Multiprocessing API

Lithops implements Python’s multiprocessing API to transparently run local-parallel applications but using serverless functions for Processes and a Redis instance for shared state and Inter-Process Communication (IPC).

Process and Pool

Processes and Pool are the abstractions used in multiprocessing to parallelize computation. They interact directly with Lithop’s Futures API.

# from multiprocessing import Process
from lithops.multiprocessing import Process


def my_process_function(name):
    print(f'Hello {name}!)

p = Process(target=my_process_function, args=('World',))
p.start()
p.join()
# from multiprocessing import Pool
from lithops.multiprocessing import Pool

def square(x):
    return x * x

with Pool() as pool:
    async_result = pool.map_async(square, [1, 2, 3, 4, 5])
    try:
        result = async_result.get(timeout=3)
        print(result)
    except TimeoutError:
        print("Timed out!")

Stateful abstractions

Lithops also implements all stateful abstractions from Python mutliprocessing: Queue, Pipes, Shared memory, Events…

Since FaaS lacks mechanisms for function-to-function communication, a Redis database instance node is used.

Note

Both the functions and the Lithops orchestrator local process must be able to access the Redis instance – for example, deploying it in your local machine won’t work

The Redis credentials (host, password…) is loaded from the redis section of the Lithops configuration.

The fastest way to deploy a Redis instance is using Docker in a VM located in the cloud of your choice:

$ docker run --rm -d --network host --name redis redis:6.2.1 --requirepass redispassword

To have lower latency, you can deploy the functions and the VM in the same VPC and use route through internal traffic instead of the internet. For example, in AWS, the functions and VM can be deployed in the same VPC: Lambdas go to a private subnet and the VM in a public subnet. This way, the VM has access to the internet and the local Lithops process can also access it.

Extra multiprocessing configuration

The Lithops multiprocessing module has extra configuration specific to the multiprocessing functionality. To preserve transparency, the functions and method signature has remain completely compatible with the original multiprocessing module. For this reason, to set specific configuration in runtime, the Lithops.multiprocessing.config module is used:

import lithops.multiprocessing as mp
from lithops.multiprocessing import config as mp_config


def my_map_function(x):
    return x + 7


if __name__ == "__main__":
    iterdata = [1, 2, 3, 4]

    # To set a config parameter, use the set_parameter
    # function and specify the parameter and the desired value
    mp_config.set_parameter(mp_config.LITHOPS_CONFIG, {'lithops': {'mode': 'localhost'}})
    mp_config.set_parameter(mp_config.STREAM_STDOUT, True)
    mp_config.set_parameter(mp_config.REDIS_EXPIRY_TIME, 1800)
    mp_config.set_parameter(mp_config.PIPE_CONNECTION_TYPE, 'redislist')
    mp_config.set_parameter(mp_config.ENV_VARS, {'ENVVAR': 'hello'})
    mp_config.set_parameter(mp_config.EXPORT_EXECUTION_DETAILS, '.')

    with mp.Pool() as pool:
        results = pool.map(my_map_function, iterdata)

    print(results)

Multiprocessing configuration keys

Key

Description

Default

LITHOPS_CONFIG

Lithops configuration, passed directly to Lithop’s FunctionExecutor

{}

STREAM_STDOUT

Stream processes STDOUT to the local terminal through Redis pubsub

False

REDIS_EXPIRY_TIME

Expiry time for used Redis keys

3600 (1 hour)

PIPE_CONNECTION_TYPE

Connection type for the Pipe abstraction, can be redislist for using Redis or nanomsg for function-to-function direct communication using NanoMSG*

redislist

ENV_VARS

Environment variables for the processes, passed directly to Lithops FunctionExecutor extra_env argument

{}

EXPORT_EXECUTION_DETAILS

Calls lithops.FunctionExecutor.plot(), pass a path to store the plots, None to disable it

None

  • To use nanomsg for Pipes, you must still deploy a Redis instance (used for pipe directory). Note that this feature only works in environments where functions can open a port and communicate with each other.