Add a benchmark demonstrating lock contention when Marshaling/Unmarshaling maps.
This benchmark is derived from a Google service which experienced poor performance when handling protos with maps.
The current implementation of map decoding uses reflection. In particular reflect.New, reflect.NewAt, and reflect.(*Value).Addr all call reflect.(*rvalue).ptrTo.
reflect.(*rvalue).ptrTo uses a cache protected by a mutex. Grabbing this lock is what causes the problem.
reflect.(*rvalue).ptrTo also implements a fast path (which avoids critical sections) for certain types known to the compiler. Hopefully we can extend the compiler to generate descriptors for more types (https://golang.org/issue/17931) so that we can hit the fast path for all types needed for proto decoding.
PiperOrigin-RevId: 139337589
diff --git a/proto/map_test.go b/proto/map_test.go
new file mode 100644
index 0000000..313e879
--- /dev/null
+++ b/proto/map_test.go
@@ -0,0 +1,46 @@
+package proto_test
+
+import (
+ "fmt"
+ "testing"
+
+ "github.com/golang/protobuf/proto"
+ ppb "github.com/golang/protobuf/proto/proto3_proto"
+)
+
+func marshalled() []byte {
+ m := &ppb.IntMaps{}
+ for i := 0; i < 1000; i++ {
+ m.Maps = append(m.Maps, &ppb.IntMap{
+ Rtt: map[int32]int32{1: 2},
+ })
+ }
+ b, err := proto.Marshal(m)
+ if err != nil {
+ panic(fmt.Sprintf("Can't marshal %+v: %v", m, err))
+ }
+ return b
+}
+
+func BenchmarkConcurrentMapUnmarshal(b *testing.B) {
+ in := marshalled()
+ b.RunParallel(func(pb *testing.PB) {
+ for pb.Next() {
+ var out ppb.IntMaps
+ if err := proto.Unmarshal(in, &out); err != nil {
+ b.Errorf("Can't unmarshal ppb.IntMaps: %v", err)
+ }
+ }
+ })
+}
+
+func BenchmarkSequentialMapUnmarshal(b *testing.B) {
+ in := marshalled()
+ b.ResetTimer()
+ for i := 0; i < b.N; i++ {
+ var out ppb.IntMaps
+ if err := proto.Unmarshal(in, &out); err != nil {
+ b.Errorf("Can't unmarshal ppb.IntMaps: %v", err)
+ }
+ }
+}
diff --git a/proto/proto3_proto/proto3.proto b/proto/proto3_proto/proto3.proto
index 75d5a02..2048655 100644
--- a/proto/proto3_proto/proto3.proto
+++ b/proto/proto3_proto/proto3.proto
@@ -76,3 +76,12 @@
message MessageWithMap {
map<bool, bytes> byte_mapping = 1;
}
+
+
+message IntMap {
+ map<int32, int32> rtt = 1;
+}
+
+message IntMaps {
+ repeated IntMap maps = 1;
+}
