1 files changed, 66 insertions, 0 deletions
diff --git a/weed/shell/common.go b/weed/shell/common.go
new file mode 100644
index 000000000..9fe190b31
--- /dev/null
+++ b/weed/shell/common.go
@@ -0,0 +1,66 @@
+package shell
+
+import (
+	"errors"
+	"sync"
+)
+
+// ErrorWaitGroup implements a goroutine wait group which aggregates errors, if any.
+type ErrorWaitGroup struct {
+	maxConcurrency int
+	wg             *sync.WaitGroup
+	wgSem          chan bool
+	errors         []error
+	errorsMu       sync.Mutex
+}
+
+type ErrorWaitGroupTask func() error
+
+func NewErrorWaitGroup(maxConcurrency int) *ErrorWaitGroup {
+	if maxConcurrency <= 0 {
+		// no concurrency = one task at the time
+		maxConcurrency = 1
+	}
+	return &ErrorWaitGroup{
+		maxConcurrency: maxConcurrency,
+		wg:             &sync.WaitGroup{},
+		wgSem:          make(chan bool, maxConcurrency),
+	}
+}
+
+// Reset restarts an ErrorWaitGroup, keeping original settings. Errors and pending goroutines, if any, are flushed.
+func (ewg *ErrorWaitGroup) Reset() {
+	close(ewg.wgSem)
+
+	ewg.wg = &sync.WaitGroup{}
+	ewg.wgSem = make(chan bool, ewg.maxConcurrency)
+	ewg.errors = nil
+}
+
+// Add queues an ErrorWaitGroupTask to be executed as a goroutine.
+func (ewg *ErrorWaitGroup) Add(f ErrorWaitGroupTask) {
+	if ewg.maxConcurrency <= 1 {
+		// keep run order deterministic when parallelization is off
+		ewg.errors = append(ewg.errors, f())
+		return
+	}
+
+	ewg.wg.Add(1)
+	go func() {
+		ewg.wgSem <- true
+
+		err := f()
+		ewg.errorsMu.Lock()
+		ewg.errors = append(ewg.errors, err)
+		ewg.errorsMu.Unlock()
+
+		<-ewg.wgSem
+		ewg.wg.Done()
+	}()
+}
+
+// Wait sleeps until all ErrorWaitGroupTasks are completed, then returns errors for them.
+func (ewg *ErrorWaitGroup) Wait() error {
+	ewg.wg.Wait()
+	return errors.Join(ewg.errors...)
+}