add parallel workers in batch replication (#16609)

internal/workers/workers.go

@@ -0,0 +1,63 @@
+// Copyright (c) 2022-2023 MinIO, Inc.
+//
+// This file is part of MinIO Object Storage stack
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package workers
+
+import (
+	"errors"
+	"sync"
+)
+
+// Workers provides a bounded semaphore with the ability to wait until all
+// concurrent jobs finish.
+type Workers struct {
+	wg    sync.WaitGroup
+	queue chan struct{}
+}
+
+// New creates a Workers object which allows up to n jobs to proceed
+// concurrently. n must be > 0.
+func New(n int) (*Workers, error) {
+	if n <= 0 {
+		return nil, errors.New("n must be > 0")
+	}
+
+	queue := make(chan struct{}, n)
+	for i := 0; i < n; i++ {
+		queue <- struct{}{}
+	}
+	return &Workers{
+		queue: queue,
+	}, nil
+}
+
+// Take is how a job (goroutine) can Take its turn.
+func (jt *Workers) Take() {
+	jt.wg.Add(1)
+	<-jt.queue
+}
+
+// Give is how a job (goroutine) can give back its turn once done.
+func (jt *Workers) Give() {
+	jt.queue <- struct{}{}
+	jt.wg.Done()
+}
+
+// Wait waits for all ongoing concurrent jobs to complete
+func (jt *Workers) Wait() {
+	jt.wg.Wait()
+}