Implement NewValueExternal and ValueToExternal for sharing Golang structs; add external value management in ExternalStore

Author: trheyi

external.go

@@ -0,0 +1,101 @@
+package v8go
+
+// #include <stdlib.h>
+// #include "v8go.h"
+import "C"
+import (
+	"errors"
+	"sync"
+	"unsafe"
+)
+
+// ExternalStore is a store for external values.
+type ExternalStore struct {
+	counter uintptr
+	store   sync.Map
+	lock    sync.Mutex
+}
+
+var externals = NewExternalStore()
+
+// NewExternalStore creates a new ExternalStore.
+func NewExternalStore() *ExternalStore {
+	return &ExternalStore{
+		counter: 0,
+		store:   sync.Map{},
+		lock:    sync.Mutex{},
+	}
+}
+
+// Get returns a value from the store.
+func (s *ExternalStore) Get(key uintptr) (interface{}, bool) {
+	return s.store.Load(key)
+}
+
+// Add adds a value to the store. It returns a key that can be used to retrieve the value.
+func (s *ExternalStore) Add(value interface{}) uintptr {
+	s.lock.Lock()
+	defer s.lock.Unlock()
+	s.counter++
+	s.store.Store(s.counter, value)
+	return s.counter
+}
+
+// Remove removes a value from the store.
+func (s *ExternalStore) Remove(key uintptr) {
+	s.store.Delete(key)
+}
+
+// ExternalCount returns the number of external values in the store.
+func ExternalCount() int {
+	count := 0
+	externals.store.Range(func(_, _ interface{}) bool {
+		count++
+		return true
+	})
+	return count
+}
+
+// NewExternal creates a new external value.
+func NewExternal(iso *Isolate, val interface{}) (*Value, error) {
+	ptr := externals.Add(val)
+	rtnVal := &Value{
+		ptr: C.NewValueExternal(iso.ptr, unsafe.Pointer(ptr)),
+	}
+	return rtnVal, nil
+}
+
+// External returns the external value.
+// then an error is returned. Use `value.Object()` to do the JS equivalent of `Object(value)`.
+func (v *Value) External() (interface{}, error) {
+	if !v.IsYaoExternal() {
+		return nil, errors.New("v8go: value is not an External")
+	}
+
+	rtnValue := C.ValueToExternal(v.ptr)
+	if rtnValue == 0 {
+		return nil, errors.New("v8go: failed to get external value")
+	}
+
+	value, ok := externals.Get(uintptr(rtnValue))
+	if !ok {
+		return nil, errors.New("v8go: failed to get external value, not found")
+	}
+
+	return value, nil
+}
+
+// IsYaoExternal returns true if the value is an external value.
+func (v *Value) IsYaoExternal() bool {
+	return C.ValueIsExternal(v.ptr) != 0
+}
+
+// ReleaseExternal releases the external value.
+func (v *Value) ReleaseExternal() {
+	if v.IsYaoExternal() {
+		rtnValue := C.ValueToExternal(v.ptr)
+		if rtnValue != 0 {
+			externals.Remove(uintptr(rtnValue))
+		}
+	}
+}

external_test.go

@@ -0,0 +1,45 @@
+package v8go_test
+
+import (
+	"testing"
+
+	v8 "rogchap.com/v8go"
+)
+
+func TestExternal(t *testing.T) {
+	t.Parallel()
+
+	ctx := v8.NewContext()
+	defer ctx.Isolate().Dispose()
+	defer ctx.Close()
+
+	goValue := map[string]interface{}{"foo": "bar"}
+	val, err := v8.NewExternal(ctx.Isolate(), goValue)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if !val.IsYaoExternal() {
+		t.Errorf("expected value to be of type External")
+	}
+
+	resValue, err := val.External()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	v, ok := resValue.(map[string]interface{})
+	if !ok {
+		t.Errorf("expected value to be of type map[string]interface{}")
+	}
+
+	if v["foo"] != "bar" {
+		t.Errorf("expected value to be 'bar', got %v", v["foo"])
+	}
+
+	// Release the external value
+	val.Release()
+	if v8.ExternalCount() != 0 {
+		t.Errorf("expected external count to be 0, got %v", v8.ExternalCount())
+	}
+}

v8go.cc

@@ -989,6 +989,18 @@ ValuePtr NewValueBigIntFromUnsigned(IsolatePtr iso, uint64_t v) {
   return tracked_value(ctx, val);
 }
 
+ValuePtr NewValueExternal(IsolatePtr iso, void* v) {
+  ISOLATE_SCOPE_INTERNAL_CONTEXT(iso);
+  m_value* val = new m_value;
+  val->id = 0;
+  val->iso = iso;
+  val->ctx = ctx;
+  val->ptr = Persistent<Value, CopyablePersistentTraits<Value>>(
+      iso, External::New(iso, v));
+  return tracked_value(ctx, val);
+}
+
+
 RtnValue NewValueBigIntFromWords(IsolatePtr iso,
                                  int sign_bit,
                                  int word_count,
@@ -1040,6 +1052,15 @@ int64_t ValueToInteger(ValuePtr ptr) {
   return value->IntegerValue(local_ctx).ToChecked();
 }
 
+uint64_t ValueToExternal(ValuePtr ptr) {
+  LOCAL_VALUE(ptr);
+  if (value->IsExternal()) {
+    Local<External> external = value.As<External>();
+    return reinterpret_cast<uint64_t>(external->Value());
+  }
+  return 0;
+}
+
 double ValueToNumber(ValuePtr ptr) {
   LOCAL_VALUE(ptr);
   return value->NumberValue(local_ctx).ToChecked();

v8go.h

@@ -224,6 +224,8 @@ extern RtnValue NewValueBigIntFromWords(IsolatePtr iso_ptr,
                                         int sign_bit,
                                         int word_count,
                                         const uint64_t* words);
+extern ValuePtr NewValueExternal(IsolatePtr iso_ptr, void* v); // Yao App Engine: Implement NewValueExternal to Share Golang Structs
+
 void ValueRelease(ValuePtr ptr);
 extern RtnString ValueToString(ValuePtr ptr);
 const uint32_t* ValueToArrayIndex(ValuePtr ptr);
@@ -233,6 +235,7 @@ int64_t ValueToInteger(ValuePtr ptr);
 double ValueToNumber(ValuePtr ptr);
 RtnString ValueToDetailString(ValuePtr ptr);
 uint32_t ValueToUint32(ValuePtr ptr);
+uint64_t ValueToExternal(ValuePtr ptr); // Yao App Engine: Implement ValueToExternal to Share Golang Structs
 extern ValueBigInt ValueToBigInt(ValuePtr ptr);
 extern RtnValue ValueToObject(ValuePtr ptr);
 int ValueSameValue(ValuePtr ptr, ValuePtr otherPtr);

value.go

@@ -534,6 +534,11 @@ func (v *Value) IsProxy() bool {
 
 // Release this value.  Using the value after calling this function will result in undefined behavior.
 func (v *Value) Release() {
+
+	// Yao: Before releasing the value, we need to release the external object
+	// if it is an external object.
+	v.ReleaseExternal()
+
 	C.ValueRelease(v.ptr)
 }