2 files changed, 35 insertions, 13 deletions

diff --git a/weed/util/limited_async_pool.go b/weed/util/limited_async_pool.go
index c78de158b..51dfd6252 100644
--- a/weed/util/limited_async_pool.go
+++ b/weed/util/limited_async_pool.go
@@ -2,7 +2,11 @@ package util
 
 // initial version comes from https://hackernoon.com/asyncawait-in-golang-an-introductory-guide-ol1e34sg
 
-import "context"
+import (
+	"container/list"
+	"context"
+	"sync"
+)
 
 type Future interface {
 	Await() interface{}
@@ -17,23 +21,27 @@ func (f future) Await() interface{} {
 }
 
 type LimitedAsyncExecutor struct {
-	executor *LimitedConcurrentExecutor
+	executor       *LimitedConcurrentExecutor
+	futureList     *list.List
+	futureListCond *sync.Cond
 }
 
 func NewLimitedAsyncExecutor(limit int) *LimitedAsyncExecutor {
 	return &LimitedAsyncExecutor{
-		executor: NewLimitedConcurrentExecutor(limit),
+		executor:       NewLimitedConcurrentExecutor(limit),
+		futureList:     list.New(),
+		futureListCond: sync.NewCond(&sync.Mutex{}),
 	}
 }
 
-func (ae *LimitedAsyncExecutor) Execute(job func() interface{}) Future {
+func (ae *LimitedAsyncExecutor) Execute(job func() interface{}) {
 	var result interface{}
 	c := make(chan struct{})
 	ae.executor.Execute(func() {
 		defer close(c)
 		result = job()
 	})
-	return future{await: func(ctx context.Context) interface{} {
+	f := future{await: func(ctx context.Context) interface{} {
 		select {
 		case <-ctx.Done():
 			return ctx.Err()
@@ -41,4 +49,18 @@ func (ae *LimitedAsyncExecutor) Execute(job func() interface{}) Future {
 			return result
 		}
 	}}
+	ae.futureListCond.L.Lock()
+	ae.futureList.PushBack(f)
+	ae.futureListCond.Signal()
+	ae.futureListCond.L.Unlock()
+}
+
+func (ae *LimitedAsyncExecutor) NextFuture() Future {
+	ae.futureListCond.L.Lock()
+	for ae.futureList.Len() == 0 {
+		ae.futureListCond.Wait()
+	}
+	f := ae.futureList.Remove(ae.futureList.Front())
+	ae.futureListCond.L.Unlock()
+	return f.(Future)
 }
diff --git a/weed/util/limited_async_pool_test.go b/weed/util/limited_async_pool_test.go
index 935b158da..090ce5375 100644
--- a/weed/util/limited_async_pool_test.go
+++ b/weed/util/limited_async_pool_test.go
@@ -10,17 +10,17 @@ import (
 
 func TestAsyncPool(t *testing.T) {
 	p := NewLimitedAsyncExecutor(3)
-	var results []Future
 
-	results = append(results, p.Execute(FirstFunc))
-	results = append(results, p.Execute(SecondFunc))
-	results = append(results, p.Execute(ThirdFunc))
-	results = append(results, p.Execute(FourthFunc))
-	results = append(results, p.Execute(FifthFunc))
+	p.Execute(FirstFunc)
+	p.Execute(SecondFunc)
+	p.Execute(ThirdFunc)
+	p.Execute(FourthFunc)
+	p.Execute(FifthFunc)
 
 	var sorted_results []int
-	for _, r := range results {
-		x := r.Await().(int)
+	for i := 0; i < 5; i++ {
+		f := p.NextFuture()
+		x := f.Await().(int)
 		println(x)
 		sorted_results = append(sorted_results, x)
 	}