Parallelize shell processes enforcing a concurrency limit using python3 and asyncio

parallelrun.py

import asyncio

concurrency_sem = asyncio.Semaphore(3)

@asyncio.coroutine
def run(process):
    yield from concurrency_sem.acquire()
    print("Running {}...".format(process))
    proc = yield from asyncio.create_subprocess_shell(process)
    yield from proc.communicate()
    print("Process {} terminated.".format(process))
    concurrency_sem.release()

tasks = [
    asyncio.Task(run("sleep 1")),
    asyncio.Task(run("sleep 2")),
    asyncio.Task(run("sleep 1")),
    asyncio.Task(run("sleep 2")),
    asyncio.Task(run("sleep 1")),
    asyncio.Task(run("sleep 2")),
    asyncio.Task(run("sleep 1")),
    asyncio.Task(run("sleep 2")),
]

loop = asyncio.get_event_loop()
loop.run_until_complete(asyncio.wait(tasks))