[Rd] cat() in system.time() ?

[Uwe Ligges]

On 17.07.2016 18:13, luke-tierney at uiowa.edu wrote:
> On Fri, 15 Jul 2016, Martin Maechler wrote:
>
>> Hi Ben (and everyone else),
>>
>> as this did not attract attention yet, let me start
>>
>>>>>>> Ben Bolker <bbolker at gmail.com>
>>>>>>>     on Mon, 4 Jul 2016 11:49:40 -0400 writes:
>>
>>    > Does anyone know if there's a reason that proc.time() uses cat()
>>    > rather than message() to print the output when there has been an
>> error
>>    > in the process of timing?
>>
>> This is really not about proc.time(), but  about  system.time()
>> [ and I have corrected the  'Subject' accordingly ] ..
>>
>>    > line 31 of time.R,
>>
>>    >
>> https://github.com/wch/r-source/blob/e5b21d0397c607883ff25cca379687b86933d730/src/library/base/R/time.R#L31
>>
>>
>>    > on.exit(cat("Timing stopped at:", ppt(proc.time() - time), "\n"))
>>
>>    > This means that as far as I can tell the general way to make sure
>>    > there is no output from a timed statement is ...
>>
>>    > tt1 <- capture.output(tt0 <- suppressMessages(suppressWarnings(
>>    >                    try(<stuff to try>, silent=TRUE))))
>>
>>    > (I know I could/should be using tryCatch() instead of try(), but
>> I don't
>>    > think it really matters here ... ?)
>>
>>    > What would people think of a request to change this to message()
>>    > rather than cat() in the future ... ?  (This would mess up code
>> that is
>>    > already using capture.output() to store this information ...)
>>
>> [I think that (last issue) would be acceptable.]
>>
>> One reason of the current cat() may just be historical:
>> message() did not exist yet when  system.time()  was created.
>> However, I agree that that is not good enough a reason to keep
>> it. Much more important is the fact that it is *nice* that the
>> message
>>
>>   Timing stopped at: ...
>>
>> is printed in many cases when a system.time()d call is stopped
>> early.  Quite often for me this is *not* when an error happens
>> as your suppress*() contortions (;-) suggest, but rather when I
>> interrupt the long lasting call.
>> And the current setup nicely gives
>>
>>   > i <- 0; system.time( while(TRUE) i <- i+1 )
>>     C-c C-c
>>   Timing stopped at: 1.001 0.084 1.086
>>   >
>>
>>
>> However, at least this simple case, also works fine with
>> message() instead of cat() ... as I just tried now.
>>
>> A harder case are the "bad errors", e.g.,  memory overflow and
>> similar bad things...
>> cat() seems to be pretty robust, where as message() does invoke
>> a handler (exactly *why* you want it, right?) and that may be
>> harder to keep working correctly after certain errors than a
>> simple cat().
>>
>> I hope that some real experts (on "context switching", "long
>> jumps", etc) would chime in now.
>
> I don't have a strong opinion on whether message would be better or
> not.  But now that the on.exit code is executed after unwinding the C
> call back to the point of the system.time call there is no longer such
> a robustness issue.

I am not sure how much some "R CMD check" extras for reporting 
example/test/vignette runtimes are affected. In case anybody is going to 
change this, please take a careful look or expect to back it out if we 
expewrience problems and have to change code.

Best,
Uwe


>
> Best,
>
> luke
>
>
>>
>> Martin
>>
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>