stateful-pool 0.3.1

A process pool that allows workers to maintain state across tasks.

Default ProcessPoolExecutor makes it hard to maintain stateful workers, especially workers with expensive setup (e.g., workers each with a model loaded in GPU memory).

This library lets you create a pool of stateful workers (spawn once) to run tasks in parallel across processes (execute many).

+-----------------------+              +----------------------+
|     Main Process      |              |     Process Pool     |
| +--------+ +--------+ |              | +------------------+ |
| | Thread | | Thread | | --- Task --> | | Worker (Process) | |
| |   1    | |   2    | | <-- Resp --- | +------------------+ |
| +--------+ +--------+ |              | +------------------+ |
|      ...     ...      |              | | Worker (Process) | |
| +--------+ +--------+ |              | +------------------+ |
| | Thread | | Thread | | --- Task --> |         ...          |
| |  N-1   | |   N    | | <-- Resp --- | +------------------+ |
| +--------+ +--------+ |              | | Worker (Process) | |
|                       |              | +------------------+ |
+-----------------------+              +----------------------+

Installation:

pip install stateful-pool

Following is an example of how to define a worker class, spawn workers (each assigned several GPU IDs), and execute tasks on them.

from stateful_pool import SPool, SWorker
import time, random

# will run in another process
class SquareWorker(SWorker):
    gpu_ids: list[int]

    def spawn(self, gpu_ids: list[int]):
        self.gpu_ids = gpu_ids
        return f"Worker initialized on GPU: {self.gpu_ids}"
    
    def execute(self, value):
        time.sleep(random.uniform(0.1, 1.0))
        return f"[Execute] Square of {value} is {value * value} (computed on GPU: {self.gpu_ids})"

if __name__ == "__main__":

    with SPool(SquareWorker, queue_size=100) as pool:
        # spawn a worker, return value can be captured
        s = pool.spawn(gpu_ids=[0, 1])
        print(f"{s}")

        # submit a single task and wait for result
        r = pool.execute(100)
        print(r)

The example calls pool.execute once. This doesn't demonstrate the power of the pool (parallelism). In practice, you would likely want to submit tasks in a non-blocking manner via submit_* counterparts:

with SPool(SquareWorker) as pool:
    spawn_futures = [pool.submit_spawn(gpu_ids=[i, i+1]) for i in range(0, 4, 2)]
    for f in spawn_futures:
        print(f.result())
    
    execute_futures = [pool.submit_execute(i) for i in range(4)]
    for f in execute_futures:
        print(f.result())