From ea219954e5937ac8bae49a811280f6822d84ecb6 Mon Sep 17 00:00:00 2001
From: "Mark S. Miller" <erights@gmail.com>
Date: Mon, 17 Apr 2023 21:35:55 -0700
Subject: [PATCH] refactor: stateShape causes accessor sharing

---
 .../src/virtualObjectManager.js               | 80 ++++++++++---------
 1 file changed, 43 insertions(+), 37 deletions(-)

diff --git a/packages/swingset-liveslots/src/virtualObjectManager.js b/packages/swingset-liveslots/src/virtualObjectManager.js
index 67141c7b5e7c..6aedfe96dd49 100644
--- a/packages/swingset-liveslots/src/virtualObjectManager.js
+++ b/packages/swingset-liveslots/src/virtualObjectManager.js
@@ -4,7 +4,7 @@
 import { assert, Fail } from '@agoric/assert';
 import { assertPattern, mustMatch } from '@agoric/store';
 import { defendPrototype, defendPrototypeKit } from '@endo/exo/tools.js';
-import { Far, hasOwnPropertyOf, passStyleOf } from '@endo/marshal';
+import { Far, passStyleOf } from '@endo/marshal';
 import { Nat } from '@endo/nat';
 import { parseVatSlot, makeBaseRef } from './parseVatSlots.js';
 import { enumerateKeysWithPrefix } from './vatstore-iterators.js';
@@ -13,7 +13,7 @@ import { assessFacetiousness } from './facetiousness.js';
 
 /** @template T @typedef {import('@agoric/vat-data').DefineKindOptions<T>} DefineKindOptions */
 
-const { defineProperty, getOwnPropertyNames } = Object;
+const { hasOwn, defineProperty, getOwnPropertyNames } = Object;
 const { ownKeys } = Reflect;
 const { quote: q } = assert;
 
@@ -742,6 +742,7 @@ export const makeVirtualObjectManager = (
     } = options;
 
     let facetNames; // undefined or a list of strings
+    const statePrototype = {}; // Not frozen yet
 
     // 'multifaceted' tells us which API was used: define[Durable]Kind
     // vs define[Durable]KindMulti. This function checks whether
@@ -817,15 +818,16 @@ export const makeVirtualObjectManager = (
       saveDurableKindDescriptor(durableKindDescriptor);
     }
 
-    let checkStateProperty = _prop => undefined;
+    let checkStateProperty = _prop => {};
     /** @type {(value: any, prop: string) => void} */
-    let checkStatePropertyValue = (_value, _prop) => undefined;
+    let checkStatePropertyValue = (_value, _prop) => {};
     if (stateShape) {
-      checkStateProperty = prop =>
-        hasOwnPropertyOf(stateShape, prop) ||
-        Fail`State must only have fields described by stateShape: ${q(
-          ownKeys(stateShape),
-        )}`;
+      checkStateProperty = prop => {
+        hasOwn(stateShape, prop) ||
+          Fail`State must only have fields described by stateShape: ${q(
+            ownKeys(stateShape),
+          )}`;
+      };
       checkStatePropertyValue = (value, prop) => {
         checkStateProperty(prop);
         mustMatch(value, stateShape[prop]);
@@ -854,37 +856,41 @@ export const makeVirtualObjectManager = (
     // * when state.prop is written, invoking the setter
     // This will cause a syscall.vatstoreGet only once per crank.
 
+    const makeFieldDescriptor = (prop, baseRef) => {
+      return harden({
+        get: () => {
+          const { valueMap, capdatas } = dataCache.get(baseRef);
+          if (!valueMap.has(prop)) {
+            const value = harden(unserialize(capdatas[prop]));
+            checkStatePropertyValue(value, prop);
+            valueMap.set(prop, value);
+          }
+          return valueMap.get(prop);
+        },
+        set: value => {
+          checkStatePropertyValue(value, prop);
+          const capdata = serialize(value);
+          assertAcceptableSyscallCapdataSize([capdata]);
+          if (isDurable) {
+            insistDurableCapdata(vrm, prop, capdata, true);
+          }
+          const record = dataCache.get(baseRef); // mutable
+          const oldSlots = record.capdatas[prop].slots;
+          const newSlots = capdata.slots;
+          vrm.updateReferenceCounts(oldSlots, newSlots);
+          record.capdatas[prop] = capdata; // modify in place ..
+          record.valueMap.set(prop, value);
+          dataCache.set(baseRef, record); // .. but mark as dirty
+        },
+        enumerable: true,
+      });
+    };
+
     const makeState = baseRef => {
-      const state = {};
+      const state = { __proto__: statePrototype };
       for (const prop of getOwnPropertyNames(dataCache.get(baseRef).capdatas)) {
         checkStateProperty(prop);
-        defineProperty(state, prop, {
-          get: () => {
-            const { valueMap, capdatas } = dataCache.get(baseRef);
-            if (!valueMap.has(prop)) {
-              const value = harden(unserialize(capdatas[prop]));
-              checkStatePropertyValue(value, prop);
-              valueMap.set(prop, value);
-            }
-            return valueMap.get(prop);
-          },
-          set: value => {
-            checkStatePropertyValue(value, prop);
-            const capdata = serialize(value);
-            assertAcceptableSyscallCapdataSize([capdata]);
-            if (isDurable) {
-              insistDurableCapdata(vrm, prop, capdata, true);
-            }
-            const record = dataCache.get(baseRef); // mutable
-            const oldSlots = record.capdatas[prop].slots;
-            const newSlots = capdata.slots;
-            vrm.updateReferenceCounts(oldSlots, newSlots);
-            record.capdatas[prop] = capdata; // modify in place ..
-            record.valueMap.set(prop, value);
-            dataCache.set(baseRef, record); // .. but mark as dirty
-          },
-          enumerable: true,
-        });
+        defineProperty(state, prop, makeFieldDescriptor(prop, baseRef));
       }
       return harden(state);
     };