`Timer` is ~1ms too slow

[jakobnissen]

On my computer, Timer is about one millisecond too slow:
E.g:

julia> @btime sleep(0.001)
  2.062 ms (4 allocations: 112 bytes)

This also reproduces in more realistic scenarios where I'm timing a loop which can be assumed to be dominated by sleep.

The code for Timer states:

# libuv has a tendency to timeout 1 ms early, so we need +1 on the timeout (in milliseconds), unless it is zero

Maybe this was fixed in libuv?

[ufechner7]

Use:

function nonblocking_systemsleep(t)
   task = Threads.@spawn Libc.systemsleep($t)
   yield()
   fetch(task)
end

Or look at: https://github.com/ufechner7/Timers.jl

But this all depends on the OS you use, only Linux allows non-blocking sleep with less than 1ms.