[ARROW-11841] [R][C++] Allow cancelling long-running commands

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 10.0.0
• Component/s: C++, R
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/27688
• Assignee: Dewey Dunnington
• Reporter: Antoine Pitrou
• Created: 02/Mar/21 20:03
• Updated: 11/Jan/23 08:22
• Resolved: 03/Oct/22 14:44

Description

When calling a long-running task (for example reading a CSV file) from the R prompt, users may want to interrupt with Ctrl-C.

Allowing this will require integrating R's user interruption facility with the cancellation API that's going to be exposed in C++ (see ARROW-8732).

Below some information I've gathered on the topic:

There is some hairy discussion of how to interrupt C++ code from R at https://stackoverflow.com/questions/40563522/r-how-to-write-interruptible-c-function-and-recover-partial-results and https://stat.ethz.ch/pipermail/r-devel/2011-April/060714.html .

It seems it may involve polling cpp11::check_user_interrupt() and catching any cpp11::unwind_exception that may signal an interruption. A complication is that apparently R APIs should only be called from the main thread. There's also a small library which claims to make writing all this easier: https://github.com/tnagler/RcppThread/blob/master/inst/include/RcppThread/RMonitor.hpp

But since user interruptions will only be noticed by the R main thread, the solution may be to launch heavy computations (e.g. CSV reading) in a separate thread and have the main R thread periodically poll for interrupts while waiting for the separate thread. This is what this dedicated thread class does in its join method: https://github.com/tnagler/RcppThread/blob/master/inst/include/RcppThread/Thread.hpp#L79

Issue Links

• depends upon: ARROW-8732 [C++] Let Futures support cancellation
• is related to: ARROW-17020 [Python][R] GcsFilesystem can appear to hang for non permanent errors
• links to: GitHub Pull Request #13635