Delay required after PUB bind before messages can be sent

[JC3]

libzmq: 4.3.5 via PyZMQ 26.2.0 (Python 3.10)
OS: macOS 13.6.6, Ubuntu 22.04

It appears that a delay is needed after creating and binding a PUB socket before the first message can be successfully published. In testing, a 200ms delay seems to be the minimum required delay. There seems to be no difference between various protocols (tried TCP and IPC). The following graph shows the send_multipart success rate vs. the delay time after bind for various delays (30 trials each).

What is going on here? Is there a more deterministic way to check if the PUB socket is ready to send rather than adding arbitrary delays?

Test Code (Python)

import zmq
import time
import multiprocessing as mp
import struct

TEST_DELAYS = range(0,251,10)
TEST_TRIALS = 30
ADDRESS = "ipc:///tmp/delay_test.ipc" # "tcp://127.0.0.1:43212"


def _sub_main (keep_running):

    ctx = zmq.Context()
    
    sub = ctx.socket(zmq.SUB)
    sub.connect(ADDRESS)
    sub.setsockopt(zmq.SUBSCRIBE, b"")
    sub.setsockopt(zmq.RCVTIMEO, 500)

    results = {}
    
    while keep_running.value:
        try:
            (delay,) = struct.unpack("<i", sub.recv_multipart()[0])
        except zmq.Again:
            continue
        results[delay] = results.get(delay, 0) + 1
        print((delay, results[delay]))

    sub.close()
    ctx.destroy()

    print("---------")
    for delay_ms, success_rate in results.items():
        print(f"{delay_ms},{success_rate/TEST_TRIALS:.3f}")


def run_test (delay):

    ctx = zmq.Context()
    pub = ctx.socket(zmq.PUB)
    pub.bind(ADDRESS)
    if delay > 0:
        time.sleep(delay/1000.0)
    pub.send_multipart([struct.pack("<i", delay)])
    pub.close()
    ctx.destroy()        

def main ():

    keep_running = mp.Value('i', 1)
    receiver = mp.Process(target=_sub_main, args=(keep_running,))
    receiver.start()

    for delay in TEST_DELAYS:
        for k in range(TEST_TRIALS):
            run_test(delay)

    keep_running.value = 0
    receiver.join()

    
if __name__ == "__main__":
    main()