avoid possible deadlock: move metadata log flush channel out of lock scope

weed/util/log_buffer/log_buffer.go

@@ -58,9 +58,13 @@ func NewLogBuffer(name string, flushInterval time.Duration, flushFn func(startTi
 
 func (m *LogBuffer) AddToBuffer(partitionKey, data []byte, processingTsNs int64) {
 
+	var toFlush *dataToFlush
 	m.Lock()
 	defer func() {
 		m.Unlock()
+		if toFlush != nil {
+			m.flushChan <- toFlush
+		}
 		if m.notifyFn != nil {
 			m.notifyFn()
 		}
@@ -96,7 +100,7 @@ func (m *LogBuffer) AddToBuffer(partitionKey, data []byte, processingTsNs int64)
 
 	if m.startTime.Add(m.flushInterval).Before(ts) || len(m.buf)-m.pos < size+4 {
 		// glog.V(4).Infof("%s copyToFlush1 start time %v, ts %v, remaining %d bytes", m.name, m.startTime, ts, len(m.buf)-m.pos)
-		m.flushChan <- m.copyToFlush()
+		toFlush = m.copyToFlush()
 		m.startTime = ts
 		if len(m.buf) < size+4 {
 			m.buf = make([]byte, 2*size+4)
@@ -148,8 +152,10 @@ func (m *LogBuffer) loopInterval() {
 			return
 		}
 		toFlush := m.copyToFlush()
-		m.flushChan <- toFlush
 		m.Unlock()
+		if toFlush != nil {
+			m.flushChan <- toFlush
+		}
 	}
 }