is possible to implement non blocking wlan scan (especially on esp32 port)?

[puppet13th]

Hello everybody.
currently sta.scan is blocking function, is it possible to implement it non blocking ways like sta.connect?

[stephanelsmith]

I don't think so. I would personally love to see callbacks on every scan result, similar to the bluetooth IRQ callback system. Which could then be wrapped into an asyncio system.

[puppet13th]

That one will be nice too, can incorporate asyncio to handle scan result.
Eg like polling scan for known wlan ssid, and connect known network when in range( show up in scan result)

[jonathanhogg]

I'm a bit late to this question, but in case it's still useful to you (or useful to someone else) I wrap the .scan() method in a thread and that works fine on ESP32.

Adapted excerpt from my code:

class WifiManager:
    def __init__(self):
        self.wlan = network.WLAN(network.STA_IF)
        self.wlan.active(True)
        self._scan_start = _thread.allocate_lock()
        self._scan_start.acquire()
        self._scan_complete = asyncio.ThreadSafeFlag()
        self._scan_thread = _thread.start_new_thread(self._scan, ())
        self._scan_results = None

    def _scan(self):
        while True:
            self._scan_start.acquire()
            try:
                self._scan_results = self.wlan.scan()
            except Exception as exc:
                Log.warning("Exception running scan", exc=exc)
                self._scan_results = []
            self._scan_complete.set()

    async def scan(self):
        self._scan_start.release()
        await self._scan_complete.wait()
        self._scan_complete.clear()
        return self._scan_results

I keep one, long-running background thread to look after scans. This thread is woken up by releasing a _thread.Lock and then notifies it is finished via an asyncio.ThreadSafeFlag so that the scan results can be awaited.

[puppet13th]

@jonathanhogg thank your for your reply. does other coro/task still running while waiting for scan result?

[jonathanhogg]

Yes. The await self._scan_complete.wait() explicitly hands control back to the asyncio scheduler until the scan, which is running on a background thread, has completed.

This approach has been rock solid for me, though I would certainly try to avoid touching the network.WLAN() object in any other way while the scan is running in case.

[stephanelsmith]

Wow, just seeing this again, incredible, can't way to try it. Thank you for the tip. I hadn't considered using threads. bump