preallocate StackTrace field Frames

parser/checkpoint.go

@@ -67,8 +67,20 @@ func (c *CheckpointEvent) Parse(r reader.Reader, classes ClassMap, cpools PoolMa
 				results[i] = &threads[i]
 			}
 		case "jdk.types.StackTrace":
+			var pointerToStackFrames []*StackFrame
+			indexPointerToStackFrames := 0
+			getPointerToStackFrames := func(n int) []*StackFrame {
+				if indexPointerToStackFrames+n > len(pointerToStackFrames) {
+					pointerToStackFrames = make([]*StackFrame, m)
+					indexPointerToStackFrames = 0
+				}
+				result := pointerToStackFrames[indexPointerToStackFrames : indexPointerToStackFrames+n]
+				indexPointerToStackFrames += n
+				return result[:0]
+			}
 			stackTraces := make([]StackTrace, m)
 			for i := range stackTraces {
+				stackTraces[i].getPointerToStackFrames = getPointerToStackFrames
 				stackTraces[i].constants = contantsSlice[i]
 				results[i] = &stackTraces[i]
 			}

parser/types.go

@@ -866,10 +866,11 @@ func toStackFrame(p ParseResolvable) (*StackFrame, error) {
 }
 
 type StackTrace struct {
-	Truncated bool
-	Frames    []*StackFrame
-	constants []constant
-	resolved  bool
+	Truncated               bool
+	Frames                  []*StackFrame
+	constants               []constant
+	resolved                bool
+	getPointerToStackFrames func(int) []*StackFrame
 }
 
 func (st *StackTrace) parseField(r reader.Reader, name string, p ParseResolvable) (err error) {
@@ -888,7 +889,7 @@ func (st *StackTrace) parseField(r reader.Reader, name string, p ParseResolvable
 		if err != nil {
 			return err
 		}
-		st.Frames = make([]*StackFrame, 0, frameLen)
+		st.Frames = st.getPointerToStackFrames(int(frameLen))
 	}
 	return err
 }