R: How to write interruptible C++ function, and recover partial results

Question

We are writing an R package, the core of which is written in C++ and basically consists of one long-running loop:

void core_func(double* data)
{
    while (!         


        

Answer 1

Update: the easiest approach is to call C++ via Rcpp and check via Rcpp::checkUserInterrupt. This automatically raises an exception if a interrupt is pending. See section 2.4 of rcpp attributes.

Original answer: R allows for checking for SIGINT via the C API:

R_CheckUserInterrupt();

However this function will immediately jump back to the console if an interruption is pending which can leave your C/C++ code in an undefined state.

A trick suggested by Simon Urbanek is to use the following wrapper code:

/* Check for interrupt without long jumping */
void check_interrupt_fn(void *dummy) {
  R_CheckUserInterrupt();
}

int pending_interrupt() {
  return !(R_ToplevelExec(check_interrupt_fn, NULL));
}

You can now call pending_interrupt() to check if an interruption is pending and deal with it yourself, e.g. raise some special C++ exception or simply return intermediate results. Make sure you read Simon's comments in the post to understand the consequences of this approach.

I have personally only used this via C to interrupt downloads in the curl package. Perhaps you can search metacran for examples that use R_CheckUserInterrupt from C++.