How do I wait for ray on Actor class?

I am developing Actor class and ray.wait() to collect the results.

Below is the code and console outputs which is collecting the result for only 2 Actors when there are 3 Actors.

import time
import ray


@ray.remote
class Tester:
    def __init__(self, param):
        self.param = param

    def run(self):
        return self.param

params = [0,1,2]
testers = []
for p in params:
    tester = Tester.remote(p)
    testers.append(tester)

runs = []
for i, tester in enumerate(testers):
    runs.append(tester.run.remote())

while len(runs):
    done_id, result_ids = ray.wait(runs)
    #runs size is not decreasing

    result = ray.get(done_id[0])
    print('result:{}'.format(result))
    time.sleep(1)

result:2
(pid=819202) 
(pid=819200) 
(pid=819198) 
result:1
result:0
result:0
result:0
result:0
result:0
...
...
...

The console is printing out forever because the runs variable's size is not reduced.

When I call ray.wait(runs) and get the done_id, runs's element with the done_id should be removed, but it is not removed.

I want the console output to be like below.

result:2
(pid=819202) 
(pid=819200) 
(pid=819198) 
result:1
result:0

Solution

The script you provided is using ray.wait incorrectly. The following code does what you want:

import time
import ray

@ray.remote
class Tester:
    def __init__(self, param):
        self.param = param

    def run(self):
        return self.param

params = [0, 1, 2]

# I use list comprehensions instead of for loops for terseness.
testers = [Tester.remote(p) for p in params]
not_done_ids = [tester.run.remote() for tester in testers]

# len() is not required to check that the list is empty.
while not_done_ids:
    
    # Replace not_done_ids with the list of object references that aren't
    # ready. Store the list of object references that are ready in done_ids.
    # timeout=1 means sleep at most 1 second, do not sleep if there are
    # new object references that are ready.
    done_ids, not_done_ids = ray.wait(not_done_ids, timeout=1)
    
    # ray.get can take an iterable of object references.
    done_return_values = ray.get(done_ids)

    # Process each result.
    for result in done_return_values:
        print(f'result: {result}')

I added the following fixes:

ray.wait returns two lists, a list of objects that are ready, and a list of objects that may or may not be ready. You should iterate over the first list to get all object references that are ready.
Your while loop goes forever until the list is empty. I simply replaced the runs list with not_done_ids so that once all object references are ready, the while loop breaks.
ray.wait supports sleeping, with timeout. I removed your sleep and added timeout=1, which enables the program to run more efficiently (there is no sleep if another object is ready!).