Antoine Pitrou created ARROW-11841:
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Summary: [R][C++] Allow cancelling long-running commands
Key: ARROW-11841
URL: https://issues.apache.org/jira/browse/ARROW-11841
Project: Apache Arrow
Issue Type: Improvement
Components: C++, R
Reporter: Antoine Pitrou
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
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