I applied at a career fair and then took an online assessment. Later, I had a half-hour technical phone interview, after which I was told they wanted to interview me on-site.

There, I spoke with HR and a few developers. With HR, I discussed myself and basic topics like past projects. Then it was time for the developer interviews. The first interviewer asked a couple of software questions, which weren't difficult and I answered them fine. The other interviewers asked very hardware-related questions, which I wasn't expecting at all (though I admit I should have known).

Overall, the entire process felt very rushed. I traveled there in the morning, underwent a quick three-hour interview, and was then dismissed in the afternoon. The interview's midpoint was just about noon, and they provided no food the entire time (although one developer mentioned that if I didn't have any other questions, he was going to end the interview early to get lunch!). I received a bad vibe from them, which was in contrast to how well similar companies in the area/field treat interviewees.

Why might multiple threads calling a simple function involving array access or possible modification be much slower than a single thread calling the same function?