.attention_mask_type
                                        == 'baseline'):
        raise ValueError(
            "bos_special_attention doesn't work when use_relative_attention={} and "
            'attention_mask_type={}'.format(FLAGS.use_relative_attention,
                                            FLAGS.attention_mask_type))

    if not gfile.isdir(FLAGS.save_dir):
        gfile.makedirs(FLAGS.save_dir)

    hparam_str_dict = json.loads(FLAGS.xm_parameters)
    hparam_str = ','.join([
        '%s=%s' % (shorten(k), str(hparam_str_dict[k]))
        for k in hparam_str_dict.keys()
    ])

    # Number of local devices for this host.
    n_devices = jax.local_device_count()

    if jax.host_id() == 0:
        summary_writer = tensorboard.SummaryWriter(
            os.path.join(FLAGS.save_dir, 'tb', hparam_str))

    batch_size = FLAGS.per_device_batch_size * n_devices
    io_shape = (FLAGS.per_device_batch_size, FLAGS.num_strings_per_task,
                FLAGS.max_characters)
    predict_io_shape = (FLAGS.per_device_batch_size,
                        FLAGS.num_strings_per_task,
                        FLAGS.predict_max_characters)
    program_shape = (FLAGS.per_device_batch_size, FLAGS.max_program_length)

    # Setup DSL
    # ---------------------------------------------------------------------------

    # Build token tables.
    id_char_table = {i + 1: char for (i, char) in enumerate(dsl.CHARACTER)}
    char_id_table = {char: id for id, char in id_char_table.items()}
    id_token_table, token_id_table = dsl_tokens.build_token_tables()
    io_vocab_size = len(char_id_table) + 1  # For padding.
    program_vocab_size = len(token_id_table) + 1

    bos_token = token_id_table[dsl.BOS]
    eos_token = token_id_table[dsl.EOS]

    # Parse io and program token sequences (for eval).
    def decode_io(inputs, outputs):
        """Decode io examples tokens."""
        def decode_str(s):
            """Decode string tokens."""
            return ''.join([id_char_table[c_id] for c_id in s if c_id > 0])

        inps, outs = [], []
        for inp, out in zip(inputs, outputs):
            inps.append(decode_str(inp))
            outs.append(decode_str(out))
        return inps, outs

    def decode_program(program):
        """Decode program tokens."""
        program = program[:np.argmax(program == eos_token) + 1].astype(
            np.int32)
        program = program[program != bos_token]

        try:
            return dsl.decode_program(program.tolist(), id_token_table)
        except:  # pylint: disable=bare-except
            return None  # Program does not compile.

    # Load Dataset
    # ---------------------------------------------------------------------------
    logging.info('Initializing dataset.')
    if not FLAGS.dataset_filepattern:
        raise ValueError('Must specify filepattern to dataset.')

    # Training dataset.
    logging.info('Loading dataset from %s', FLAGS.dataset_filepattern)
    padded_shapes = (io_shape[1:], io_shape[1:], program_shape[1:])
    logging.info('padded_shapes: %s', padded_shapes)
    dataset = input_pipeline.create_dataset_from_tf_record(
        FLAGS.dataset_filepattern, token_id_table, char_id_table)
    dataset = dataset.padded_batch(batch_size,
                                   padded_shapes=padded_shapes,
                                   drop_remainder=True)
    # Split evaluation and training.
    eval_ds = dataset.take(FLAGS.num_eval_steps)
    # Decrease batch of predict dataset to handle beam search.
    predict_padded_shapes = (predict_io_shape[1:], predict_io_shape[1:],
                             program_shape[1:])
    logging.info('predict_padded_shapes: %s', predict_padded_shapes)
    predict_ds = eval_ds.unbatch().padded_batch(
        int(np.ceil(batch_size / 10)), padded_shapes=predict_padded_shapes)
    train_ds = dataset.skip(FLAGS.num_eval_steps)
    if FLAGS.train_set_batches > 0:
        train_ds = train_ds.take(FLAGS.train_set_batches)
    train_ds = train_ds.repeat()

    test_dataset = input_pipeline.create_dataset_from_tf_record(
        FLAGS.test_dataset_filepattern, token_id_table, char_id_table)
    test_dataset = test_dataset.padded_batch(
        batch_size, padded_shapes=predict_padded_shapes, drop_remainder=False)
    quick_test_dataset = (test_dataset.take(
        FLAGS.num_quick_test_steps).unbatch().padded_batch(
            int(np.ceil(batch_size / 10)),
            padded_shapes=predict_padded_shapes))
    final_test_dataset = (test_dataset.take(
        FLAGS.num_final_test_steps).unbatch().padded_batch(
            int(np.ceil(batch_size / 10)),
            padded_shapes=predict_padded_shapes))

    # Build Model and Optimizer
    # ---------------------------------------------------------------------------
    default_config = base_models.TransformerConfig(
        vocab_size=io_vocab_size, output_vocab_size=program_vocab_size)
    base_config = base_models.TransformerConfig(
        vocab_size=io_vocab_size,
        output_vocab_size=program_vocab_size,
        shift=True,
        emb_dim=FLAGS.embedding_dim,
        num_heads=FLAGS.num_heads,
        num_layers=FLAGS.num_layers,
        qkv_dim=FLAGS.embedding_dim,
        mlp_dim=FLAGS.hidden_dim,
        max_len=max(FLAGS.max_characters, FLAGS.max_program_length),
        dropout_rate=FLAGS.dropout_rate,
        attention_dropout_rate=FLAGS.attention_dropout_rate,
        use_relative_attention=FLAGS.use_relative_attention,
        deterministic=False,
        decode=False,
        bos_token=bos_token,
        num_input_relative_position_buckets=FLAGS.num_position_buckets,
        max_input_distance=min(FLAGS.max_distance,
                               default_config.max_input_distance),
        num_output_relative_position_buckets=FLAGS.num_position_buckets,
        max_output_distance=min(FLAGS.max_distance,
                                default_config.max_output_distance),
        num_input_cross_output_relative_position_buckets=(
            FLAGS.num_position_buckets),
        max_input_cross_output_distance=min(
            FLAGS.max_distance,
            default_config.max_input_cross_output_distance),
        num_program_relative_position_buckets=FLAGS.num_position_buckets,
        max_program_distance=min(FLAGS.max_distance,
                                 default_config.max_program_distance),
        num_program_cross_embed_relative_position_buckets=(
            FLAGS.num_position_buckets),
        max_program_cross_embed_distance=min(
            FLAGS.max_distance,
            default_config.max_program_cross_embed_distance),
        bidirectional_program_attention=FLAGS.bidirectional_program_attention)
    train_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config,
        attention_mask_type=FLAGS.attention_mask_type,
        bos_special_attention=FLAGS.bos_special_attention)
    eval_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config.replace(deterministic=True),
        attention_mask_type=FLAGS.attention_mask_type,
        bos_special_attention=FLAGS.bos_special_attention)
    predict_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config.replace(
            shift=False,
            deterministic=True,
            decode=not FLAGS.slow_decode,
            max_len=max(FLAGS.max_characters, FLAGS.max_program_length,
                        FLAGS.predict_max_characters)),
        attention_mask_type=FLAGS.attention_mask_type,
        bos_special_attention=FLAGS.bos_special_attention)

    rng = jax.random.PRNGKey(FLAGS.seed)
    rng = jax.random.fold_in(rng, jax.host_id())
    rng, init_rng = jax.random.split(rng)

    dropout_rng = jax.random.split(rng, jax.local_device_count())
    del rng

    m = models.DecomposeAttentionTransformer(eval_config)
    initial_variables = jax.jit(m.init)(init_rng,
                                        jnp.ones(io_shape, jnp.float32),
                                        jnp.ones(io_shape, jnp.float32),
                                        jnp.ones(program_shape, jnp.float32))

    optimizer_def = optim.Adam(FLAGS.lr,
                               beta1=0.9,
                               beta2=0.98,
                               eps=1e-9,
                               weight_decay=FLAGS.weight_decay)
    optimizer = optimizer_def.create(initial_variables['params'])

    del initial_variables  # Don't keep a copy of the initial model.

    start_step = 0
    if FLAGS.restore_checkpoints:
        # Restore unreplicated optimizer + model state from last checkpoint.
        optimizer = checkpoints.restore_checkpoint(
            os.path.join(FLAGS.save_dir, 'checkpoints', hparam_str), optimizer)
        # Grab last step.
        start_step = int(optimizer.state.step)
        logging.info('Found model checkpointed at step %d.', start_step)
        if FLAGS.finetune_start_step > 0:
            logging.info(
                'Checking that start_step (%s) == finetune_start_step (%s)',
                start_step, FLAGS.finetune_start_step)
            assert start_step >= FLAGS.finetune_start_step
            steps_to_skip = start_step - FLAGS.finetune_start_step
        else:
            steps_to_skip = start_step

        # TODO(kshi): It is likely that this code can lead to the job stalling for
        # 10+ hours when restarting from a checkpoint that had been trained a long
        # time, possibly because dataset skipping is slow.
        logging.info('Skipping %s steps...', steps_to_skip)
        train_ds = train_ds.skip(steps_to_skip)
        dummy_p_train_step = jax.pmap(
            lambda dropout_rng: jax.random.split(dropout_rng)[1])
        for _ in range(steps_to_skip):
            dropout_rng = dummy_p_train_step(dropout_rng)
        logging.info('Finished skipping steps')
        logging.info('Host %s has dropout_rng = %s', jax.host_id(),
                     dropout_rng)

    # Replicate optimizer.
    optimizer = jax_utils.replicate(optimizer)

    # TODO(jxihong): Implement fast decoding.
    assert FLAGS.slow_decode, 'Fast decoding is not implemented yet.'

    if FLAGS.finetune_start_step <= 0:
        learning_rate_fn = create_learning_rate_scheduler(
            base_learning_rate=FLAGS.lr)
    else:
        # Constant LR for finetuning.
        learning_rate_fn = create_learning_rate_scheduler(
            base_learning_rate=FLAGS.lr, factors='constant')
    p_train_step = jax.pmap(functools.partial(
        train_step, learning_rate_fn=learning_rate_fn, config=train_config),
                            axis_name='batch')
    p_eval_step = jax.pmap(functools.partial(eval_step,
                                             eos_token=eos_token,
                                             config=eval_config),
                           axis_name='batch')
    p_init_cache = jax.pmap(functools.partial(
        initialize_cache,
        max_decode_len=FLAGS.max_program_length,
        config=predict_config),
                            axis_name='batch')
    p_pred_step = jax.pmap(functools.partial(
        predict_step,
        eos_token=eos_token,
        max_decode_len=FLAGS.max_program_length,
        config=predict_config,
        slow_decode=FLAGS.slow_decode),
                           axis_name='batch',
                           static_broadcasted_argnums=(4, ))

    # Main Train Loop
    # ---------------------------------------------------------------------------

    logging.info('Starting training!')
    metrics_all = []
    tick = time.time()
    train_iter = train_ds.as_numpy_iterator()
    for step in range(start_step, FLAGS.num_train_steps):
        inputs, outputs, programs = common_utils.shard(next(train_iter))

        optimizer, metrics, dropout_rng = p_train_step(optimizer,
                                                       inputs,
                                                       outputs,
                                                       programs,
                                                       dropout_rng=dropout_rng)
        metrics_all.append(metrics)
        is_last_step = step == FLAGS.num_train_steps - 1

        # Save a Checkpoint
        if (step % FLAGS.checkpoint_freq == 0 and step > 0) or is_last_step:
            if jax.host_id() == 0:
                # Save unreplicated optimizer + model state.
                checkpoints.save_checkpoint(
                    os.path.join(FLAGS.save_dir, 'checkpoints', hparam_str),
                    jax_utils.unreplicate(optimizer), step)

        # Periodic metric handling.

        # Training Metrics
        if (step and step % FLAGS.log_freq == 0) or is_last_step:
            logging.info('Gathering training metrics.')
            metrics_all = common_utils.get_metrics(metrics_all)
            lr = metrics_all.pop('learning_rate').mean()
            metrics_sums = jax.tree_map(jnp.sum, metrics_all)
            denominator = metrics_sums.pop('denominator')
            summary = jax.tree_map(
                lambda x: x / denominator,  # pylint: disable=cell-var-from-loop
                metrics_sums)
            summary['learning_rate'] = lr
            # Calculate (clipped) perplexity after averaging log-perplexities:
            summary['perplexity'] = jnp.clip(jnp.exp(summary['loss']),
                                             a_max=1.0e4)

            if jax.host_id() == 0:
                logging.info('Train in step: %d, loss: %.4f', step,
                             summary['loss'])
                tock = time.time()
                steps_per_sec = FLAGS.log_freq / (tock - tick)
                tick = tock
                summary_writer.scalar('train/steps per second', steps_per_sec,
                                      step)
                for key, val in summary.items():
                    summary_writer.scalar('train/' + key, val, step)
                summary_writer.flush()
            # Reset metric accumulation for next evaluation cycle.
            metrics_all = []

        # Evaluation Metrics
        if (step and step % FLAGS.eval_freq == 0) or is_last_step:
            logging.info('Gathering evaluation metrics.')
            t_evaluation_start = time.time()
            eval_metrics = []
            for batches in eval_ds.as_numpy_iterator():
                inputs, outputs, programs = common_utils.shard(batches)

                metrics = p_eval_step(optimizer.target, inputs, outputs,
                                      programs)
                eval_metrics.append(metrics)

            eval_metrics = common_utils.get_metrics(eval_metrics)
            eval_metrics_sums = jax.tree_map(jnp.sum, eval_metrics)
            eval_denominator = eval_metrics_sums.pop('denominator')
            eval_summary = jax.tree_map(
                lambda x: x / eval_denominator,  # pylint: disable=cell-var-from-loop
                eval_metrics_sums)

            if jax.host_id() == 0:
                logging.info('Evaluation time: %.4f s step %d, loss: %.4f.',
                             time.time() - t_evaluation_start, step,
                             eval_summary['loss'])
                for key, val in eval_summary.items():
                    summary_writer.scalar('eval/' + key, val, step)
                summary_writer.flush()

        # Beam search metrics.
        if (step and step % FLAGS.predict_freq == 0) or is_last_step:
            logging.info('Gathering beam search metrics.')
            test_ds = final_test_dataset if is_last_step else quick_test_dataset

            for dataset, predict_or_test in [(predict_ds, 'predict'),
                                             (test_ds, 'test')]:

                for beam_size in [1, 10]:
                    t_inference_start = time.time()
                    total_successes = 0
                    total_denominator = 0
                    pred_successes = collections.defaultdict(int)
                    pred_denominators = collections.defaultdict(int)

                    ios, targets, predictions, top_of_beams = [], [], [], []
                    for batches in dataset.as_numpy_iterator():
                        pred_batch = batches
                        # Handle final odd-sized batch by padding instead of dropping it.
                        cur_pred_batch_size = pred_batch[0].shape[0]
                        if cur_pred_batch_size % n_devices:
                            padded_size = int(
                                np.ceil(cur_pred_batch_size / n_devices) *
                                n_devices)
                            # pylint: disable=cell-var-from-loop
                            pred_batch = jax.tree_map(
                                lambda x: pad_examples(x, padded_size),
                                pred_batch)
                        inputs, outputs, programs = common_utils.shard(
                            pred_batch)

                        cache = (p_init_cache(inputs, outputs, programs)
                                 if not FLAGS.slow_decode else None)
                        predicted = p_pred_step(optimizer.target, inputs,
                                                outputs, cache, beam_size)
                        predicted = tohost(predicted)
                        inputs, outputs, programs = map(
                            tohost, (inputs, outputs, programs))

                        for i, beams in enumerate(predicted):
                            inps, outs = decode_io(inputs[i], outputs[i])
                            p, p_score = eval_predicted(
                                beams,
                                inps,
                                outs,
                                parse_beam_fn=decode_program)

                            # Split by length of program.
                            program = programs[i]
                            num_expressions = len(
                                decode_program(program).expressions)
                            pred_denominators[num_expressions] += 1
                            total_denominator += 1
                            if p_score >= len(inps):
                                pred_successes[num_expressions] += 1
                                total_successes += 1

                            ios.append(' ; '.join(map(str, zip(inps, outs))))
                            targets.append(
                                decode_program(programs[i]).to_string())
                            try:
                                predictions.append(p.to_string())
                            except:  # pylint: disable=bare-except
                                predictions.append('Did not compile')
                            logging.info('ios: %s', ios[-1])
                            logging.info('target: %s', targets[-1])
                            beams_log = []
                            for beam in beams:
                                try:
                                    beams_log.append(
                                        decode_program(beam).to_string())
                                except:  # pylint: disable=bare-except
                                    beams_log.append('Did not compile')
                            logging.info('predicted beam: %s',
                                         '\n'.join(beams_log))

                            top_of_beam = []
                            for index, beam in enumerate(beams[:-5:-1]):
                                try:
                                    decoded_program = decode_program(
                                        beam).to_string()
                                except:  # pylint: disable=bare-except
                                    decoded_program = 'Did not compile'
                                top_of_beam.append(
                                    'index: {}, decoded: {}, tokens: {}'.
                                    format(index, decoded_program, beam))
                            top_of_beams.append('\n\n'.join(top_of_beam))

                    all_total_successes, all_total_denominator = per_host_sum_pmap(
                        jax.tree_map(np.array,
                                     (total_successes, total_denominator)))
                    all_pred_successes, all_pred_denominators = per_host_sum_pmap(
                        jax.tree_map(np.array,
                                     (pred_successes, pred_denominators)))

                    # Record beam search results as text summaries.
                    message = []
                    for n in np.random.choice(np.arange(len(predictions)), 8):
                        text = (f'ios: {ios[n]}\n\ntarget: {targets[n]}\n\n'
                                f'predicted: {predictions[n]}\n\n'
                                f'top of beam:\n\n{top_of_beams[n]}\n\n')
                        message.append(text)

                    # Write to tensorboard.
                    if jax.host_id() == 0:
                        accuracy = 100 * all_total_successes / all_total_denominator
                        logging.info(
                            '%s results, step %d, beam size %d: %s / %s = %.2f%% (%.2f s)',
                            predict_or_test, step, beam_size,
                            all_total_successes, all_total_denominator,
                            accuracy,
                            time.time() - t_inference_start)
                        summary_writer.scalar(
                            '{}/beam-size-{}'.format(predict_or_test,
                                                     beam_size), accuracy,
                            step)

                        for length in sorted(all_pred_successes.keys()):
                            this_length_accuracy = (
                                100 * all_pred_successes[length] /
                                all_pred_denominators[length])
                            logging.info(
                                '  accuracy for length %s: %s / %s = %.2f%%',
                                length, all_pred_successes[length],
                                all_pred_denominators[length],
                                this_length_accuracy)
                            summary_writer.scalar(
                                '{}-by-length/beam-size-{}-length-{}'.format(
                                    predict_or_test, beam_size, length),
                                this_length_accuracy, step)

                        summary_writer.text(
                            '{}-samples-beam-{}'.format(
                                predict_or_test, beam_size),
                            '\n------\n'.join(message), step)
                        summary_writer.flush()
예제 #3
0
def main(_):
    tf.enable_v2_behavior()

    tf.random.set_seed(FLAGS.seed)
    np.random.seed(FLAGS.seed)
    random.seed(FLAGS.seed)

    if not gfile.isdir(FLAGS.save_dir):
        gfile.mkdir(FLAGS.save_dir)

    hparam_str_dict = dict(seed=FLAGS.seed, lr=FLAGS.lr)
    # Get hyperparmaters
    if FLAGS.xm_parameters:
        for key, value in json.loads(FLAGS.xm_parameters).items():
            if key not in hparam_str_dict:
                hparam_str_dict[key] = value

    hparam_str = ','.join([
        '%s=%s' % (shorten(k), str(hparam_str_dict[k]))
        for k in sorted(hparam_str_dict.keys())
    ])

    # Number of local devices for this host.
    n_devices = jax.local_device_count()

    if jax.host_id() == 0:
        summary_writer = tensorboard.SummaryWriter(
            os.path.join(FLAGS.save_dir, 'tb', hparam_str))

    batch_size = FLAGS.per_device_batch_size * n_devices
    io_shape = (FLAGS.per_device_batch_size, FLAGS.num_strings_per_task,
                FLAGS.max_characters)
    program_shape = (FLAGS.per_device_batch_size, FLAGS.max_program_length)

    # Setup DSL
    # ---------------------------------------------------------------------------

    # Build token tables.
    id_char_table = {i + 1: char for (i, char) in enumerate(dsl.CHARACTER)}
    char_id_table = {char: id for id, char in id_char_table.items()}
    id_token_table, token_id_table = dsl_tokens.build_token_tables()
    io_vocab_size = len(char_id_table) + 1  # For padding.
    program_vocab_size = len(token_id_table) + 1

    bos_token = token_id_table[dsl.BOS]
    eos_token = token_id_table[dsl.EOS]

    # Parse io and program token sequences (for eval).
    def decode_io(inputs, outputs):
        """Decode io examples tokens."""
        def decode_str(s):
            """Decode string tokens."""
            return ''.join([id_char_table[c_id] for c_id in s if c_id > 0])

        inps, outs = [], []
        for inp, out in zip(inputs, outputs):
            inps.append(decode_str(inp))
            outs.append(decode_str(out))
        return inps, outs

    def decode_program(program):
        """Decode program tokens."""
        program = program[:np.argmax(program == eos_token) + 1].astype(
            np.int32)
        program = program[program != bos_token]

        try:
            return dsl.decode_program(program, id_token_table)
        except:  # pylint: disable=bare-except
            return None  # Program does not compile.

    # Load Dataset
    # ---------------------------------------------------------------------------
    logging.info('Initializing dataset.')
    if not FLAGS.dataset_filepattern:
        raise ValueError('Must specify filepattern to dataset.')

    # Training dataset.
    dataset = input_pipeline.create_dataset_from_tf_record(
        FLAGS.dataset_filepattern, token_id_table, char_id_table)
    dataset = dataset.padded_batch(batch_size,
                                   padded_shapes=(io_shape[1:], io_shape[1:],
                                                  program_shape[1:]),
                                   drop_remainder=True)
    # Split evaluation and training.
    eval_ds = dataset.take(FLAGS.num_eval_steps)
    # Decrease batch of predict dataset to handle beam search.
    predict_ds = eval_ds.unbatch().padded_batch(
        int(np.ceil(batch_size / 10)),
        padded_shapes=(io_shape[1:], io_shape[1:], program_shape[1:]))
    train_ds = dataset.skip(FLAGS.num_eval_steps).repeat()
    train_iter = train_ds.as_numpy_iterator()

    # Build Model and Optimizer
    # ---------------------------------------------------------------------------
    base_config = base_models.TransformerConfig(
        vocab_size=io_vocab_size,
        output_vocab_size=program_vocab_size,
        shift=True,
        emb_dim=FLAGS.embedding_dim,
        num_heads=FLAGS.num_heads,
        num_layers=FLAGS.num_layers,
        qkv_dim=FLAGS.embedding_dim,
        mlp_dim=FLAGS.hidden_dim,
        max_len=max(FLAGS.max_characters, FLAGS.max_program_length),
        use_relative_attention=FLAGS.use_relative_attention,
        num_relative_position_buckets=FLAGS.num_relative_position_buckets,
        deterministic=False,
        decode=False,
        bos_token=bos_token)
    train_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config, attention_mask_type=FLAGS.attention_mask_type)
    eval_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config.replace(deterministic=True),
        attention_mask_type=FLAGS.attention_mask_type)
    predict_config = models.DecomposeAttentionTransformerConfig(
        base_config=base_config.replace(shift=False,
                                        deterministic=True,
                                        decode=not FLAGS.slow_decode),
        attention_mask_type=FLAGS.attention_mask_type)

    rng = jax.random.PRNGKey(FLAGS.seed)
    rng = jax.random.fold_in(rng, jax.host_id())
    rng, init_rng = jax.random.split(rng)

    m = models.DecomposeAttentionTransformer(eval_config)
    initial_variables = jax.jit(m.init)(init_rng,
                                        jnp.ones(io_shape, jnp.float32),
                                        jnp.ones(io_shape, jnp.float32),
                                        jnp.ones(program_shape, jnp.float32))

    optimizer_def = optim.Adam(FLAGS.lr,
                               beta1=0.9,
                               beta2=0.98,
                               eps=1e-9,
                               weight_decay=FLAGS.weight_decay)
    optimizer = optimizer_def.create(initial_variables['params'])

    del initial_variables  # Don't keep a copy of the initial model.

    start_step = 0
    if FLAGS.restore_checkpoints:
        # Restore unreplicated optimizer + model state from last checkpoint.
        optimizer = checkpoints.restore_checkpoint(
            os.path.join(FLAGS.save_dir, 'checkpoints', hparam_str), optimizer)
        # Grab last step.
        start_step = int(optimizer.state.step)
        logging.info('Found model checkpointed at step %d.', start_step)

    # Replicate optimizer.
    optimizer = jax_utils.replicate(optimizer)

    # TODO(jxihong): Implement fast decoding.
    assert FLAGS.slow_decode, 'Fast decoding is not implemented yet.'

    learning_rate_fn = create_learning_rate_scheduler(
        base_learning_rate=FLAGS.lr)
    p_train_step = jax.pmap(functools.partial(
        train_step, learning_rate_fn=learning_rate_fn, config=train_config),
                            axis_name='batch')
    p_eval_step = jax.pmap(functools.partial(eval_step,
                                             eos_token=eos_token,
                                             config=eval_config),
                           axis_name='batch')
    p_init_cache = jax.pmap(functools.partial(
        initialize_cache,
        max_decode_len=FLAGS.max_program_length,
        config=predict_config),
                            axis_name='batch')
    p_pred_step = jax.pmap(functools.partial(
        predict_step,
        eos_token=eos_token,
        max_decode_len=FLAGS.max_program_length,
        config=predict_config,
        slow_decode=FLAGS.slow_decode),
                           axis_name='batch',
                           static_broadcasted_argnums=(4, ))

    # Main Train Loop
    # ---------------------------------------------------------------------------
    train_rngs = jax.random.split(rng, jax.local_device_count())
    del rng

    metrics_all = []
    tick = time.time()
    for step in range(start_step, FLAGS.num_train_steps):
        inputs, outputs, programs = common_utils.shard(next(train_iter))

        optimizer, metrics, train_rngs = p_train_step(optimizer,
                                                      inputs,
                                                      outputs,
                                                      programs,
                                                      train_rng=train_rngs)
        metrics_all.append(metrics)
        is_last_step = step == FLAGS.num_train_steps - 1

        # Save a Checkpoint
        if (step % FLAGS.checkpoint_freq == 0 and step > 0) or is_last_step:
            if jax.host_id() == 0:
                # Save unreplicated optimizer + model state.
                checkpoints.save_checkpoint(
                    os.path.join(FLAGS.save_dir, 'checkpoints', hparam_str),
                    jax_utils.unreplicate(optimizer), step)

        # Periodic metric handling.
        if not step or (step % FLAGS.log_freq != 0 and not is_last_step):
            continue

        logging.info('Gathering training metrics.')
        # Training Metrics
        metrics_all = common_utils.get_metrics(metrics_all)
        lr = metrics_all.pop('learning_rate').mean()
        metrics_sums = jax.tree_map(jnp.sum, metrics_all)
        denominator = metrics_sums.pop('denominator')
        summary = jax.tree_map(
            lambda x: x / denominator,  # pylint: disable=cell-var-from-loop
            metrics_sums)
        summary['learning_rate'] = lr
        # Calculate (clipped) perplexity after averaging log-perplexities:
        summary['perplexity'] = jnp.clip(jnp.exp(summary['loss']), a_max=1.0e4)

        if jax.host_id() == 0:
            logging.info('Train in step: %d, loss: %.4f', step,
                         summary['loss'])
            tock = time.time()
            steps_per_sec = FLAGS.log_freq / (tock - tick)
            tick = tock
            summary_writer.scalar('train/steps per second', steps_per_sec,
                                  step)
            for key, val in summary.items():
                summary_writer.scalar('train/' + key, val, step)
            summary_writer.flush()
        # Reset metric accumulation for next evaluation cycle.
        metrics_all = []

        # Evaluation Metrics
        logging.info('Gathering evaluation metrics.')
        t_evaluation_start = time.time()
        eval_metrics = []
        for batches in eval_ds.as_numpy_iterator():
            inputs, outputs, programs = common_utils.shard(batches)

            metrics = p_eval_step(optimizer.target, inputs, outputs, programs)
            eval_metrics.append(metrics)

        eval_metrics = common_utils.get_metrics(eval_metrics)
        eval_metrics_sums = jax.tree_map(jnp.sum, eval_metrics)
        eval_denominator = eval_metrics_sums.pop('denominator')
        eval_summary = jax.tree_map(
            lambda x: x / eval_denominator,  # pylint: disable=cell-var-from-loop
            eval_metrics_sums)

        if jax.host_id() == 0:
            logging.info('Evaluation time: %.4f s step %d, loss: %.4f.',
                         time.time() - t_evaluation_start, step,
                         eval_summary['loss'])
            for key, val in eval_summary.items():
                summary_writer.scalar('eval/' + key, val, step)
            summary_writer.flush()

        # Beam search metrics.
        logging.info('Gathering beam search metrics.')
        for beam_size in [1, 10, 12, 24, 48, 96]:
            t_inference_start = time.time()
            pred_acc = 0
            pred_denominator = 0

            ios, targets, predictions = [], [], []
            for batches in predict_ds.as_numpy_iterator():
                pred_batch = batches
                # Handle final odd-sized batch by padding instead of dropping it.
                cur_pred_batch_size = pred_batch[0].shape[0]
                if cur_pred_batch_size % n_devices:
                    padded_size = int(
                        np.ceil(cur_pred_batch_size / n_devices) * n_devices)
                    # pylint: disable=cell-var-from-loop
                    pred_batch = jax.tree_map(
                        lambda x: pad_examples(x, padded_size), pred_batch)
                inputs, outputs, programs = common_utils.shard(pred_batch)

                cache = (p_init_cache(inputs, outputs, programs)
                         if not FLAGS.slow_decode else None)
                predicted = p_pred_step(optimizer.target, inputs, outputs,
                                        cache, beam_size)
                predicted = tohost(predicted)
                inputs, outputs, programs = map(tohost,
                                                (inputs, outputs, programs))

                pred_denominator += programs.shape[0]
                for i, beams in enumerate(predicted):
                    inps, outs = decode_io(inputs[i], outputs[i])
                    p, p_score = eval_predicted(beams,
                                                inps,
                                                outs,
                                                parse_beam_fn=decode_program)
                    if p_score >= len(inps):
                        pred_acc += 1
                    ios.append(' ; '.join(map(str, zip(inps, outs))))
                    targets.append(decode_program(programs[i]).to_string())
                    try:
                        predictions.append(p.to_string())
                    except:  # pylint: disable=bare-except
                        predictions.append('')
                    logging.info('ios: %s', ios[-1])
                    logging.info('target: %s', targets[-1])
                    beams_log = []
                    for beam in beams:
                        try:
                            beams_log.append(decode_program(beam).to_string())
                        except:  # pylint: disable=bare-except
                            beams_log.append('None')
                    logging.info('predicted beam: %s', '\n'.join(beams_log))

            all_pred_acc, all_pred_denominator = per_host_sum_pmap(
                jax.tree_map(np.array, (pred_acc, pred_denominator)))

            # Record beam search results as text summaries.
            message = []
            for n in np.random.choice(np.arange(len(predictions)), 8):
                text = (f'ios: {ios[n]}\n\ntarget: {targets[n]}\n\n'
                        f'predicted: {predictions[n]}\n\n')
                message.append(text)

            # Write to tensorboard.
            if jax.host_id() == 0:
                slow_or_fast = 'slow' if FLAGS.slow_decode else 'fast'
                logging.info(
                    'Prediction time, %s (beam %d): %.4f s, step %d, score %.4f',
                    slow_or_fast, beam_size,
                    time.time() - t_inference_start, step,
                    all_pred_acc / all_pred_denominator)
                summary_writer.scalar(
                    'predict-{}/score-{}'.format(slow_or_fast, beam_size),
                    all_pred_acc / all_pred_denominator, step)
                summary_writer.text('samples-{}'.format(beam_size),
                                    '\n------\n'.join(message), step)
                summary_writer.flush()