[wasm] WebAssembly.Memory object can be referenced by multiple Instance objects.

src/wasm/wasm-objects.cc

Index: src/wasm/wasm-objects.cc
diff --git a/src/wasm/wasm-objects.cc b/src/wasm/wasm-objects.cc
index 717696dabcfc2a2f12bac3eb98c6c03a02cc184b..fbe64eb6159c89054b3066e26919d7e793418e02 100644
--- a/src/wasm/wasm-objects.cc
+++ b/src/wasm/wasm-objects.cc
@@ -174,7 +174,8 @@ Handle<WasmMemoryObject> WasmMemoryObject::New(Isolate* isolate,
                                                int maximum) {
   Handle<JSFunction> memory_ctor(
       isolate->native_context()->wasm_memory_constructor());
-  Handle<JSObject> memory_obj = isolate->factory()->NewJSObject(memory_ctor);
+  Handle<JSObject> memory_obj =
+      isolate->factory()->NewJSObject(memory_ctor, TENURED);
   memory_obj->SetInternalField(kArrayBuffer, *buffer);
   memory_obj->SetInternalField(kMaximum,
                                static_cast<Object*>(Smi::FromInt(maximum)));
@@ -184,6 +185,8 @@ Handle<WasmMemoryObject> WasmMemoryObject::New(Isolate* isolate,
 }
 
 DEFINE_ACCESSORS(WasmMemoryObject, buffer, kArrayBuffer, JSArrayBuffer)
+DEFINE_OPTIONAL_ACCESSORS(WasmMemoryObject, instances_link, kInstancesLink,
+                          WasmInstanceWrapper)
 
 uint32_t WasmMemoryObject::current_pages() {
   return SafeUint32(get_buffer()->byte_length()) / wasm::WasmModule::kPageSize;
@@ -199,10 +202,26 @@ WasmMemoryObject* WasmMemoryObject::cast(Object* object) {
   return reinterpret_cast<WasmMemoryObject*>(object);
 }
 
-void WasmMemoryObject::AddInstance(WasmInstanceObject* instance) {
-  // TODO(gdeepti): This should be a weak list of instance objects
-  // for instances that share memory.
-  SetInternalField(kInstance, instance);
+void WasmMemoryObject::AddInstance(Isolate* isolate,
+                                   Handle<WasmInstanceObject> instance) {
+  Handle<WasmInstanceWrapper> instance_wrapper;
+  if (has_instances_link()) {
+    Handle<WasmInstanceWrapper> current_wrapper(get_instances_link());
+    DCHECK(WasmInstanceWrapper::IsWasmInstanceWrapper(*current_wrapper));
+    DCHECK(!current_wrapper->has_previous());
+    instance_wrapper = WasmInstanceWrapper::New(isolate, instance);
+    instance_wrapper->set_next_wrapper(*current_wrapper);
+    current_wrapper->set_previous_wrapper(*instance_wrapper);
+  } else {
+    instance_wrapper = WasmInstanceWrapper::New(isolate, instance);
+  }
+  set_instances_link(*instance_wrapper);
+  instance->set_instance_wrapper(*instance_wrapper);
+}
+
+void WasmMemoryObject::ResetInstancesLink(Isolate* isolate) {
+  Handle<Object> undefined = isolate->factory()->undefined_value();
+  SetInternalField(kInstancesLink, *undefined);
 }
 
 DEFINE_ACCESSORS(WasmInstanceObject, compiled_module, kCompiledModule,
@@ -215,6 +234,8 @@ DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, memory_object, kMemoryObject,
                           WasmMemoryObject)
 DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, debug_info, kDebugInfo,
                           WasmDebugInfo)
+DEFINE_OPTIONAL_ACCESSORS(WasmInstanceObject, instance_wrapper,
+                          kWasmMemInstanceWrapper, WasmInstanceWrapper)
 
 WasmModuleObject* WasmInstanceObject::module_object() {
   return WasmModuleObject::cast(*get_compiled_module()->wasm_module());
@@ -424,3 +445,34 @@ bool WasmCompiledModule::GetPositionInfo(uint32_t position,
   info->line_end = function.code_end_offset;
   return true;
 }
+
+Handle<WasmInstanceWrapper> WasmInstanceWrapper::New(
+    Isolate* isolate, Handle<WasmInstanceObject> instance) {
+  Handle<FixedArray> array =
+      isolate->factory()->NewFixedArray(kWrapperPropertyCount, TENURED);
+  Handle<WasmInstanceWrapper> instance_wrapper(
+      reinterpret_cast<WasmInstanceWrapper*>(*array), isolate);
+  instance_wrapper->set_instance_object(instance, isolate);
+  return instance_wrapper;
+}
+
+bool WasmInstanceWrapper::IsWasmInstanceWrapper(Object* obj) {
+  if (!obj->IsFixedArray()) return false;
+  Handle<FixedArray> array = handle(FixedArray::cast(obj));
+  if (array->length() != kWrapperPropertyCount) return false;
+  if (!array->get(kWrapperInstanceObject)->IsWeakCell()) return false;
+  Isolate* isolate = array->GetIsolate();
+  if (!array->get(kNextInstanceWrapper)->IsUndefined(isolate) &&
+      !array->get(kNextInstanceWrapper)->IsFixedArray())
+    return false;
+  if (!array->get(kPreviousInstanceWrapper)->IsUndefined(isolate) &&
+      !array->get(kPreviousInstanceWrapper)->IsFixedArray())
+    return false;
+  return true;
+}
+
+void WasmInstanceWrapper::set_instance_object(Handle<JSObject> instance,
+                                              Isolate* isolate) {
+  Handle<WeakCell> cell = isolate->factory()->NewWeakCell(instance);
+  set(kWrapperInstanceObject, *cell);
+}