Config: Parallel for for inbounds' clients (#6055)

https://github.com/XTLS/Xray-core/pull/6055#issuecomment-4360958652

common/task/parallel.go

@@ -0,0 +1,43 @@
+package task
+
+import (
+	"runtime"
+
+	"golang.org/x/sync/errgroup"
+)
+
+// ParallelForN runs fn(0..n-1) in parallel across runtime.GOMAXPROCS(0) worker
+// goroutines. Indices are partitioned into contiguous chunks so the number of
+// spawned goroutines stays bounded regardless of n.
+//
+// fn must be safe to call concurrently from different goroutines (each call
+// receives its own unique index). Output collected by writing to indexed slots
+// in a pre-allocated slice is a common safe pattern.
+//
+// Returns the first non-nil error reported by fn; other workers may still be
+// finishing briefly afterwards.
+func ParallelForN(n int, fn func(i int) error) error {
+	if n <= 0 {
+		return nil
+	}
+	workers := max(runtime.GOMAXPROCS(0), 1)
+	workers = min(workers, n)
+	chunk := (n + workers - 1) / workers
+	var eg errgroup.Group
+	for w := range workers {
+		start := w * chunk
+		end := min(start+chunk, n)
+		if start >= end {
+			break
+		}
+		eg.Go(func() error {
+			for i := start; i < end; i++ {
+				if err := fn(i); err != nil {
+					return err
+				}
+			}
+			return nil
+		})
+	}
+	return eg.Wait()
+}