[Rd] Tcl socket server (tcltk) does not work any more on R 4.3.2

[Ivan Krylov]

В Wed, 21 Feb 2024 08:01:16 +0100
"webmail.gandi.net" <phgrosjean using sciviews.org> пишет:

> Since the {tcltk} package was working fine with  "while
> (Tcl_DoOneEvent(TCL_DONT_WAIT) && max_ev) max_ev—;", unless there is
> a clear performance enhancement with "while (i-- &&
> Tcl_ServiceAll())", it would perhaps be wise to revert this back.

I forgot to mention the comment in the new version of the function
explaining the switch:

>> [Tcl_DoOneEvent(TCL_DONT_WAIT)] <...> causes infinite recursion with
>> R handlers that have a re-entrancy guard, when TclSpinLoop is
>> invoked from such a handler (seen with Rhttp server)

The difference between Tcl_ServiceAll() and Tcl_DoOneEvent() is that
the latter calls Tcl_WaitForEvent(). The comments say that it is called
for the side effect of queuing the events detected by select(). The
function can indeed be observed to access the fileHandlers via the
thread-specific data pointer, which contain the file descriptors and
the instructions saying what to do with them.

Without Tcl_WaitForEvent, the only event sources known to Tcl are
RTcl_{setup,check}Proc (which only checks file descriptors owned by R),
Display{Setup,Check}Proc (which seems to be owned by Tk), and
Timer{Setup,Check}Proc (for which there doesn't seem to be any timers
by default).

As far as I understand the problem, while the function
worker_input_handler() from src/modules/internet/Rhttpd.c is running,
TclHandler() might be invoked, causing Tcl_DoOneEvent() to call
RTcl_checkProc() and therefore trying to run worker_input_handler()
again. The Rhttpd handler prevents this and doesn't clear the
condition, which causes the event loop to keep calling it. Is that
correct? Are there easy ways to reproduce the problem?

-- 
Best regards,
Ivan