flush.console() does not seem to work

[gaborcsardi]

System details

RStudio Edition : desktop
RStudio Version : 1.4.867
OS Version      : macOS 10.14.6
R Version       : 4.0.2

Steps to reproduce the problem

RUn this:

fun <- function() { 
  cat("select the file in the dialog box\n")
  flush.console()
  file.choose()
}
fun()

Describe the problem in detail

flush.console() is supposed to flush the console buffer, so the in the code above the cat()-ed text should appear, before the file.choose() dialog appears.

Describe the behavior you expected

I expected the cat()-ed text to appear in the console before the file chooser dialog.

• I have read the guide for submitting good bug reports.
• I have installed the latest version of RStudio, and confirmed that the issue still persists.
• If I am reporting a RStudio crash, I have included a diagnostics report.
• I have done my best to include a minimal, self-contained set of instructions for consistently reproducing the issue.

[adamconroy]

I am not able to reproduce this, at least in the two environments I tried. @ronblum have you ever seen what he's describing?

[kevinushey]

Reproduces for me:

Note fun() called in the console but no other console output available.

That said, we explicitly don't hook into R_FlushConsole() and friends:

rstudio/src/cpp/r/session/REmbeddedPosix.cpp

Lines 151 to 155 in 06503e5

	// NOTE: we do not hook the following callbacks because they are targeted
	// at clients that have a stdio-based console
	// ptr_R_ResetConsole
	// ptr_R_FlushConsole
	// ptr_R_ClearerrConsole

but it seems like it would be reasonable to use those so that we could synchronize on any pending console text that needs to be rendered in the browser.

All that said... definitely not for 1.4! An appropriate workaround here would be something like:

if (identical(.Platform$GUI, "RStudio"))
      Sys.sleep(0.1)

after calling flush.console().

[gaborcsardi]

Does Sys.sleep(0.1) ensure that the output is printed? How low can you go?

[kevinushey]

Good question -- I'm not sure, and this is definitely a hack that might fail 0.1% of the time :-)

[gaborcsardi]

Yeah, it is not really worth it then, I would say. It would be great to fix, if not in 1.4, then later, because RGui and R.app both support this.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs, per https://github.com/rstudio/rstudio/wiki/Issue-Grooming. Thank you for your contributions.

[gaborcsardi]

This is still an issue, please don't close it.