[Rd] BUG?: On Linux setTimeLimit() fails to propagate timeout error when it occurs (works on Windows)

[Henrik Bengtsson]

Thank you for the feedback and confirmations.  Interesting to see that
it's also reproducible on macOS expect for Spencer; that might
indicate a difference in builds.

BTW, my original post suggested that timeout error was for sure
detected while running Sys.sleep(10).  However, it could of course
also be that it is only detected after it finishes.


For troubleshooting, the help("setTimeLimit", package = "base") says that:

* "Time limits are checked whenever a user interrupt could occur. This
will happen frequently in R code and during Sys.sleep, but only at
points in compiled C and Fortran code identified by the code author."

The example here uses Sys.sleep(), which supports and detects user interrupts.


The timeout error message is thrown by the R_ProcessEvents(void)
function as defined in:

* src/unix/sys-unix.c
(https://github.com/wch/r-source/blob/trunk/src/unix/sys-unix.c#L421-L453)
* src/gnuwin32/system.c
(https://github.com/wch/r-source/blob/trunk/src/gnuwin32/system.c#L110-L140)

So, they're clearly different implementations on Windows and Unix.
Also, for the Unix implementation, the code differ based on
preprocessing directive HAVE_AQUA, which could explain why Spencer
observes a different behavior than Peter and Berend (all on macOS).


Whenever the R_CheckUserInterrupt() function is called it in turn
always calls R_ProcessEvents().  At the end, there is a code snippet -
if (R_interrupts_pending) onintr(); - which is Windows specific and
could be another important difference between Windows and Unix.  This
function is defined in:

* src/main/errors.c
(https://github.com/wch/r-source/blob/trunk/src/main/errors.c#L114-L134)


The do_setTimeLimit() function controls global variables cpuLimitValue
and elapsedLimitValue, which are checked in R_ProcessEvents(), but
other than setting the timeout limits I don't think it's involved in
the runtime checks. The do_setTimeLimit() is defined in:

* src/main/sysutils.c
(https://github.com/wch/r-source/blob/trunk/src/main/sysutils.c#L1692-L1736)


Unfortunately, right now, I've got little extra time to troubleshoot
this further.

/Henrik

On Wed, Oct 26, 2016 at 2:22 AM, Berend Hasselman <bhh at xs4all.nl> wrote:
>
>> On 26 Oct 2016, at 04:44, Henrik Bengtsson <henrik.bengtsson at gmail.com> wrote:
>> .......
>> This looks like a bug to me.  Can anyone on macOS confirm whether this
>> is also a problem there or not?
>>
>
>
> Tried it on macOS El Capitan and got this (running in R.app with R version 3.3.2 RC (2016-10-23 r71574):
>
>> setTimeLimit(elapsed=1)
>> system.time({ Sys.sleep(10); message("done") })
> Error in Sys.sleep(10) : reached elapsed time limit
> Timing stopped at: 0.113 0.042 10.038
>
> Berend
>