tcltk causes help() to hang in R 4.2.0 on macOS

For reference, this problem is not macOS specific, it also exists on 
Linux (but not on Windows which use a different code path) and the core 
problem is how to prevent re-entrant execution of R event handlers when 
run from the R/tcltk event loop, itself running from an R event handler.

R-patched now contains a defensive work-around from Simon.

We have added a more efficient and cleaner fix to R-devel, but there is 
some risk of breakage: this form is "the documented way" but didn't work 
on some systems ~22 years ago. So it would be great if people using 
Tcl/Tk in R on Unix, and particularly those with rarely used window 
managers, could test their applications or the tcltk package demos and 
report any issues well before the next release.

Thanks
Tomas

On 5/30/22 01:27, John Fox wrote:

Dear Simon,

Thank you for addressing this problem so promptly.

Best,
?John

On 2022-05-29 6:51 p.m., Simon Urbanek wrote:

Actually, I take back the reference to the commit - the deadlock is 
true, and removing the line is a work-around, but r78421 was not 
necessarily the regression. The issue seems to be caused by a 
combination of Tcl/Tk and KaTeX (the latter causes the browser to 
issue multiple parallel http-requests and the former causes the 
deadlock in its event loop) which has not been there in earlier R 
versions.

Cheers,
Simon

On 30/05/2022, at 10:09 AM, Simon Urbanek 
<simon.urbanek at r-project.org> wrote:

John,

thanks, this is a regression caused by r78421 (deadlock when TclTk's 
event loop is called in http processing). Removing L875 in 
src/modules/internet/Rhttpd.c restores the previous behavior, but 
the underlying problem is more complex and will require more 
investigation.

Cheers,
Simon

On 29/05/2022, at 5:36 AM, John Fox <jfox at mcmaster.ca> wrote:

Dear R-sig-mac list members,

I've discovered that loading the tcltk package apparently causes R 
4.2.0 (including the current patched version) to hang on an M1 Mac.

Try, e.g.,

library("tcltk")
help("lm")

My session info:

------- snip -------

sessionInfo()

R version 4.2.0 Patched (2022-05-28 r82413)
Platform: aarch64-apple-darwin20 (64-bit)
Running under: macOS Monterey 12.3.1

Matrix products: default
BLAS: 
/Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/lib/libRblas.0.dylib 

LAPACK: 
/Library/Frameworks/R.framework/Versions/4.2-arm64/Resources/lib/libRlapack.dylib 


locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8

attached base packages:
[1] tcltk???? stats???? graphics? grDevices utils datasets? methods
[8] base

loaded via a namespace (and not attached):
[1] compiler_4.2.0

------- snip -------

Some additional details: The problem occurs both in the R macOS 
console and, if options(help_type="html"), when R is run in a 
terminal window on macOS, but not when options(help_type="text"). 
The former is the default in the Mac R console, the latter when R 
is run in a terminal.

The problem is apparently new in R 4.2.0 -- it doesn't, e.g., occur 
in R 4.1.3. My apologies for not turning it up earlier.

I discovered the problem when accessing help in the Rcmdr GUI, 
which uses tcltk, caused R to hang.

Has anyone else encountered this problem?

Best,
John
-- 
John Fox, Professor Emeritus
McMaster University
Hamilton, Ontario, Canada
web: https://socialsciences.mcmaster.ca/jfox/