fix gc for async file writer

async.go

@@ -10,6 +10,9 @@ import (
 
 // AsyncWriter is an Writer that writes asynchronously.
 type AsyncWriter struct {
+	// Writer specifies the writer of output.
+	Writer Writer
+
 	// ChannelSize is the size of the data channel, the default size is 1.
 	ChannelSize uint
 
@@ -19,9 +22,6 @@ type AsyncWriter struct {
 	// WritevDisabled disables the writev syscall if the Writer is a FileWriter.
 	WritevDisabled bool
 
-	// Writer specifies the writer of output.
-	Writer Writer
-
 	once    sync.Once
 	ch      chan *Entry
 	chClose chan error

async_linux.go

@@ -46,6 +46,8 @@ func (w *AsyncWriter) writever() {
 		// return entries to pool
 		for i := 0; i < n; i++ {
 			epool.Put(es[i])
+			es[i] = nil
+			iovs[i].Base = nil
 		}
 	}
 	w.chClose <- err