v8.Value becomes manually releaseable (rogchap#361)

* values are manually releaseable

Co-authored-by: Kyle Maxwell <kyle.maxwell@reddit.com>

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+- Added support for Value.release() and FunctionCallbackInfo.release(). This is useful when using v8go in a long-running context.
+
 ### Fixed
 - Use string length to ensure null character-containing strings in Go/JS are not terminated early.
 - Object.Set with an empty key string is now supported

context.go

@@ -81,6 +81,12 @@ func (c *Context) Isolate() *Isolate {
 	return c.iso
 }
 
+func (c *Context) RetainedValueCount() int {
+	ctxMutex.Lock()
+	defer ctxMutex.Unlock()
+	return int(C.ContextRetainedValueCount(c.ptr))
+}
+
 // RunScript executes the source JavaScript; origin (a.k.a. filename) provides a
 // reference for the script and used in the stack trace if there is an error.
 // error will be of type `JSError` if not nil.

context_test.go

@@ -104,8 +104,8 @@ func TestMemoryLeak(t *testing.T) {
 
 	for i := 0; i < 6000; i++ {
 		ctx := v8.NewContext(iso)
-		obj := ctx.Global()
-		_ = obj.String()
+		_ = ctx.Global()
+		// _ = obj.String()
 		_, _ = ctx.RunScript("2", "")
 		ctx.Close()
 	}

function_template.go

@@ -37,6 +37,13 @@ func (i *FunctionCallbackInfo) Args() []*Value {
 	return i.args
 }
 
+func (i *FunctionCallbackInfo) Release() {
+	for _, arg := range i.args {
+		arg.Release()
+	}
+	i.this.Release()
+}
+
 // FunctionTemplate is used to create functions at runtime.
 // There can only be one function created from a FunctionTemplate in a context.
 // The lifetime of the created function is equal to the lifetime of the context.

function_template_test.go

@@ -48,6 +48,45 @@ func TestFunctionTemplate_panic_on_nil_callback(t *testing.T) {
 	defer iso.Dispose()
 	v8.NewFunctionTemplate(iso, nil)
 }
+func TestFunctionTemplate_generates_values(t *testing.T) {
+	t.Parallel()
+
+	iso := v8.NewIsolate()
+	defer iso.Dispose()
+	global := v8.NewObjectTemplate(iso)
+	printfn := v8.NewFunctionTemplate(iso, func(info *v8.FunctionCallbackInfo) *v8.Value {
+		fmt.Printf("%+v\n", info.Args())
+		return nil
+	})
+	global.Set("print", printfn, v8.ReadOnly)
+	ctx := v8.NewContext(iso, global)
+	defer ctx.Close()
+	ctx.RunScript("print('foo', 'bar', 0, 1)", "")
+	if ctx.RetainedValueCount() != 6 {
+		t.Errorf("expected 6 retained values, got: %d", ctx.RetainedValueCount())
+	}
+}
+
+func TestFunctionTemplate_releases_values(t *testing.T) {
+	t.Parallel()
+
+	iso := v8.NewIsolate()
+	defer iso.Dispose()
+	global := v8.NewObjectTemplate(iso)
+	printfn := v8.NewFunctionTemplate(iso, func(info *v8.FunctionCallbackInfo) *v8.Value {
+		defer info.Release()
+		fmt.Printf("%+v\n", info.Args())
+		return nil
+	})
+	global.Set("print", printfn, v8.ReadOnly)
+	ctx := v8.NewContext(iso, global)
+	defer ctx.Close()
+	ctx.RunScript("print('foo', 'bar', 0, 1)", "")
+	// there is a constant factor associated with the global.
+	if ctx.RetainedValueCount() != 1 {
+		t.Errorf("expected 1 retained values, got: %d", ctx.RetainedValueCount())
+	}
+}
 
 func TestFunctionTemplateGetFunction(t *testing.T) {
 	t.Parallel()