Bulkhead Thread Pool per Service Mock in Python

import threading
import time
import random
from concurrent.futures import ThreadPoolExecutor

class ServiceBulkhead:
    def __init__(self, name, max_threads, max_queue):
        self.name = name
        self.executor = ThreadPoolExecutor(max_workers=max_threads)
        self.semaphore = threading.Semaphore(max_threads + max_queue)
        self.active = 0
        self.lock = threading.Lock()

    def call(self, fn, *args, **kwargs):
        if not self.semaphore.acquire(blocking=False):
            print(f"{self.name}: REJECTED - bulkhead full")
            return None
        try:
            with self.lock:
                self.active += 1
            result = self.executor.submit(fn, *args, **kwargs).result()
            return result
        finally:
            with self.lock:
                self.active -= 1
            self.semaphore.release()


def mock_service_call(service_name, delay):
    time.sleep(delay)
    return f"{service_name} response after {delay:.1f}s"


if __name__ == "__main__":
    payment = ServiceBulkhead("payment", max_threads=2, max_queue=2)
    shipping = ServiceBulkhead("shipping", max_threads=1, max_queue=1)

    def send_to_service(bulkhead, service):
        print(f"Sending to {service}...")
        result = bulkhead.call(mock_service_call, service, random.uniform(0.2, 0.8))
        if result:
            print(f"Result: {result}")

    threads = []
    for i in range(5):
        threads.append(threading.Thread(target=send_to_service, args=(payment, "payment")))
    for i in range(3):
        threads.append(threading.Thread(target=send_to_service, args=(shipping, "shipping")))

    for t in threads:
        t.start()
    for t in threads:
        t.join()