[jira] [Updated] (ARROW-15841) [R] Implement SafeCallIntoR to safely call the R API from another thread

["ASF GitHub Bot (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/ARROW-15841?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

ASF GitHub Bot updated ARROW-15841:
-----------------------------------
    Labels: pull-request-available  (was: )

> [R] Implement SafeCallIntoR to safely call the R API from another thread
> ------------------------------------------------------------------------
>
>                 Key: ARROW-15841
>                 URL: https://issues.apache.org/jira/browse/ARROW-15841
>             Project: Apache Arrow
>          Issue Type: Improvement
>          Components: R
>            Reporter: Dewey Dunnington
>            Priority: Major
>              Labels: pull-request-available
>          Time Spent: 10m
>  Remaining Estimate: 0h
>
> In ARROW-9235 we have a problem where we need to evaluate code (may be C++ that calls the R API in a way that may allocate R memory or literal R code) on the R main thread. As discussed in the pull request ( https://github.com/apache/arrow/pull/12323#issuecomment-1054726309 ), there are other times that this has come up and will come up in the future (e.g., evaluating user-defined R functions from the query engine, implementing extension types from R).
> After discussing with [~westonpace], it seems like it is worth investing in a {{SafeCallFromR()}} C++ function that lives in the R bindings. The initial approach (that may need to be altered as we go) will be to
> - have a global object that is initialized at the beginning of a C++ call from R to specific functions (and released on exit) that maintains some list of tasks that need to run on the R main thread and an event loop to periodically evaluate them while background tasks are running.
> - define a {{SafeCallFromR()}} C++ function that adds a task to the global object and waits for the result to come back.
> (with apologies to Weston if I mischaracterized our conversation!)



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