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ray-project--ray/rllib/examples/envs/async_gym_env_vectorization.py
2026-07-13 13:17:40 +08:00

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Python

"""Example demo'ing async gym vector envs, in which sub-envs have their own process.
Setting up env vectorization works through setting the `config.num_envs_per_env_runner`
value to > 1. However, by default the n sub-environments are stepped through
sequentially, rather than in parallel.
This script shows the effect of setting the `config.gym_env_vectorize_mode` from its
default value of "sync" (all sub envs are located in the same EnvRunner process)
to "async" (all sub envs in each EnvRunner get their own process).
This example:
- shows, which config settings to change in order to switch from sub-envs being
stepped in sequence to each sub-envs owning its own process (and compute resource)
and thus the vector being stepped in parallel.
- shows, how this setup can increase EnvRunner performance significantly, especially
for heavier, slower environments.
- uses an artificially slow CartPole-v1 environment for demonstration purposes.
How to run this script
----------------------
`python [script file name].py `
Use the `--vectorize-mode=both` option to run both modes (sync and async)
through Tune at the same time and get a better comparison of the throughputs
achieved.
For debugging, use the following additional command line options
`--no-tune --num-env-runners=0`
which should allow you to set breakpoints anywhere in the RLlib code and
have the execution stop there for inspection and debugging.
For logging to your WandB account, use:
`--wandb-key=[your WandB API key] --wandb-project=[some project name]
--wandb-run-name=[optional: WandB run name (within the defined project)]`
Results to expect
-----------------
You should see results similar to the following in your console output
when using the
+--------------------------+------------+------------------------+------+
| Trial name | status | gym_env_vectorize_mode | iter |
| | | | |
|--------------------------+------------+------------------------+------+
| PPO_slow-env_6ddf4_00000 | TERMINATED | sync | 4 |
| PPO_slow-env_6ddf4_00001 | TERMINATED | async | 4 |
+--------------------------+------------+------------------------+------+
+------------------+----------------------+------------------------+
| total time (s) | episode_return_mean | num_env_steps_sample |
| | | d_lifetime |
|------------------+----------------------+------------------------+
| 60.8794 | 73.53 | 16040 |
| 19.1203 | 73.86 | 16037 |
+------------------+----------------------+------------------------+
You can see that the async mode, given that the env is sufficiently slow,
achieves much better results when using vectorization.
You should see no difference, however, when only using
`--num-envs-per-env-runner=1`.
"""
import time
import gymnasium as gym
from ray import tune
from ray.rllib.algorithms.ppo import PPOConfig
from ray.rllib.examples.utils import (
add_rllib_example_script_args,
run_rllib_example_script_experiment,
)
parser = add_rllib_example_script_args(default_reward=60.0)
parser.set_defaults(
env="CartPole-v1",
num_envs_per_env_runner=6,
)
parser.add_argument(
"--vectorize-mode",
type=str,
default="async",
help="The value `gym.envs.registration.VectorizeMode` to use for env "
"vectorization. sync steps through all sub-envs in sequence. 'async' (default) "
"parallelizes sub-envs through multiprocessing and can speed up EnvRunners "
"significantly. Use the special value `both` to run both 'async' and 'sync' through a "
"Tune grid-search.",
)
class SlowEnv(gym.ObservationWrapper):
def observation(self, observation):
time.sleep(0.005)
return observation
if __name__ == "__main__":
args = parser.parse_args()
if args.no_tune and args.vectorize_mode == "both":
raise ValueError(
"Can't run this script with both --no-tune and --vectorize-mode=both!"
)
# Wrap the env with the slowness wrapper.
def _env_creator(cfg):
return SlowEnv(gym.make(args.env, **cfg))
tune.register_env("slow-env", _env_creator)
base_config = (
PPOConfig()
.environment("slow-env")
.env_runners(
gym_env_vectorize_mode=(
tune.grid_search(["sync", "async"])
if args.vectorize_mode == "both"
else args.vectorize_mode
),
)
)
results = run_rllib_example_script_experiment(base_config, args)
# Compare the throughputs and assert that ASYNC is much faster than SYNC.
if args.vectorize_mode == "both":
throughput_sync = (
results[0].metrics["num_env_steps_sampled_lifetime"]
/ results[0].metrics["time_total_s"]
)
throughput_async = (
results[1].metrics["num_env_steps_sampled_lifetime"]
/ results[1].metrics["time_total_s"]
)
assert throughput_async > throughput_sync