[WIP] Begin implementation of asynchronous transfers, Issue #63

[mrnuke]

The purpose of these patches is to allow asynchronous USB transfers. Keep in mind that I am not claiming this should be the final form. I'm not an asyncio expert, and I am open for suggestions on how to improve the implementation. Note that async transfers are only imlemented for the libusb1 backend.
I am striving to achieve an API that looks like the following example:

async def do_usb_stuff():
    dev = usb.core.find(...)

    transfer1 = dev.submit_read(...)
    transfer2 = dev.submit_write(...)

    await transfer2.result()
    await transfer1.result()

Note that this is symmetrical to the sync functions, in that the transfer type does not have to be specified. It is derived from the endpoint.

await transfer.result() is similar to an asyncio.Future, although the implementation is not exactly an awaitable future. This is an implementation detail, and it could be changed if needed.

[mcuee]

https://github.com/vpelletier/python-libusb1
Not so sure if the implementation in python-libusb1 is of some reference value here.

[mcuee]

This is a WIP to address #63.

[WhiteApfel]

Nope 😕 I tried to test on my receipt printer:

from escpos.printer import Usb

p = Usb(0x2730, 0x2002, None, 0, 0x81, 0x02)
print("#print text")
p.text(f"{'ПУТИН ХУЙЛО ' * 300}")
print("#print qr")
p.qr("All the things she said", size=16, model=2)
print("#cut")
p.cut(feed=False)

Changed the function to show execution time:

        import time
        while not self._fut.done():
            st = time.time()
            _check(_lib.libusb_handle_events(self._ctx))
            print(round(time.time()-st, 5))
            await asyncio.sleep(0.0001)

#print text
4e-05
0.00304
#print qr
2e-05
1.71189
1e-05
1e-05
#cut
2e-05

[mcuee]

Not sure if anyone is working on this or not. I tend to think this is one major missing feature (along with hotplug).