AsyncIO / Concurrency for Actors¶
Within a single actor process, it is possible to execute concurrent threads.
Ray offers two types of concurrency within an actor:
Keep in mind that the Python’s Global Interpreter Lock (GIL) will only allow one thread of Python code running at once.
This means if you are just parallelizing Python code, you won’t get true parallelism. If you calls Numpy, Cython, Tensorflow, or PyTorch code, these libraries will release the GIL when calling into C/C++ functions.
AsyncIO for Actors¶
Since Python 3.5, it is possible to write concurrent code using the
Ray natively integrates with asyncio. You can use ray alongside with popular
async frameworks like aiohttp, aioredis, etc.
You can try it about by running the following snippet in
ipython or a shell
that supports top level
import ray import asyncio ray.init() @ray.remote class AsyncActor: # multiple invocation of this method can be running in # the event loop at the same time async def run_concurrent(self): print("started") await asyncio.sleep(2) # concurrent workload here print("finished") actor = AsyncActor.remote() # regular ray.get ray.get([actor.run_concurrent.remote() for _ in range(4)]) # async ray.get await actor.run_concurrent.remote()
ObjectRefs as asyncio.Futures¶
ObjectRefs can be translated to asyncio.Futures. This feature
make it possible to
await on ray futures in existing concurrent
@ray.remote def some_task(): return 1 ray.get(some_task.remote()) ray.wait([some_task.remote()])
you can do:
@ray.remote def some_task(): return 1 await some_task.remote() await asyncio.wait([some_task.remote()])
Please refer to asyncio doc
for more asyncio patterns including timeouts and
Defining an Async Actor¶
By using async method definitions, Ray will automatically detect whether an actor support async calls or not.
import asyncio @ray.remote class AsyncActor: async def run_task(self): print("started") await asyncio.sleep(1) # Network, I/O task here print("ended") actor = AsyncActor.remote() # All 50 tasks should start at once. After 1 second they should all finish. # they should finish at the same time ray.get([actor.run_task.remote() for _ in range(50)])
Under the hood, Ray runs all of the methods inside a single python event loop.
Please note that running blocking
ray.wait inside async
actor method is not allowed, because
ray.get will block the execution
of the event loop.
In async actors, only one task can be running at any point in time (though tasks can be multi-plexed). There will be only one thread in AsyncActor! See Threaded Actors if you want a threadpool.
Setting concurrency in Async Actors¶
You can set the number of “concurrent” task running at once using the
max_concurrency flag. By default, 1000 tasks can be running concurrently.
import asyncio @ray.remote class AsyncActor: async def run_task(self): print("started") await asyncio.sleep(1) # Network, I/O task here print("ended") actor = AsyncActor.options(max_concurrency=10).remote() # Only 10 tasks will be running concurrently. Once 10 finish, the next 10 should run. ray.get([actor.run_task.remote() for _ in range(50)])
Sometimes, asyncio is not an ideal solution for your actor. For example, you may
have one method that performs some computation heavy task while blocking the event loop, not giving up control via
await. This would hurt the performance of an Async Actor because Async Actors can only execute 1 task at a time and rely on
await to context switch.
Instead, you can use the
max_concurrency Actor options without any async methods, allowng you to achieve threaded concurrency (like a thread pool).
When there is at least one
async def method in actor definition, Ray
will recognize the actor as AsyncActor instead of ThreadedActor.
@ray.remote class ThreadedActor: def task_1(self): print("I'm running in a thread!") def task_2(self): print("I'm running in another thread!") a = ThreadedActor.options(max_concurrency=2).remote() ray.get([a.task_1.remote(), a.task_2.remote()])
Each invocation of the threaded actor will be running in a thread pool. The size of the threadpool is limited by the