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https://issues.apache.org/jira/browse/ARROW-10038?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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ASF GitHub Bot updated ARROW-10038:
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Labels: pull-request-available (was: )
> [C++] SetCpuThreadPoolCapacity(1) spins up nCPUs threads
> --------------------------------------------------------
>
> Key: ARROW-10038
> URL: https://issues.apache.org/jira/browse/ARROW-10038
> Project: Apache Arrow
> Issue Type: Bug
> Components: C++
> Affects Versions: 1.0.1
> Reporter: Adam Hooper
> Assignee: Antoine Pitrou
> Priority: Minor
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> When I call {{arrow::SetCpuThreadPoolCapacity(1);}}, Arrow does this:
> 1. Spins up a singleton {{ThreadPool}} with _the default thread count_;
> 2. Sets the number of threads on that {{ThreadPool}} to 1 -- killing the
> extra threads.
> On my Intel system, I'm forced to spin up four threads to set the CPU
> thread-pool capacity to 1. This goes against the spirit of the API method --
> or at least, my understanding of it (and my experience with other thread
> pools).
> My workaround, for calling code: instead of calling
> {{arrow::SetCpuThreadPoolCapacity(1)}}, call {{setenv("OMP_NUM_THREADS", "1",
> 1)}}.
> Brainstorming, here are some ideas for Arrow's global thread pool that would
> stop launching {{>limit}} threads to set the limit:
> * {{cpu_thread_pool_capacity}} could be a global variable, not an attribute
> on the global {{ThreadPool}}. API users would be expected to set the
> thread-pool capacity _before_ creating the thread pool. (They're probably
> doing this anyway.)
> * {{SetCpuThreadPoolCapacity()}} could call {{setenv("OMP_NUM_THREADS", ...)}}
> * {{ThreadPool}} could create threads on-demand instead of in the ctor. An
> unused {{ThreadPool}} would launch zero threads -- resolving ARROW-10033 as a
> side-effect
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