Use unsafe for most of the FFI

[thumphries]

... except the stuff that uses FunPtr.

Important for throughput, but would like to have real tests before doing so

[nh2]

Wait, don't the C calls block (because they do networking)?

One must not use unsafe for anything that is not "instantantaneous" (that is, does only CPU-bound activity), because it blocks the entire CPU core (so you can have at maximum N unsafe operations at once for the N given in +RTS -N).

See haskell/unix#34 for more details.

[thumphries]

Most of this API is asynchronous, network IO is handled by a separate thread and the C bindings just throw requests onto a queue

[thumphries]

I do, however, frequently get confused between safe and unsafe. To rephrase the issue, "maximise concurrent throughput any way possible"