[PR] Make default `NumParallel` cgroup-aware. [arrow-go]

["samueleresca (via GitHub)" <gi...@apache.org>]

samueleresca opened a new pull request, #1384:
URL: https://github.com/apache/arrow-go/pull/1384

   ### Rationale for this change
   
   Since Go 1.25+, `runtime.GOMAXPROCS(0)` is cgroup-aware. See [Release notes](https://go.dev/doc/go1.25#runtime).
   `runtime.NumCPU()` reflects the number of CPUs on the host without taking into account cgroup limits. 
   
   The issue has an impact in any containerised environment (e.g., k8s) when setting limits.
   
   ### What changes are included in this PR?
   
   Switching from `NumParallel = runtime.NumCPU()` to `NumParallel = runtime.GOMAXPROCS(0)`
   
   ### Are these changes tested?
   
   Tested manually using:
   ```go
   package compute_test
   
   import (
   	"runtime"
   	"testing"
   
   	"github.com/apache/arrow-go/v18/arrow/compute"
   )
   
   func TestCgroupDemo(t *testing.T) {
   	t.Logf("NumCPU=%d GOMAXPROCS=%d DefaultExecCtx.NumParallel=%d",
   		runtime.NumCPU(), runtime.GOMAXPROCS(0), compute.DefaultExecCtx().NumParallel)
   }
   ```
   
   and running with and without the change:
   ```bash
   go test -c -o /tmp/c.test ./arrow/compute                                       
   systemd-run --user --scope -q -p CPUQuota=200% /tmp/c.test -test.run CgroupDemo -test.v
   ```
   
   
   ### Are there any user-facing changes?
   
   Yes, a small behavioural change to the default:
   - When GOMAXPROCS is lower than the CPU count, whether set by the environment variable, set by a cgroup limit on Go 1.25 or later, or set in code before package init, the default `NumParallel` is now lower than before. 
   - The default is read once at package init. A later call to runtime.GOMAXPROCS(n) won't change it.
   - Callers can still override it with `SetExecCtx` or `ExecCtx.NumParallel`.
   - There are no API or signature changes.
   
   


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Re: [PR] fix(arrow/compute): respect GOMAXPROCS for default NumParallel [arrow-go]

["zeroshade (via GitHub)" <gi...@apache.org>]

zeroshade merged PR #1384:
URL: https://github.com/apache/arrow-go/pull/1384


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