Re: [Rd] Interrupting C++ code execution

From: Simon Urbanek <>
Date: Mon, 25 Apr 2011 09:34:45 -0400

On Apr 25, 2011, at 5:22 AM, wrote:

> Hello,
> I am writing an R interface for one of my C++ programs. The computations in C++ are very time consuming (several hours), so the user needs to be able to interrupt them. Currently, the only way I found to do so is calling R_CheckUserInterrupt() frequently. Unfortunately, there are several problems with that:
> 1. Calling R_CheckUserInterrupt() interrupts immediately, so I have no possibility to exit my code gracefully. In particular, I suppose that objects created on the heap (e.g., STL containers) are not destructed properly.

In general, you're responsible for the cleanup. See R-devel archives for discussion on the interactions of C++ and R error handling. Generally, you should not use local objects and you should use on.exit to make sure you clean up.

> 2. Calling R_CheckUserInterrupt() within a parallel OpenMP loop causes memory corruptions. Even if I do so within a critical section, it usually results in segfaults, crashes, or invalid variable contents afterwards. I suppose this is due to the threads not being destroyed properly. Since most of the time critical computations are done in parallel, this means I can hardly interrupt anything.

As you know R is not thread-safe so you cannot call any R API from a thread - including OMP threads - so obviously you can't call R_CheckUserInterrupt(). Since you're using threads the safe way is to perform your computations on a separate thread and let R handle events so that you can abort your computation thread as part of on.exit.

> Having a function similar to R_CheckUserInterrupt() but returning a boolean variable (has an interrupt occurred or not?) would solve these problems. Is there a way to find out about user interrupt requests (the user pressing ctrl+c or maybe a different set of keys) without interrupting immediately?

Checking for interrupts may involve running the OS event loop (to allow the user to interact with R) and thus is not guaranteed to return. There is no general solution - if you're worried only about your, local code, then on unix, for example, you could use custom signal handlers to set a flag and co-operatively interrupt your program. On Windows there is the UserBreak flag which can be set by a separate thread and thus you may check on it. That said, all this is very much platform-specific.

Simon mailing list Received on Mon 25 Apr 2011 - 13:38:18 GMT

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