we need a safe encoder, not just a safe writer

2 files changed, 20 insertions, 1 deletions

diff --git a/skate/reduce.go b/skate/reduce.go
index 8325bc0..61e8cd6 100644
--- a/skate/reduce.go
+++ b/skate/reduce.go
@@ -64,7 +64,7 @@ func groupLogf(g *zipkey.Group, s string, vs ...interface{}) {
 // match result, e.g. for doi matches.
 func ZippyExact(releases, refs io.Reader, matchResult MatchResult, w io.Writer) error {
 	var (
-		enc     = json.NewEncoder(xio.NewSingleWriter(w))
+		enc     = xio.NewSafeEncoder(json.NewEncoder(w))
 		keyer   = makeKeyFunc("\t", 1)
 		i       = 0
 		bref    BiblioRef
diff --git a/skate/xio/util.go b/skate/xio/util.go
index 49f38a3..9f6cc26 100644
--- a/skate/xio/util.go
+++ b/skate/xio/util.go
@@ -9,6 +9,25 @@ import (
 	"sync"
 )
 
+type Encoder interface {
+	Encode(interface{}) error
+}
+
+type SafeEncoder struct {
+	sync.Mutex
+	enc Encoder
+}
+
+func NewSafeEncoder(enc Encoder) *SafeEncoder {
+	return &SafeEncoder{enc: enc}
+}
+
+func (s *SafeEncoder) Encode(v interface{}) error {
+	s.Lock()
+	defer s.Unlock()
+	return s.enc.Encode(v)
+}
+
 // SingleWriter makes any writer thread safe.
 type SingleWriter struct {
 	sync.Mutex