Ray actors are used to parallelize a class instance to perform stateful operations in parallel. Ray will start a remote instance of the class and then execute remote method calls and maintain its own internal state. The example below compares a parallel Ray actor approach to a standard class approach. A computationally expensive task is simulated by using the sleep() function.
import ray
import time
@ray.remote
class Counter:
def __init__(self):
self.n = 0
def increment(self):
time.sleep(1)
self.n += 1
def read(self):
return self.n
class Counter2:
def __init__(self):
self.n = 0
def increment(self):
time.sleep(1)
self.n += 1
def read(self):
return self.n
def run_ray():
"""
Execute a Ray actor model in parallel. Compared elapsed time to the
non-parallel example `run_noray()`.
"""
ray.init()
tic = time.perf_counter()
counters = [Counter.remote() for i in range(4)]
[c.increment.remote() for c in counters]
[c.increment.remote() for c in counters]
futures = [c.read.remote() for c in counters]
values = ray.get(futures)
toc = time.perf_counter()
print(f'Elapsed time {toc - tic:.2f} s')
print(values)
ray.shutdown()
def run_noray():
"""
Excecute several class instances in series, not parallel. Compare elapsed
time to the Ray parallel example `run_ray()`.
"""
tic = time.perf_counter()
counters = [Counter2() for _ in range(4)]
[c.increment() for c in counters]
[c.increment() for c in counters]
values = [c.read() for c in counters]
toc = time.perf_counter()
print(f'Elapsed time {toc - tic:.2f} s')
print(values)
def main():
"""
Run the Ray example or the non-Ray example.
"""
# run_ray()
run_noray()
if __name__ == '__main__':
main()
Results from running the above example on a 6-core MacBook Pro are shown below. As expected, the example that uses the parallel Ray actor has the fastest elapsed time.
# Results from running the parallel Ray actor
Elapsed time 3.28 s
[2, 2, 2, 2]
# Results from running the non-parallel class approach
Elapsed time 8.02 s
[2, 2, 2, 2]
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