bleak: MacOS: scanning in new thread raises BleakError("Bluetooth device is turned off")

• bleak version: 0.6.4
• Python version: 3.8.2
• Operating System: MacOS 10.15.4

Trying to do scanning in a new thread raises BleakError("Bluetooth device is turned off"). Run the program below with and without --thread. In the latter case, the error is raised, but the program works fine with everything in the same thread.

Using BleakScanner rather than discover has the same problem.

This program runs fine on Linux with BlueZ, and on Windows 10 with Python 3.7.7 and pythonnet.

This sounds sort of like #93 and #125, but those were BlueZ problems. This stackoverflow Q&A may also be of interest, though I don’t know corebluetooth well enough to confirm: https://stackoverflow.com/questions/48958267/how-can-i-use-corebluetooth-for-python-without-giving-up-the-main-thread

The reason I’m using a second thread is that I’m re-implementing an existing non-async BLE API using bleak. I was using a fresh thread for the bleak async side of things, and a janus queue to pass back scanning results.

import asyncio
from bleak import discover
from threading import Thread
import argparse

parser = argparse.ArgumentParser()
parser.add_argument('--thread', action='store_true')
args = parser.parse_args()

async def scan():
    devices = await discover()
    for d in devices:
        print(d)

def run():
    asyncio.run(scan(), debug=True)

if args.thread:
    print("in separate thread")
    t = Thread(target=run)
    t.start()
    t.join()
else:
    print("in main thread")
    loop = asyncio.get_event_loop()
    loop.run_until_complete(scan())