Ray supports running distributed python programs with the multiprocessing.Pool API
using Ray Actors instead of local processes. This makes it easy
to scale existing applications that use
multiprocessing.Pool from a single node
to a cluster.
To get started, first install Ray, then use
ray.util.multiprocessing.Pool in place of
This will start a local Ray cluster the first time you create a
distribute your tasks across it. See the Run on a Cluster section below for
instructions to run on a multi-node Ray cluster instead.
from ray.util.multiprocessing import Pool def f(index): return index pool = Pool() for result in pool.map(f, range(100)): print(result)
multiprocessing.Pool API is currently supported. Please see the
multiprocessing documentation for details.
context argument in the
Pool constructor is ignored when using Ray.
Run on a Cluster¶
This section assumes that you have a running Ray cluster. To start a Ray cluster, please refer to the cluster setup instructions.
To connect a
Pool to a running Ray cluster, you can specify the address of the
head node in one of two ways:
By setting the
By passing the
ray_addresskeyword argument to the
from ray.util.multiprocessing import Pool # Starts a new local Ray cluster. pool = Pool() # Connects to a running Ray cluster, with the current node as the head node. # Alternatively, set the environment variable RAY_ADDRESS="auto". pool = Pool(ray_address="auto") # Connects to a running Ray cluster, with a remote node as the head node. # Alternatively, set the environment variable RAY_ADDRESS="<ip_address>:<port>". pool = Pool(ray_address="<ip_address>:<port>")
You can also start Ray manually by calling
ray.init() (with any of its supported
configuration options) before creating a