<reponame>mickelliu/ray<gh_stars>1-10
"""
Distributed Prioritized Experience Replay (Ape-X)
=================================================

This file defines a DQN trainer using the Ape-X architecture.

Ape-X uses a single GPU learner and many CPU workers for experience collection.
Experience collection can scale to hundreds of CPU workers due to the
distributed prioritization of experience prior to storage in replay buffers.

Detailed documentation:
https://docs.ray.io/en/master/rllib-algorithms.html#distributed-prioritized-experience-replay-ape-x
"""  # noqa: E501

import collections
import copy
import platform
from typing import Tuple

import ray
from ray.actor import ActorHandle
from ray.rllib.agents.dqn.dqn import calculate_rr_weights, \
    DEFAULT_CONFIG as DQN_DEFAULT_CONFIG, DQNTrainer
from ray.rllib.agents.dqn.learner_thread import LearnerThread
from ray.rllib.evaluation.worker_set import WorkerSet
from ray.rllib.execution.common import (STEPS_TRAINED_COUNTER,
                                        STEPS_TRAINED_THIS_ITER_COUNTER,
                                        _get_global_vars, _get_shared_metrics)
from ray.rllib.execution.concurrency_ops import Concurrently, Dequeue, Enqueue
from ray.rllib.execution.metric_ops import StandardMetricsReporting
from ray.rllib.execution.buffers.multi_agent_replay_buffer import ReplayActor
from ray.rllib.execution.replay_ops import Replay, StoreToReplayBuffer
from ray.rllib.execution.rollout_ops import ParallelRollouts
from ray.rllib.execution.train_ops import UpdateTargetNetwork
from ray.rllib.utils import merge_dicts
from ray.rllib.utils.actors import create_colocated_actors
from ray.rllib.utils.annotations import override
from ray.rllib.utils.metrics.learner_info import LEARNER_INFO
from ray.rllib.utils.typing import SampleBatchType, TrainerConfigDict
from ray.tune.trainable import Trainable
from ray.tune.utils.placement_groups import PlacementGroupFactory
from ray.util.iter import LocalIterator

# yapf: disable
# __sphinx_doc_begin__
APEX_DEFAULT_CONFIG = merge_dicts(
    # See also the options in dqn.py, which are also supported.
    DQN_DEFAULT_CONFIG,
    {
        "optimizer": merge_dicts(
            DQN_DEFAULT_CONFIG["optimizer"], {
                "max_weight_sync_delay": 400,
                "num_replay_buffer_shards": 4,
                "debug": False
            }),
        "n_step": 3,
        "num_gpus": 1,
        "num_workers": 32,

        "buffer_size": 2000000,
        # TODO(jungong) : add proper replay_buffer_config after
        #     DistributedReplayBuffer type is supported.
        "replay_buffer_config": None,
        # Whether all shards of the replay buffer must be co-located
        # with the learner process (running the execution plan).
        # This is preferred b/c the learner process should have quick
        # access to the data from the buffer shards, avoiding network
        # traffic each time samples from the buffer(s) are drawn.
        # Set this to False for relaxing this constraint and allowing
        # replay shards to be created on node(s) other than the one
        # on which the learner is located.
        "replay_buffer_shards_colocated_with_driver": True,

        "learning_starts": 50000,
        "train_batch_size": 512,
        "rollout_fragment_length": 50,
        "target_network_update_freq": 500000,
        "timesteps_per_iteration": 25000,
        "exploration_config": {"type": "PerWorkerEpsilonGreedy"},
        "worker_side_prioritization": True,
        "min_iter_time_s": 30,
        # If set, this will fix the ratio of replayed from a buffer and learned
        # on timesteps to sampled from an environment and stored in the replay
        # buffer timesteps. Otherwise, replay will proceed as fast as possible.
        "training_intensity": None,
    },
)
# __sphinx_doc_end__
# yapf: enable


# Update worker weights as they finish generating experiences.
class UpdateWorkerWeights:
    def __init__(self, learner_thread: LearnerThread, workers: WorkerSet,
                 max_weight_sync_delay: int):
        self.learner_thread = learner_thread
        self.workers = workers
        self.steps_since_update = collections.defaultdict(int)
        self.max_weight_sync_delay = max_weight_sync_delay
        self.weights = None

    def __call__(self, item: Tuple[ActorHandle, SampleBatchType]):
        actor, batch = item
        self.steps_since_update[actor] += batch.count
        if self.steps_since_update[actor] >= self.max_weight_sync_delay:
            # Note that it's important to pull new weights once
            # updated to avoid excessive correlation between actors.
            if self.weights is None or self.learner_thread.weights_updated:
                self.learner_thread.weights_updated = False
                self.weights = ray.put(
                    self.workers.local_worker().get_weights())
            actor.set_weights.remote(self.weights, _get_global_vars())
            # Also update global vars of the local worker.
            self.workers.local_worker().set_global_vars(_get_global_vars())
            self.steps_since_update[actor] = 0
            # Update metrics.
            metrics = _get_shared_metrics()
            metrics.counters["num_weight_syncs"] += 1


class ApexTrainer(DQNTrainer):
    @classmethod
    @override(DQNTrainer)
    def get_default_config(cls) -> TrainerConfigDict:
        return APEX_DEFAULT_CONFIG

    @override(DQNTrainer)
    def validate_config(self, config):
        if config["num_gpus"] > 1:
            raise ValueError("`num_gpus` > 1 not yet supported for APEX-DQN!")
        # Call DQN's validation method.
        super().validate_config(config)

    @staticmethod
    @override(DQNTrainer)
    def execution_plan(workers: WorkerSet, config: dict,
                       **kwargs) -> LocalIterator[dict]:
        assert len(kwargs) == 0, (
            "Apex execution_plan does NOT take any additional parameters")

        # Create a number of replay buffer actors.
        num_replay_buffer_shards = config["optimizer"][
            "num_replay_buffer_shards"]

        replay_actor_args = [
            num_replay_buffer_shards,
            config["learning_starts"],
            config["buffer_size"],
            config["train_batch_size"],
            config["prioritized_replay_alpha"],
            config["prioritized_replay_beta"],
            config["prioritized_replay_eps"],
            config["multiagent"]["replay_mode"],
            config.get("replay_sequence_length", 1),
        ]
        # Place all replay buffer shards on the same node as the learner
        # (driver process that runs this execution plan).
        if config["replay_buffer_shards_colocated_with_driver"]:
            replay_actors = create_colocated_actors(
                actor_specs=[
                    # (class, args, kwargs={}, count)
                    (ReplayActor, replay_actor_args, {},
                     num_replay_buffer_shards)
                ],
                node=platform.node(),  # localhost
            )[0]  # [0]=only one item in `actor_specs`.
        # Place replay buffer shards on any node(s).
        else:
            replay_actors = [
                ReplayActor(*replay_actor_args)
                for _ in range(num_replay_buffer_shards)
            ]

        # Start the learner thread.
        learner_thread = LearnerThread(workers.local_worker())
        learner_thread.start()

        # Update experience priorities post learning.
        def update_prio_and_stats(item: Tuple[ActorHandle, dict, int]) -> None:
            actor, prio_dict, count = item
            if config.get("prioritized_replay"):
                actor.update_priorities.remote(prio_dict)
            metrics = _get_shared_metrics()
            # Manually update the steps trained counter since the learner
            # thread is executing outside the pipeline.
            metrics.counters[STEPS_TRAINED_THIS_ITER_COUNTER] = count
            metrics.counters[STEPS_TRAINED_COUNTER] += count
            metrics.timers["learner_dequeue"] = learner_thread.queue_timer
            metrics.timers["learner_grad"] = learner_thread.grad_timer
            metrics.timers["learner_overall"] = learner_thread.overall_timer

        # We execute the following steps concurrently:
        # (1) Generate rollouts and store them in one of our replay buffer
        # actors. Update the weights of the worker that generated the batch.
        rollouts = ParallelRollouts(workers, mode="async", num_async=2)
        store_op = rollouts \
            .for_each(StoreToReplayBuffer(actors=replay_actors))
        # Only need to update workers if there are remote workers.
        if workers.remote_workers():
            store_op = store_op.zip_with_source_actor() \
                .for_each(UpdateWorkerWeights(
                    learner_thread, workers,
                    max_weight_sync_delay=(
                        config["optimizer"]["max_weight_sync_delay"])))

        # (2) Read experiences from one of the replay buffer actors and send
        # to the learner thread via its in-queue.
        post_fn = config.get("before_learn_on_batch") or (lambda b, *a: b)
        replay_op = Replay(actors=replay_actors, num_async=4) \
            .for_each(lambda x: post_fn(x, workers, config)) \
            .zip_with_source_actor() \
            .for_each(Enqueue(learner_thread.inqueue))

        # (3) Get priorities back from learner thread and apply them to the
        # replay buffer actors.
        update_op = Dequeue(
            learner_thread.outqueue, check=learner_thread.is_alive) \
            .for_each(update_prio_and_stats) \
            .for_each(UpdateTargetNetwork(
                workers, config["target_network_update_freq"],
                by_steps_trained=True))

        if config["training_intensity"]:
            # Execute (1), (2) with a fixed intensity ratio.
            rr_weights = calculate_rr_weights(config) + ["*"]
            merged_op = Concurrently(
                [store_op, replay_op, update_op],
                mode="round_robin",
                output_indexes=[2],
                round_robin_weights=rr_weights)
        else:
            # Execute (1), (2), (3) asynchronously as fast as possible. Only
            # output items from (3) since metrics aren't available before
            # then.
            merged_op = Concurrently(
                [store_op, replay_op, update_op],
                mode="async",
                output_indexes=[2])

        # Add in extra replay and learner metrics to the training result.
        def add_apex_metrics(result: dict) -> dict:
            replay_stats = ray.get(replay_actors[0].stats.remote(
                config["optimizer"].get("debug")))
            exploration_infos = workers.foreach_trainable_policy(
                lambda p, _: p.get_exploration_state())
            result["info"].update({
                "exploration_infos": exploration_infos,
                "learner_queue": learner_thread.learner_queue_size.stats(),
                LEARNER_INFO: copy.deepcopy(learner_thread.learner_info),
                "replay_shard_0": replay_stats,
            })
            return result

        # Only report metrics from the workers with the lowest 1/3 of
        # epsilons.
        selected_workers = workers.remote_workers()[
            -len(workers.remote_workers()) // 3:]

        return StandardMetricsReporting(
            merged_op, workers, config,
            selected_workers=selected_workers).for_each(add_apex_metrics)

    @classmethod
    @override(Trainable)
    def default_resource_request(cls, config):
        cf = dict(cls.get_default_config(), **config)

        eval_config = cf["evaluation_config"]

        # Return PlacementGroupFactory containing all needed resources
        # (already properly defined as device bundles).
        return PlacementGroupFactory(
            bundles=[{
                # Local worker + replay buffer actors.
                # Force replay buffers to be on same node to maximize
                # data bandwidth between buffers and the learner (driver).
                # Replay buffer actors each contain one shard of the total
                # replay buffer and use 1 CPU each.
                "CPU": cf["num_cpus_for_driver"] +
                cf["optimizer"]["num_replay_buffer_shards"],
                "GPU": 0 if cf["_fake_gpus"] else cf["num_gpus"],
            }] + [
                {
                    # RolloutWorkers.
                    "CPU": cf["num_cpus_per_worker"],
                    "GPU": cf["num_gpus_per_worker"],
                } for _ in range(cf["num_workers"])
            ] + ([
                {
                    # Evaluation workers.
                    # Note: The local eval worker is located on the driver
                    # CPU.
                    "CPU": eval_config.get("num_cpus_per_worker",
                                           cf["num_cpus_per_worker"]),
                    "GPU": eval_config.get("num_gpus_per_worker",
                                           cf["num_gpus_per_worker"]),
                } for _ in range(cf["evaluation_num_workers"])
            ] if cf["evaluation_interval"] else []),
            strategy=config.get("placement_strategy", "PACK"))
