Thread by @danluu

I think I failed an interview at FB a long time ago (~2013) because of this.

The interviewer asked me how you can write deadlock free code, and I told him that there's this thing people say about taking/releasing locks in order, but there are places where that won't save you.

https://twitter.com/rygorous/status/1446983617465307137

The interviewer didn't like that answer and said, about other circumstances, "there's got to be a way".

I discussed some places where that isn't sufficient, e.g., in processor hardware and microcode, where you wouldn't do that for performance reasons even if you could and

of course that's where you implement the primitives that other people will be able to take locks and you can't use the primitive you're creating to implement the primitive itself.

But still, the interviewer insisted "there's got to be a way"

I also gave the meta argument that CPUs have deadlock and livelock detection logic that, when it detects one, effectively randomly perturbs the state in the hopes of putting processor into a good state, which isn't something people would do if there was a better known solution.

But the interviewer continued to insist "there's got to be a way" and seemed to think I was a bozo since I was writing concurrent code without knowing how to guarantee that the code wouldn't deadlock.

Anyway, I failed that interview!

But, on the bright side, at least I didn't miss out on tens of millions of dollars of equity even though I passed the technical interview because I said "hoops".

https://twitter.com/danluu/status/925919331933937664