[wasm] Add a Managed<T> wrapper class for allocating C++ classes that are deleted when the wrapper …

src/wasm/managed.h

+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_WASM_MANAGED_H_
+#define V8_WASM_MANAGED_H_
+
+#include "src/factory.h"
+#include "src/global-handles.h"
+#include "src/handles.h"
+#include "src/isolate.h"
+#include "src/objects-inl.h"
+
+namespace v8 {
+namespace internal {
+// An object that wraps a pointer to a C++ object and optionally deletes it
+// when the managed wrapper object is garbage collected.
+template <class CppType>
+class Managed : public Foreign {
+ public:
+  V8_INLINE CppType* get() {
+    return reinterpret_cast<CppType*>(foreign_address());
+  }
+
+  static Handle<Managed<CppType>> New(Isolate* isolate, CppType* ptr,
+                                      bool delete_on_gc = true) {
+    Handle<Foreign> foreign =
+        isolate->factory()->NewForeign(reinterpret_cast<Address>(ptr));
+    Handle<Managed<CppType>> handle(
+        reinterpret_cast<Managed<CppType>*>(*foreign), isolate);
+    if (delete_on_gc) {
+      RegisterWeakCallbackForDelete(isolate, handle);
+    }
+    return handle;
+  }
+
+ private:
+  static void RegisterWeakCallbackForDelete(Isolate* isolate,
+                                            Handle<Managed<CppType>> handle) {
+    Handle<Object> global_handle = isolate->global_handles()->Create(*handle);
+    GlobalHandles::MakeWeak(global_handle.location(), global_handle.location(),
+                            &Managed<CppType>::Delete,
+                            v8::WeakCallbackType::kFinalizer);
+  }
+  static void Delete(const v8::WeakCallbackInfo<void>& data) {
+    Managed<CppType>** p =
+        reinterpret_cast<Managed<CppType>**>(data.GetParameter());
+    delete (*p)->get();
+    GlobalHandles::Destroy(reinterpret_cast<Object**>(p));
+  }
+};
+}  // namespace internal
+}  // namespace v8
+
+#endif  // V8_WASM_MANAGED_H_