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"C++-based high-performance parallel environment execution engine (vectorized env) for general RL environments."

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EnvPool is a C++-based batched environment pool with pybind11 and thread pool. It has high performance (~1M raw FPS with Atari games, ~3M raw FPS with Mujoco simulator on DGX-A100) and compatible APIs (supports both gym and dm_env, both sync and async, both single and multi player environment). Currently it supports:

Here are EnvPool's several highlights:

Check out our arXiv paper for more details!



EnvPool is currently hosted on PyPI. It requires Python >= 3.7.

You can simply install EnvPool with the following command:

$ pip install envpool

After installation, open a Python console and type

import envpool

If no error occurs, you have successfully installed EnvPool.

From Source

Please refer to the guideline.


The tutorials and API documentation are hosted on

The example scripts are under examples/ folder; benchmark scripts are under benchmark/ folder.

Benchmark Results

We perform our benchmarks with ALE Atari environment PongNoFrameskip-v4 (with environment wrappers from OpenAI Baselines) and Mujoco environment Ant-v3 on different hardware setups, including a TPUv3-8 virtual machine (VM) of 96 CPU cores and 2 NUMA nodes, and an NVIDIA DGX-A100 of 256 CPU cores with 8 NUMA nodes. Baselines include 1) naive Python for-loop; 2) the most popular RL environment parallelization execution by Python subprocess, e.g., gym.vector_env; 3) to our knowledge, the fastest RL environment executor Sample Factory before EnvPool.

We report EnvPool performance with sync mode, async mode, and NUMA + async mode, compared with the baselines on different number of workers (i.e., number of CPU cores). As we can see from the results, EnvPool achieves significant improvements over the baselines on all settings. On the high-end setup, EnvPool achieves 1 Million frames per second with Atari and 3 Million frames per second with Mujoco on 256 CPU cores, which is 14.9x / 19.6x of the gym.vector_env baseline. On a typical PC setup with 12 CPU cores, EnvPool's throughput is 3.1x / 2.9x of gym.vector_env.

Atari Highest FPS Laptop (12) Workstation (32) TPU-VM (96) DGX-A100 (256)
For-loop 4,893 7,914 3,993 4,640
Subprocess 15,863 47,699 46,910 71,943
Sample-Factory 28,216 138,847 222,327 707,494
EnvPool (sync) 37,396 133,824 170,380 427,851
EnvPool (async) 49,439 200,428 359,559 891,286
EnvPool (numa+async) / / 373,169 1,069,922
Mujoco Highest FPS Laptop (12) Workstation (32) TPU-VM (96) DGX-A100 (256)
For-loop 12,861 20,298 10,474 11,569
Subprocess 36,586 105,432 87,403 163,656
Sample-Factory 62,510 309,264 461,515 1,573,262
EnvPool (sync) 66,622 380,950 296,681 949,787
EnvPool (async) 105,126 582,446 887,540 2,363,864
EnvPool (numa+async) / / 896,830 3,134,287

Please refer to the benchmark page for more details.

API Usage

The following content shows both synchronous and asynchronous API usage of EnvPool. You can also run the full script at examples/

Synchronous API

import envpool
import numpy as np

# make gym env
env = envpool.make("Pong-v5", env_type="gym", num_envs=100)
# or use envpool.make_gym(...)
obs = env.reset()  # should be (100, 4, 84, 84)
act = np.zeros(100, dtype=int)
obs, rew, term, trunc, info = env.step(act)

Under the synchronous mode, envpool closely resembles openai-gym/dm-env. It has the reset and step functions with the same meaning. However, there is one exception in envpool: batch interaction is the default. Therefore, during the creation of the envpool, there is a num_envs argument that denotes how many envs you like to run in parallel.

env = envpool.make("Pong-v5", env_type="gym", num_envs=100)

The first dimension of action passed to the step function should equal num_envs.

act = np.zeros(100, dtype=int)

You don't need to manually reset one environment when any of done is true; instead, all envs in envpool have enabled auto-reset by default.

Asynchronous API

import envpool
import numpy as np

# make asynchronous
num_envs = 64
batch_size = 16
env = envpool.make("Pong-v5", env_type="gym", num_envs=num_envs, batch_size=batch_size)
action_num = env.action_space.n
env.async_reset()  # send the initial reset signal to all envs
while True:
    obs, rew, term, trunc, info = env.recv()
    env_id = info["env_id"]
    action = np.random.randint(action_num, size=batch_size)
    env.send(action, env_id)

In the asynchronous mode, the step function is split into two parts: the send/recv functions. send takes two arguments, a batch of action, and the corresponding env_id that each action should be sent to. Unlike step, send does not wait for the envs to execute and return the next state, it returns immediately after the actions are fed to the envs. (The reason why it is called async mode).

env.send(action, env_id)

To get the "next states", we need to call the recv function. However, recv does not guarantee that you will get back the "next states" of the envs you just called send on. Instead, whatever envs finishes execution gets recved first.

state = env.recv()

Besides num_envs, there is one more argument batch_size. While num_envs defines how many envs in total are managed by the envpool, batch_size specifies the number of envs involved each time we interact with envpool. e.g. There are 64 envs executing in the envpool, send and recv each time interacts with a batch of 16 envs.

envpool.make("Pong-v5", env_type="gym", num_envs=64, batch_size=16)

There are other configurable arguments with envpool.make; please check out EnvPool Python interface introduction.


EnvPool is still under development. More environments will be added, and we always welcome contributions to help EnvPool better. If you would like to contribute, please check out our contribution guideline.


EnvPool is under Apache2 license.

Other third-party source-code and data are under their corresponding licenses.

We do not include their source code and data in this repo.

Citing EnvPool

If you find EnvPool useful, please cite it in your publications.

 author = {Weng, Jiayi and Lin, Min and Huang, Shengyi and Liu, Bo and Makoviichuk, Denys and Makoviychuk, Viktor and Liu, Zichen and Song, Yufan and Luo, Ting and Jiang, Yukun and Xu, Zhongwen and Yan, Shuicheng},
 booktitle = {Advances in Neural Information Processing Systems},
 editor = {S. Koyejo and S. Mohamed and A. Agarwal and D. Belgrave and K. Cho and A. Oh},
 pages = {22409--22421},
 publisher = {Curran Associates, Inc.},
 title = {Env{P}ool: A Highly Parallel Reinforcement Learning Environment Execution Engine},
 url = {},
 volume = {35},
 year = {2022}


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