[cycloptic]

>If you're expecting a blocking system call, and actually get a brand new background thread that's polling, it's quite reasonable to be frustrated.

It really isn't if the documentation doesn't outright say that it's single threaded and not thread safe. For a lot of simpler use cases where you just want to ship a thread-safe API (e.g. application does not have its own thread pool) then it just makes sense in a lot of cases to use some kind of automatic thread pooling. The caller does not have to know or care how the internal state machine is implemented.

If you have implemented your own thread pool it seems you should know enough to dig down enough to the lower layers to where you can get to that blocking syscall, or least to the point where you can strip off the O_NONBLOCK flags yourself.