util/agents/usb_hid_relay: fix concurrent access #1526
Merged
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Since c9fc5bf, it was no longer possible to use the same USB relay device from multiple labgrid processes, as the USB device was kept open and claimed.
To fix this, we use a context manager which first claims the USB interface (with retry while busy) and releases it after the transaction.
With this fix, multiple processes can toggle outputs in a busy loop without causing 'USBError(16, 'Resource busy')' failures.
Fixes: c9fc5bf ("labgrid/util/agents/usb_hid_relay: keep the USB device open")