The USB pending transfer flag was cleared before calling the completion
callback, to allow the callback code to call submit_xfer() again.
Unfortunately this isn't safe in a multi-threaded environment, as another
thread may see the endpoint is available before the callback is done
executing and submit a new transfer.
Rather than adding extra locking, specifically treat the transfer as still
pending if checked from another thread while the callback is executing.
Closes#874
Signed-off-by: Angus Gratton <angus@redyak.com.au>
These packages build on top of machine.USBDevice() to provide high level
and flexible support for implementing USB devices in Python code.
Additional credits, as per included copyright notices:
- CDC support based on initial implementation by @hoihu with fixes by
@linted.
- MIDI support based on initial implementation by @paulhamsh.
- HID keypad example based on work by @turmoni.
- Everyone who tested and provided feedback on early versions of these
packages.
This work was funded through GitHub Sponsors.
Signed-off-by: Angus Gratton <angus@redyak.com.au>
Angus Gratton