Likewise. In one interview, I was given a short task to write some simple multithreaded C++ application before the interview. IIRC it was just a bunch of time

Likewise. In one interview, I was given a short task to write some simple multithreaded C++ application before the interview. IIRC it was just a bunch of timers running in parallel to trigger events. During the onsite, they said here's the code you gave us, now here's a laptop, make it a client/server system in the next couple of hours. The time pressure didn't hurt. Had to remind myself about the order of all the necessary system calls on the client and server side to set up the sockets, listen and connect, define a suitable message format, and whatnot. But I had a working client and server talking to each other doing their thing. What I like about this style of interview is that it demonstrates your ability to be given a high-level problem and then go through requirements, design, implementation, testing then when given new requirements, iterate over the process to meet them. It's much more representative of day to day job requirements than a whiteboard. And being thrown that challenge shortly after coming onsite demonstrates that you can handle the pressure of being given new requirements and new tasks out of the blue and roll with it.