How to specify Device Interface # at connection/open?

[drfrankencopter]

Total USB newb here. I'm trying to connect to a device (Grayhill touch encoder) that has 2 Interfaces. I can see them both clearly identified when hid_enumerate() runs through them. But where I'm confused is how to specify which interface I'm connecting to with a hid_open() command. It seems here I can only specify the Vendor, Product, and SerNo...but can't specify the interface itself.

Should I be using hid_open_path(), and pulling the specific path the interface from the device_info struct I get from HID enumerate? I'm guessing this is the case, but if anyone can confirm that would be greatly appreciated.

Oh, and FWIW I'm attempting to use hidapi in a multi-threaded sense, so I can separate my device reads from the writes. I see in some of the issues pages that the api isn't really thread safe, so if there's a place to go for some guidance on what not to do in multi-threaded applications that would also be helpful. Or, alternatively if there's a place to go to get some basic info on a suitable program flow for reading device reports, and writing reports please point me at it.

Thanks for all the work on this API!

[Youw]

Should I be using hid_open_path(), and pulling the specific path the interface from the device_info struct I get from HID enumerate? I'm guessing this is the case, but if anyone can confirm that would be greatly appreciated.

That is correct.

some guidance on what not to do in multi-threaded applications that would also be helpful

• Always syncronize enumeration/open/close of the device(s);
• Always syncronize device-specific function calls (per-device);
• hid_read is the only function that can be used asyncronous from other device-specific functions;

There're still some issues in some corner cases, but that is the best working solution as of right now.

[drfrankencopter]

Thanks for the quick, and clear answer!