"Manually using a lock is a smell in the same way that goto is a smell."

The presence of a lock tells you nothing about whether a program is well-designed. In fact, the whole idea that you can argue about the correctness of a program from the presence or absence of "code smells" is absurdly simplistic. I have seen plenty of bad code littered with while statements.

There isn't really that big of a difference between a lock and a wait, which is the point that was being made. It either way will "lock" up the thread until condition X is full filled and since it depends on other threads to finish, it's still very possible to get deadlocks and a like.

Besides that, depending on the task, it's very important how something is implemented.

And if both threads are doing a blocking read waiting for their message? Blocking locks, deadlocks, endless fun...

But wait, you don't use blocking-IO, you poll the sockets to see if there is data available, right? Do you realize what you are polling? (hint, it is global and mutable)