Added mutex to Checkpoint function to avoid racey conditions

kcl/kcl.go

@@ -6,6 +6,7 @@ import (
 	"encoding/json"
 	"fmt"
 	"io"
+	"sync"
 )
 
 type RecordProcessor interface {
@@ -23,6 +24,8 @@ func (ce CheckpointError) Error() string {
 }
 
 type Checkpointer struct {
+	mux sync.Mutex
+
 	ioHandler ioHandler
 }
 
@@ -39,6 +42,9 @@ func (c *Checkpointer) getAction() (interface{}, error) {
 }
 
 func (c *Checkpointer) Checkpoint(sequenceNumber *string, subSequenceNumber *int) error {
+	c.mux.Lock()
+	defer c.mux.Unlock()
+
 	c.ioHandler.writeAction(ActionCheckpoint{
 		Action:            "checkpoint",
 		SequenceNumber:    sequenceNumber,
@@ -62,7 +68,6 @@ func (c *Checkpointer) Checkpoint(sequenceNumber *string, subSequenceNumber *int
 		}
 	}
 	return nil
-
 }
 
 type ioHandler struct {