[wasm] Managed<T> ensures T's lifetime does not leak past Isolate's

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"
-
-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 Managed<CppType>* cast(Object* obj) {
-    SLOW_DCHECK(obj->IsForeign());
-    return reinterpret_cast<Managed<CppType>*>(obj);
-  }
-
-  static Handle<Managed<CppType>> New(Isolate* isolate, CppType* ptr,
-                                      bool delete_on_gc = true) {
-    Handle<Managed<CppType>> handle = Handle<Managed<CppType>>::cast(
-        isolate->factory()->NewForeign(reinterpret_cast<Address>(ptr)));
-    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();
-    (*p)->set_foreign_address(0);
-    GlobalHandles::Destroy(reinterpret_cast<Object**>(p));
-  }
-};
-}  // namespace internal
-}  // namespace v8
-
-#endif  // V8_WASM_MANAGED_H_