Control flushing to stdout... core.osthread.Thread + arsd.terminal

[Adam D. Ruppe]

On Friday, 5 June 2020 at 20:11:16 UTC, aberba wrote:
> Didn't come to mind to lookup from terminal docs. Thought it 
> was a Dlang/OS problem.

Yeah, the OS by itself rarely buffers output like this, but both 
the C library (on which std.stdio is built) and my Terminal 
object do (they do separately btw, which is why I suggest you 
avoid mixing together terminal.writeln and regular 
stdout.writeln, since they can intermix unpredictably as they 
flush at different calls).

The C one tends to auto-flush on newline, unless it is piped to 
another program... which confuses poor users on IDEs, since from 
the program's perspective, the IDE console is another program! So 
your output can be delayed differently there vs direct to the 
user's screen. (My terminal.d will actually throw an exception if 
you try to use it in such an environment. You need to check 
Terminal.stdoutIsTerminal() if you want to handle that case 
differently. This is another decision I semi-regret and might 
change in the future, since a lot of things do work fine in that 
environment, you just can't move the cursor around in it.)

Anyway the point is just that output functions often pretend to 
succeed while actually just buffering it internally. Unless the 
docs say otherwise when using one of these, there's no guarantee 
it will actually display until you call the library's flush 
function (in std.stdio btw it is `stdout.flush();`, in C it is 
`fflush(stdio);`) or close the file.