Gabor,
I think you're talking about two independent things. You can interrupt the
computation, no question about that. It's just that if you send an interrupt
while you're *not* doing any computations, it will be signaled but not raised
until the interrupts are checked since there is no one to check it. This goes
back to my original response - the interactive REPL calls
R_CheckUserInterrupt(), but the straight stdin-prcessing doesn't (since it's
expected to be a script, not interactive prompt). If you just want to clear
interrupts before next processing you can either just run
R_CheckUserInterrupt() explicitly, or on R side do anything that does that,
e.g. to take your example "tryCatch(Sys.sleep(0), interrupt = function(e) e)"
will clear it.
Cheers,
Simon
> On Apr 30, 2019, at 7:03 PM, Gábor Csárdi wrote:
>
> Unfortunately --interactive also makes the session interactive(),
> which is bad for me, as it is a background session.
>
> In general, I don't want the interactive behavior, but was wondering
> if I could send as SIGINT to try to interrupt the computation of the
> background process, and if that does not work, then I would send a
> SIGKILL and start up another process. It all works nicely, except for
> this glitch, but I think I can work around it.
>
> Thanks,
> Gabor
>
> On Tue, Apr 30, 2019 at 10:55 PM Tierney, Luke wrote:
>>
>> A Simon pointed out the interrupt is recorded but not processed until
>> a safe point.
>>
>> When reading from a fifo or pipe R runs non-interactive, which means
>> is sits in a read() system call and the interrupt isn't seen until
>> sometime during evaluation when a safe checkpoint is reached.
>>
>> When reading from a terminal R will use select() to wait for input and
>> periodically wake and check for interrupts. In that case the interrupt
>> will probably be seen sooner.
>>
>> If the interactive behavior is what you want you can add --interactive
>> to the arguments used to start R.
>>
>> Best,
>>
>> luke
>>
>> On Tue, 30 Apr 2019, Gábor Csárdi wrote:
>>
>>> OK, I managed to create an example without callr, but it is still
>>> somewhat cumbersome. Anyway, here it is.
>>>
>>> Terminal 1:
>>> mkfifo fif
>>> R --no-readline --slave --no-save --no-restore < fif
>>>
>>> Terminal 2:
>>> cat > fif
>>> Sys.getpid()
>>>
>>> This will make Terminal 1 print the pid of the R process, so we can
>>> send a SIGINT:
>>>
>>> Terminal 3:
>>> kill -INT pid
>>>
>>> The R process is of course still running happily.
>>>
>>> Terminal 2 again:
>>> tryCatch(Sys.sleep(10), interrupt = function(e) e)
>>>
>>> and then Terminal 1 prints the interrupt condition:
>>>
>>>
>>> This is macOS and 3.5.3, although I don't think it matters much.
>>>
>>> Thanks much!
>>> G.
>>>
>>> On Tue, Apr 30, 2019 at 9:50 PM Simon Urbanek
>>> wrote:
Can you give an example without callr? The key is how is the process
stated and what it is doing which is entirely opaque in callr.
Windows doesn't have signals, so the process there is entirely different.
Most of the WIN32 processing is event-based.
Cheers,
Simon
> On Apr 30, 2019, at 4:17 PM, Gábor Csárdi wrote:
>
> Yeah, I get that they are async.
>
> What happens is that the background process is not doing anything when
> the process gets a SIGINT. I.e. the background process is just
> listening on its standard input.
>
> AFAICT for an interactive process such a SIGINT is just swallowed,
> with a newline outputted to the terminal.
>
> But apparently, for this background process, it is not swallowed, and
> it is triggered later. FWIW it does not happen on Windows, not very
> surprisingly.
>
> Gabor
>
> On Tue, Apr 30, 2019 at 9:13 PM Simon Urbanek
> wrote:
>>
>> Interrupts are not synchronous in R - the signal only flags the request
>> for interruption. Nothing actually happens until R_CheckUserInterrupt()
>> is called at an interruptible point. In you case your code is apparently
>> not calling R_CheckUserInterrupt() until later as a side-effect of the
>> next evaluation.
>>
>> Cheers,
>> Simon
>>
>>
>>> On Apr 30, 2019, at 3:44 PM, Gábor Csárdi
>>> wrote:
>>>
>>> Hi All,
>>>
>>> I realize that this is not a really nice reprex, but anyone has an
>>> idea why a background R session would "remember" an interrupt (SIGINT)
>>> on Unix?
>>>
>>> rs <- callr::r_session$new()
>>> rs$interrupt() # just sends a SIGINT
>>> #> [1] TRUE
>>>
>>> rs$run(function() 1+1)
>>> #> Error: interrupt
>>>
>>> rs$run(function() 1+1)
>>> #> [1] 2
>>>
>>> It seems that the main loop somehow stores the SIGINT it receives
>>> while it is waiting on stdin, and then it triggers it when some input
>>> comes in Maybe. Just speculating
>>>
>>> Thanks,
>>
