[GitHub] [arrow] paleolimbot edited a comment on pull request #12558: ARROW-15841: [R] Implement SafeCallIntoR to safely call the R API from another thread

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paleolimbot edited a comment on pull request #12558:
URL: https://github.com/apache/arrow/pull/12558#issuecomment-1079223791


   Redoing this with an eye towards where I would actually like to use it! I think that it does need a synchronous `Status<cpp_type> SafeCallIntoR<cpp_type>([]() { return r_api_call(); })`, even if all the synchronous version does is error when it's not safe to execute R code. A `SafeCallIntoRAsync()` would also be useful but I'm not sure of the details of how to implement it.
   
   The places where I would prefer to use this in some other PRs:
   
   - https://github.com/apache/arrow/pull/12467/files#diff-b3e736a08e6e6823de704595b9204a1a9907f75c639d32c50cf7b4a79f3e3153R103-R108
   - https://github.com/apache/arrow/pull/12467/files#diff-b3e736a08e6e6823de704595b9204a1a9907f75c639d32c50cf7b4a79f3e3153R144-R146
   - https://github.com/apache/arrow/pull/12323/files#diff-e518a9483c6cdc0c05e79d7ebe59539a3107cd47bb6312d431a83d9d8555a3a9R248-R313
   
   
   
   Some sketch examples:
   
   ``` r
   arrow:::TestSafeCallIntoR(
     function() "string one!",
     opt = "on_main_thread"
   )
   #> [1] "string one!"
   
   arrow:::TestSafeCallIntoR(
     function() stop("This is an error"),
     opt = "on_main_thread"
   )
   #> Error in (function () : This is an error
   
   arrow:::TestSafeCallIntoR(
     function() "string one!",
     opt = "async_with_executor"
   )
   #> [1] "string one!"
   
   # This runs with the expected error, but causes subsequent segfaults, probably related
   # to the error_token_ (maybe having to do with the copy-constructor?)
   
   # arrow:::TestSafeCallIntoR(
   #   function() stop("This is an error"),
   #   opt = "async_with_executor"
   # )
   
   arrow:::TestSafeCallIntoR(
     function() "string one!",
     opt = "async_without_executor"
   )
   #> Error: NotImplemented: Call to R from a non-R thread without an event loop
   ```
   


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