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

[webmail.gandi.net]

Thank you, Ivan for this investigation. I inspected the R changes file (https://cran.r-project.org/doc/manuals/r-devel/NEWS.html) and found nothing about this. I should inspect the sources too!

It could possibly break other Tcl/Tk related stuff. The doc about Tcl_ServiceAll and Tcl_DoOneEvent is confusing. On one hand, it says when Tcl is used from an external program, Tcl_ServiceAll should be used in its event loop instead of Tcl_DoOneEvent (and the change in the latest R versions goes in that direction). But in the other hand, it is indicated that Tcl_ServiceAll does not always handle all Tcl events and extra Tcl_DoOneEvent should be called in this case. I think we spotted one case where Tcl_ServiceAll is not doing its job correctly. There may be others.

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.

Indeed, when I use this on the server side with R 4.3.2:

library(tcltk)
cmd <- r"(
 proc accept {chan addr port} {         ;# Make a proc to accept connections
   puts "$addr:$port says [gets $chan]" ;# Receive a string
   puts $chan goodbye                   ;# Send a string
   close $chan                          ;# Close the socket (automatically flushes)
}                                       ;#
socket -server accept 12345             ;# Create a server socket)"
.Tcl(cmd)
.Tcl("vwait myvar")

It works again as expected. And vwait is known to call Tcl_DoOneEvent. Of course, in this case, R is blocked and waits for the `myvar` variable on the Tcl side. Anyway, the problem seems to be really in Tcl_ServiceAll not catching all Tcl events.

All the best,

Philippe

..............................................<°}))><........
 ) ) ) ) )
( ( ( ( (    Prof. Philippe Grosjean
 ) ) ) ) )
( ( ( ( (    Numerical Ecology
 ) ) ) ) )   Mons University, Belgium
( ( ( ( (
..............................................................

> Le 20 févr. 2024 à 17:13, Ivan Krylov via R-devel <r-devel using r-project.org> a écrit :
> 
> В Tue, 20 Feb 2024 12:27:35 +0100
> "webmail.gandi.net" <phgrosjean using sciviews.org> пишет:
> 
>> When R process #1 is R 4.2.3, it works as expected (whatever version
>> of R #2). When R process #1 is R 4.3.2, nothing is sent or received
>> through the socket apparently, but no error is issued and process #2
>> seems to be able to connect to the socket.
> 
> The difference is related to the change in
> src/library/tcltk/src/tcltk_unix.c.
> 
> In R-4.2.1, the function static void TclSpinLoop(void *data) says:
> 
>    int max_ev = 100;
>    /* Tcl_ServiceAll is not enough here, for reasons that escape me */
>    while (Tcl_DoOneEvent(TCL_DONT_WAIT) && max_ev) max_ev--;
> 
> In R-devel, the function instead says:
> 
>    int i = R_TCL_SPIN_MAX;	
>    while (i-- && Tcl_ServiceAll())
>        ;
> 
> Manually calling Tcl_DoOneEvent(0) from the debugger at this point
> makes the Tcl code respond to the connection. Tcl_ServiceAll() seems to
> be still not enough. I'll try reading Tcl documentation to investigate
> this further.
> 
> -- 
> Best regards,
> Ivan
> 
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> R-devel using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel


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