Implementation of get cursor position in pure Julia

[kdheepak]

Presentation.jl/src/utils.jl

Lines 51 to 76 in 07de019

	function getXY(t::Terminals.TTYTerminal)
	fd = ccall(:jl_uv_file_handle, Base.OS_HANDLE, (Ptr{Cvoid},), stdin.handle)
	systemerror("tcgetattr",
	ccall(:tcgetattr, Cint, (Cint, Ptr{Cvoid}), fd, TERM) == -1)
	systemerror("tcgetattr",
	ccall(:tcgetattr, Cint, (Cint, Ptr{Cvoid}), fd, RESTORE) == -1)
	TERM[].c_lflag &= ~(ICANON|ECHO)
	systemerror("tcsetattr",
	ccall(:tcsetattr, Cint, (Cint, Cint, Ptr{Cvoid}), fd, TCSANOW, TERM) == -1
	)
	write(stdout, "$(Terminals.CSI)6n")
	buf = UInt8[]
	while true
	ch = read(stdin, 1)[1]
	if Char(ch) == 'R'
	break
	end
	push!(buf, ch)
	end
	systemerror("tcsetattr",
	ccall(:tcsetattr, Cint, (Cint, Cint, Ptr{Cvoid}), fd, TCSANOW, RESTORE) == -1
	)
	r, c = split(String(buf[3:end]), ";")
	return parse(Int, c), parse(Int, r)
	end

[kdheepak]

@pfitzseb for your reference

[pfitzseb]

Awesome!
Two things: For that code to work on Linux it needs to be

const NCCS = Sys.islinux() ? 32 : 20
const tcflag_t = Sys.islinux() ? Cuint : Culong
const speed_t = tcflag_t
mutable struct TermIOs
  c_iflag::tcflag_t
  c_oflag::tcflag_t
  c_cflag::tcflag_t
  c_lflag::tcflag_t
  @static if Sys.islinux()
    c_line::tcflag_t
  end
  c_cc::NTuple{NCCS, UInt8}
  c_uispeed::speed_t
  c_ospeed::speed_t
end
TERM = Ref{TermIOs}(
        @static if Sys.islinux()
          TermIOs(
            0,
            0,
            0,
            0,
            0,
            Tuple([UInt8(0) for _ in 1:NCCS]),
            0,
            0
          )
        else
          TermIOs(
            0,
            0,
            0,
            0,
            Tuple([UInt8(0) for _ in 1:NCCS]),
            0,
            0
          )
        end
       )
RESTORE = deepcopy(TERM)

And unfortunately I can't use this, because it doesn't work when called in a async task:

julia> cursorpos(get_terminal())
(1, 17)

julia> @async begin 
         sleep(1)
         println("pos:")
         println(cursorpos(get_terminal()))
       end
Task (runnable) @0x00007f1ecd12e230

julia> pos:
julia> 1
1

Do you have any idea about what's going on there (or what to do about it)?

[kdheepak]

I'm getting the same behavior you are getting.

I played around with it a little. First, I'm able to run the write and read in a @async block and it works fine, which I was not expecting. It prints the stdin to the screen though.

I was then able to set the appropriate flags in the user terminal (without using the async macro), and run the cursor command (write and read) in the async macro, and reset the flags from the REPL. This kind of worked but was behaving weirdly

This led me to think that the ccall and the function is working as expected, but the while true ... if ch == "R" break is what is causing the issue.

So I changed the getXY function to the following:

    write(stdout, "$(Terminals.CSI)6n")
    buf = UInt8[]
    for _ in 1:6
        ch = read(stdin, 1)[1]
        push!(buf, ch)
    end
    ch = read(stdin, 1)[1]

Now this is what I'm getting when I run it.

The x and y are what I would have gotten if I ran it without using the @async macro.

I think the ccalls are working as expected. It's just that with @async maybe other stuff is being printed to the screen and maybe that is interfering with reading stdin (?).