aioble scan with duration_ms=0

[jef41]

When running an indefinite bluetooth scan (duration_ms=0) I seem to get a constant usage of memory that is not garbage collected. Over a period of about 24 hours this accumulates and leads to a memory error. If I run the scan in a while loop with a fixed duration (duration_ms=2000) I do not see the same issue.

I have been running this minimal sample below on a Raspberry Pi PicoW on the v1.23.0 firmware. It is difficult for me to understand but I think the indefinite scan is consuming 3 bytes per iteration of data received.

import asyncio
from aioble import central as aioble_central
from primitives import Queue
import gc

gc.collect()
gc.threshold(gc.mem_free() // 4 + gc.mem_alloc())


async def main():
    bridge_q = Queue(maxsize=16) 
    scanner = asyncio.create_task(scan_for_ibeacons(bridge_q))
    while True:
        while bridge_q.empty():
            await asyncio.sleep(1)

        if bridge_q.full(): 
            length = bridge_q.qsize()
            print("Queue is full ({} events), scans will be ignored until the queue is reduced".format(length))
        
        print(f"gc: {gc.mem_free()}\t qsize:{bridge_q.qsize()}")
        dumb_value = await bridge_q.get()
        dumb_value = None


async def scan_for_ibeacons(bridge_q):
    #iBeacon_prefix = b'\x4C\x00\x02\x15'  
    while True:
        #async with aioble_central.scan(duration_ms=2000) as scanner:
        async with aioble_central.scan(duration_ms=0) as scanner:
            async for result in scanner:
                #if result.manufacturer and result.manufacturer.startswith(IBEACON_PREFIX):
                await bridge_q.put(result.rssi)
  
   
asyncio.run(main())

It may be that I misunderstand async principles or that I misunderstand the Bluetooth library (or both). Can anyone help me to understand why this happens please? I have tried to intermittently stop and restart the indefinite scan after data is received with the code below, but that seems to make no difference, memory is still consumed;

    while True:
        async with aioble_central.scan(duration_ms=0) as scanner:
            async for result in scanner:
                #if result.manufacturer and result.manufacturer.startswith(IBEACON_PREFIX):
                await bridge_q.put(result.rssi)
                scanner.duration_ms = None

Running a fixed scan duration_ms=2000 in a while loop seems to work around the issue, but ideally I would like to understand why the minimal sample above consumes memory that is not garbage collected, or how I can track that down. Thanks!

[jef41]

for the record, the below code seems to work without eating memory, but I still don't understand why this while loop and scanner.cancel() are required when duration_ms=0;

async def scan_for_ibeacons(bridge_q):
    #iBeacon_prefix = b'\x4C\x00\x02\x15'  
    while True:
        #async with aioble_central.scan(duration_ms=2000) as scanner:
        async with aioble_central.scan(duration_ms=0) as scanner:
            async for result in scanner:
                #if result.manufacturer and result.manufacturer.startswith(IBEACON_PREFIX):
                await bridge_q.put(result.rssi)
            scanner.cancel()