add debug message when only zeros are copied

weed/filesys/page_writer/chunked_stream_writer.go

@@ -1,6 +1,7 @@
 package page_writer
 
 import (
+	"github.com/chrislusf/seaweedfs/weed/glog"
 	"github.com/chrislusf/seaweedfs/weed/util"
 	"github.com/chrislusf/seaweedfs/weed/util/mem"
 	"io"
@@ -80,6 +81,18 @@ func (cw *ChunkedStreamWriter) ReadDataAt(p []byte, off int64) (maxStop int64) {
 		if logicStart < logicStop {
 			copy(p[logicStart-off:logicStop-off], memChunk.buf[logicStart-memChunkBaseOffset:logicStop-memChunkBaseOffset])
 			maxStop = max(maxStop, logicStop)
+
+			isAllZero := true
+			for i := logicStart - off; i < logicStop-off; i++ {
+				if p[i] != 0 {
+					isAllZero = false
+					break
+				}
+			}
+			if isAllZero {
+				glog.Errorf("Copied content is all Zero [%d,%d)", logicStart-off, logicStop-off)
+			}
+
 		}
 	}
 	return
@@ -111,6 +124,9 @@ func (cw *ChunkedStreamWriter) saveOneChunk(memChunk *MemChunk, logicChunkIndex
 
 // Destroy releases used resources
 func (cw *ChunkedStreamWriter) Destroy() {
+	cw.Lock()
+	defer cw.Unlock()
+
 	for t, memChunk := range cw.activeChunks {
 		mem.Free(memChunk.buf)
 		delete(cw.activeChunks, t)