revert to same implementation as before

This reverts commit 7e8edc3c4a.

weed/filesys/wfs.go

@@ -77,7 +77,7 @@ type WFS struct {
 	signature  int32
 
 	// throttle writers
-	concurrentWriters *util.LimitedOutOfOrderProcessor
+	concurrentWriters *util.LimitedConcurrentExecutor
 	Server            *fs.Server
 }
 type statsCache struct {
@@ -135,7 +135,7 @@ func NewSeaweedFileSystem(option *Option) *WFS {
 	wfs.fsNodeCache = newFsCache(wfs.root)
 
 	if wfs.option.ConcurrentWriters > 0 {
-		wfs.concurrentWriters = util.NewLimitedOutOfOrderProcessor(int32(wfs.option.ConcurrentWriters))
+		wfs.concurrentWriters = util.NewLimitedConcurrentExecutor(wfs.option.ConcurrentWriters)
 	}
 
 	return wfs

weed/util/limiter.go

@@ -7,6 +7,46 @@ import (
 	"sync/atomic"
 )
 
+// initial version comes from https://github.com/korovkin/limiter/blob/master/limiter.go
+
+// LimitedConcurrentExecutor object
+type LimitedConcurrentExecutor struct {
+	limit     int
+	tokenChan chan int
+}
+
+func NewLimitedConcurrentExecutor(limit int) *LimitedConcurrentExecutor {
+
+	// allocate a limiter instance
+	c := &LimitedConcurrentExecutor{
+		limit:     limit,
+		tokenChan: make(chan int, limit),
+	}
+
+	// allocate the tokenChan:
+	for i := 0; i < c.limit; i++ {
+		c.tokenChan <- i
+	}
+
+	return c
+}
+
+// Execute adds a function to the execution queue.
+// if num of go routines allocated by this instance is < limit
+// launch a new go routine to execute job
+// else wait until a go routine becomes available
+func (c *LimitedConcurrentExecutor) Execute(job func()) {
+	token := <-c.tokenChan
+	go func() {
+		defer func() {
+			c.tokenChan <- token
+		}()
+		// run the job
+		job()
+	}()
+}
+
+// a different implementation, but somehow more "conservative"
 type OperationRequest func()
 
 type LimitedOutOfOrderProcessor struct {