bytesavailable wrong when piping input

[Seelengrab]

MWE:

[sukera@tower ~]$ cat example.jl 
function foo()
    while iszero(bytesavailable(stdin))
        println("no data")
        sleep(0.2)
    end
    write(stdout, readavailable(stdin))
    println()
end
[sukera@tower ~]$ echo "foo" | julia -L example.jl -e 'foo()'
no data
no data
no data
no data
no data
no data
no data
^C

This should just print foo\n on stdout and then exit, since there clearly is data available.

[KristofferC]

Ref #14624 (comment)

[Seelengrab]

Right, I keep forgetting that our async I/O is actually synchronous under the hood and that we only start to buffer once you try to read.......