feat: refactor object pinning

Author: FUDCo

packages/SwingSet/src/controller.js

@@ -22,7 +22,6 @@ import { waitUntilQuiescent } from './waitUntilQuiescent.js';
 import { makeGcAndFinalize } from './gc-and-finalize.js';
 import { insistStorageAPI } from './storageAPI.js';
 import { insistCapData } from './capdata.js';
-import { parseVatSlot } from './parseVatSlots.js';
 import { provideHostStorage } from './hostStorage.js';
 import {
   swingsetIsInitialized,
@@ -361,6 +360,12 @@ export async function makeSwingsetController(
       return defensiveCopy(kernel.getStatus());
     },
 
+    pinVatRoot(vatName) {
+      const vatID = kernel.vatNameToID(vatName);
+      const kref = kernel.getRootObject(vatID);
+      kernel.pinObject(kref);
+    },
+
     // these are for tests
 
     kpStatus(kpid) {
@@ -379,17 +384,15 @@ export async function makeSwingsetController(
 
     /**
      * @param {string} vatName
-     * @param {string} exportID
      * @param {string} method
      * @param {CapData<unknown>} args
      * @param {ResolutionPolicy} resultPolicy
      */
-    queueToVatExport(vatName, exportID, method, args, resultPolicy = 'ignore') {
+    queueToVatRoot(vatName, method, args, resultPolicy = 'ignore') {
       const vatID = kernel.vatNameToID(vatName);
-      parseVatSlot(exportID);
       assert.typeof(method, 'string');
       insistCapData(args);
-      const kref = kernel.addExport(vatID, exportID);
+      const kref = kernel.getRootObject(vatID);
       const kpid = kernel.queueToKref(kref, method, args, resultPolicy);
       if (kpid) {
         kernel.kpRegisterInterest(kpid);

packages/SwingSet/src/kernel/initializeKernel.js

@@ -8,7 +8,7 @@ import { makeVatSlot } from '../parseVatSlots';
 import { insistStorageAPI } from '../storageAPI';
 import { wrapStorage } from './state/storageWrapper';
 import makeKernelKeeper from './state/kernelKeeper';
-import { doAddExport, doQueueToKref } from './kernel';
+import { exportRootObject, doQueueToKref } from './kernel';
 
 function makeVatRootObjectSlot() {
   return makeVatSlot('object', true, 0);
@@ -82,11 +82,10 @@ export function initializeKernel(config, hostStorage, verbose = false) {
       vatKeeper.setSourceAndOptions({ bundle, bundleName }, creationOptions);
       if (name === 'vatAdmin') {
         // Create a kref for the vatAdmin root, so the kernel can tell it
-        // about creation/termination of dynamic vats. doAddExport will
-        // increment the refcount so it won't go away, despite being
-        // unreferenced by any other vat.
-        const rootVref = makeVatRootObjectSlot();
-        const kref = doAddExport(kernelKeeper, vatID, rootVref);
+        // about creation/termination of dynamic vats.
+        const kref = exportRootObject(kernelKeeper, vatID);
+        // Pin, to prevent it being GC'd when only the kvStore points to it
+        kernelKeeper.pinObject(kref);
         kvStore.set('vatAdminRootKref', kref);
         gotVatAdminRootKref = true;
       }
@@ -193,8 +192,7 @@ export function initializeKernel(config, hostStorage, verbose = false) {
     });
     const args = harden([vatObj0s, deviceObj0s]);
     // doQueueToKref() takes kernel-refs (ko+NN, kd+NN) in s.slots
-    const rootVref = makeVatRootObjectSlot();
-    const rootKref = doAddExport(kernelKeeper, bootstrapVatID, rootVref);
+    const rootKref = exportRootObject(kernelKeeper, bootstrapVatID);
     const resultKpid = doQueueToKref(
       kernelKeeper,
       rootKref,

packages/SwingSet/src/kernel/kernel.js

@@ -20,7 +20,7 @@ import { makeSlogger, makeDummySlogger } from './slogger.js';
 import { getKpidsToRetire } from './cleanup.js';
 import { processNextGCAction } from './gc-actions.js';
 
-import { makeVatRootObjectSlot, makeVatLoader } from './loadVat.js';
+import { makeVatLoader } from './loadVat.js';
 import { makeDeviceTranslators } from './deviceTranslator.js';
 import { notifyTermination } from './notifyTermination.js';
 
@@ -43,6 +43,20 @@ function makeError(message, name = 'Error') {
 
 const VAT_TERMINATION_ERROR = makeError('vat terminated');
 
+/**
+ * Provide the kref of a vat's root object, as if it had been exported.
+ *
+ * @param {*} kernelKeeper  Kernel keeper managing persistent kernel state.
+ * @param {string} vatID  Vat ID of the vat whose root kref is sought.
+ *
+ * @returns {string} the kref of the root object of the given vat.
+ */
+export function exportRootObject(kernelKeeper, vatID) {
+  insistVatID(vatID);
+  const vatKeeper = kernelKeeper.provideVatKeeper(vatID);
+  return vatKeeper.mapVatSlotToKernelSlot('o+0');
+}
+
 /*
  * Pretend that a vat just exported an object, and increment the refcount on
  * the resulting kref so nothing tries to delete it for being unreferenced.
@@ -60,8 +74,7 @@ export function doAddExport(kernelKeeper, fromVatID, vref) {
 
 /**
  * Enqueue a message to some kernel object, as if the message had been sent
- * by some other vat. This requires a kref as a target, so use e.g.
- * doAddExport to acquire one and increment its refcount to keep it alive.
+ * by some other vat. This requires a kref as a target.
  *
  * @param {*} kernelKeeper  Kernel keeper managing persistent kernel state
  * @param {string} kref  Target of the message
@@ -236,6 +249,10 @@ export default function buildKernel(
     return vatKeeper.mapKernelSlotToVatSlot(kernelSlot);
   }
 
+  function pinObject(kref) {
+    kernelKeeper.pinObject(kref);
+  }
+
   function addExport(fromVatID, vatSlot) {
     if (!started) {
       throw new Error('must do kernel.start() before addExport()');
@@ -576,7 +593,7 @@ export default function buildKernel(
     function makeSuccessResponse() {
       // build success message, giving admin vat access to the new vat's root
       // object
-      const kernelRootObjSlot = addExport(vatID, makeVatRootObjectSlot());
+      const kernelRootObjSlot = exportRootObject(kernelKeeper, vatID);
       return {
         body: JSON.stringify([
           vatID,
@@ -1068,6 +1085,10 @@ export default function buildKernel(
 
     addImport,
     addExport,
+    getRootObject(vatID) {
+      return exportRootObject(kernelKeeper, vatID);
+    },
+    pinObject,
     vatNameToID,
     deviceNameToID,
     queueToKref,

packages/SwingSet/src/kernel/state/kernelKeeper.js

@@ -63,6 +63,7 @@ const enableKernelGC = true;
 
 // runQueue = JSON(runQueue) // usually empty on disk
 // gcActions = JSON(gcActions) // usually empty on disk
+// pinnedObjects = ko$NN[,ko$NN..]
 
 // ko.nextID = $NN
 // ko$NN.owner = $vatID
@@ -1055,6 +1056,16 @@ export default function makeKernelKeeper(
     return importers;
   }
 
+  function pinObject(kref) {
+    const pinList = kvStore.get('pinnedObjects') || '';
+    const pinned = new Set(commaSplit(pinList));
+    if (!pinned.has(kref)) {
+      incrementRefCount(kref, 'pin');
+      pinned.add(kref);
+      kvStore.set('pinnedObjects', [...pinned].sort().join(','));
+    }
+  }
+
   // used for debugging, and tests. This returns a JSON-serializable object.
   // It includes references to live (mutable) kernel state, so don't mutate
   // the pieces, and be sure to serialize/deserialize before passing it
@@ -1173,6 +1184,7 @@ export default function makeKernelKeeper(
     kernelObjectExists,
     getImporters,
     deleteKernelObject,
+    pinObject,
 
     addKernelPromise,
     addKernelPromiseForVat,

packages/swingset-runner/src/main.js

@@ -411,6 +411,7 @@ export async function main() {
       config,
       bootstrapArgv,
       hostStorage,
+      { verbose },
       runtimeOptions,
     );
     swingStore.commit();
@@ -424,6 +425,11 @@ export async function main() {
     deviceEndowments,
     runtimeOptions,
   );
+  if (benchmarkRounds > 0) {
+    // Pin the vat root that will run benchmark rounds so it'll still be there
+    // when it comes time to run them.
+    controller.pinVatRoot(launchIndirectly ? 'launcher' : 'bootstrap');
+  }
 
   let blockNumber = 0;
   let statLogger = null;
@@ -560,9 +566,8 @@ export async function main() {
     let totalSteps = 0;
     let totalDeltaT = 0n;
     for (let i = 0; i < rounds; i += 1) {
-      const roundResult = controller.queueToVatExport(
+      const roundResult = controller.queueToVatRoot(
         launchIndirectly ? 'launcher' : 'bootstrap',
-        'o+0',
         'runBenchmarkRound',
         args,
         'ignore',