Enhancement

README.md

@@ -30,10 +30,21 @@ The parser API is pretty straightforward:
 func Parse(r io.Reader) ([]Chunk, error)
 ```
 
-Parser returns a slice of chunks, each containing a slice of events. It should be used like this:
+Parser returns a slice of chunks, for each chunk call chunk.Next and then read chunk.Event. 
+
+It should be used like this:
 
 ```go
 chunks, err := parser.Parse(reader)
+for _, chunk := range chunks {
+    for chunk.Next() {
+        chunk.Event // it may be reused, copy it if you need the event after another call to Next
+    }
+    err = chunk.Err()
+    if err != nil {
+        panic(err)
+    }
+}
 ```
 
 Check the [main](./main.go) package for further details. It can also be used to validate the parser works with your data and get some basic stats.

parser/checkpoint.go

@@ -39,27 +39,140 @@ func (c *CheckpointEvent) Parse(r reader.Reader, classes ClassMap, cpools PoolMa
 		if err != nil {
 			return fmt.Errorf("unable to parse constant pool class: %w", err)
 		}
+		m, err := r.VarInt()
+		if err != nil {
+			return fmt.Errorf("unable to parse constant pool's number of constants: %w", err)
+		}
 		cm, ok := cpools[int(classID)]
 		if !ok {
-			cpools[int(classID)] = &CPool{Pool: make(map[int]ParseResolvable)}
+			cpools[int(classID)] = &CPool{Pool: make(map[int]ParseResolvable, m)}
 			cm = cpools[int(classID)]
 		}
-		m, err := r.VarInt()
-		if err != nil {
-			return fmt.Errorf("unable to parse constant pool's number of constants: %w", err)
+		class, ok := classes[int(classID)]
+		if !ok {
+			return fmt.Errorf("unexpected class %d", classID)
+		}
+		var (
+			results            []ParseResolvable
+			preAllocateResults = true
+			contantsSlice      = getConstantsSlice(int(m), class.numConstants)
+		)
+		// preallocate common class in async-profiler
+		results = make([]ParseResolvable, m)
+		switch class.Name {
+		case "java.lang.Thread":
+			threads := make([]Thread, m)
+			for i := range threads {
+				threads[i].constants = contantsSlice[i]
+				results[i] = &threads[i]
+			}
+		case "jdk.types.StackTrace":
+			var classStackFrames *ClassMetadata
+			for _, class := range classes {
+				if class.Name == "jdk.types.StackFrame" {
+					classStackFrames = class
+					break
+				}
+			}
+			var (
+				stackFrames      []StackFrame
+				indexStackFrames int
+			)
+			createStackFrames := func() ParseResolvable {
+				if indexStackFrames >= len(stackFrames) {
+					stackFrames = make([]StackFrame, m)
+					contantsSlice = getConstantsSlice(int(m), classStackFrames.numConstants)
+					for i := range stackFrames {
+						stackFrames[i].constants = contantsSlice[i]
+					}
+					indexStackFrames = 0
+				}
+				result := &stackFrames[indexStackFrames]
+				indexStackFrames++
+				return result
+			}
+			for i, class := range classes {
+				if class.Name == "jdk.types.StackFrame" {
+					class.typeFn = createStackFrames
+					classes[i] = class
+					break
+				}
+			}
+			var pointerToStackFrames []*StackFrame
+			indexPointerToStackFrames := 0
+			getPointerToStackFrames := func(n int) []*StackFrame {
+				if n > int(m) {
+					return make([]*StackFrame, n)[:0]
+				}
+				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]
+			}
+		case "jdk.types.Method":
+			methods := make([]Method, m)
+			for i := range methods {
+				methods[i].constants = contantsSlice[i]
+				results[i] = &methods[i]
+			}
+		case "java.lang.Class":
+			classes := make([]Class, m)
+			for i := range classes {
+				classes[i].constants = contantsSlice[i]
+				results[i] = &classes[i]
+			}
+		case "jdk.types.Package":
+			packages := make([]Package, m)
+			for i := range packages {
+				packages[i].constants = contantsSlice[i]
+				results[i] = &packages[i]
+			}
+		case "jdk.types.Symbol":
+			symbols := make([]Symbol, m)
+			for i := range symbols {
+				symbols[i].constants = contantsSlice[i]
+				results[i] = &symbols[i]
+			}
+		default:
+			preAllocateResults = false
 		}
 		// TODO: assert m is small enough
 		for j := 0; j < int(m); j++ {
 			idx, err := r.VarLong()
 			if err != nil {
 				return fmt.Errorf("unable to parse contant's index: %w", err)
 			}
-			v, err := ParseClass(r, classes, cpools, classID)
-			if err != nil {
-				return fmt.Errorf("unable to parse constant type %d: %w", classID, err)
+
+			var v ParseResolvable
+			if preAllocateResults {
+				v = results[j]
+				err = v.Parse(r, classes, cpools, class)
+			} else {
+				v, err = ParseClass(r, classes, cpools, classID)
+				if err != nil {
+					return fmt.Errorf("unable to parse constant type %d: %w", classID, err)
+				}
 			}
 			cm.Pool[int(idx)] = v
 		}
 	}
 	return nil
 }
+
+func getConstantsSlice(size int, num int) [][]constant {
+	constants := make([]constant, size*num)
+	contantsSlice := make([][]constant, size)
+	for i := range contantsSlice {
+		contantsSlice[i] = constants[i*num : (i+1)*num][:0]
+	}
+	return contantsSlice
+}