vm: implement vm.measureMemory() for per-context memory measurement

This patch implements `vm.measureMemory()` with the new
`v8::Isolate::MeasureMemory()` API to measure per-context memory
usage. This should be experimental, since detailed memory
measurement requires further integration with the V8 API
that should be available in a future V8 update.

doc/api/vm.md

@@ -295,6 +295,55 @@ console.log(globalVar);
 // 1000
 ```
 
+## `vm.measureMemory([options, [contextifiedObject]])`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Measure the memory used by the current execution context or a specified context.
+
+* `options` {Object} Optional.
+  * `mode` {vm.constants.measureMemory.mode}
+    **Default:** `vm.constants.measureMemory.mode.SUMMARY`
+* `contextifiedObject` {Object} Optional. A [contextified][] object returned
+  by `vm.createContext()`. If not specified, measure the memory usage of the
+  current context where `vm.measureMemory()` is invoked.
+* Returns: {Promise} If the memory is successfully measured the promise will
+  resolve with an object containing information about the memory usage.
+
+The format of the object that the returned Promise may resolve with is
+specific to the V8 engine and may change from one version of V8 to the next.
+
+The returned result is different from the statistics returned by
+`v8.GetHeapSpaceStatistics()` in that `vm.measureMemory()` measures
+the memory reachable from a specific context, while
+`v8.GetHeapSpaceStatistics()` measures the memory used by an instance
+of V8 engine, which can switch among multiple contexts that reference
+objects in the heap of one engine.
+
+```js
+const vm = require('vm');
+// Measure the memory used by the current context and return the result
+// in summary.
+vm.measureMemory({ mode: vm.constants.measureMemory.mode.SUMMARY })
+  // Is the same as vm.measureMemory()
+  .then((result) => {
+    // The current format is:
+    // { total: { jsMemoryEstimate: 2211728, jsMemoryRange: [ 0, 2211728 ] } }
+    console.log(result);
+  });
+
+const context = vm.createContext({});
+vm.measureMemory({ mode: vm.constants.measureMemory.mode.DETAILED }, context)
+  .then((result) => {
+    // At the moment the DETAILED format is the same as the SUMMARY one.
+    console.log(result);
+  });
+```
+
 ## Class: `vm.Module`
 <!-- YAML
 added: v13.0.0
@@ -1169,6 +1218,26 @@ the `process.nextTick()` and `queueMicrotask()` functions.
 This issue occurs because all contexts share the same microtask and nextTick
 queues.
 
+## `vm.constants`
+<!-- YAML
+added: REPLACEME
+-->
+
+* {Object} An object containing commonly used constants for the vm module.
+
+### `vm.constants.measureMemory`
+<!-- YAML
+added: REPLACEME
+-->
+
+> Stability: 1 - Experimental
+
+Constants to be used with the [`vm.measureMemory()`][] method.
+
+* `mode` {Object}
+  * `SUMMARY` {integer} Return the measured memory in summary.
+  * `DETAILED` {integer} Return the measured memory in detail.
+
 [`ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING`]: errors.html#ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING
 [`ERR_VM_MODULE_STATUS`]: errors.html#ERR_VM_MODULE_STATUS
 [`Error`]: errors.html#errors_class_error
@@ -1178,6 +1247,7 @@ queues.
 [`script.runInThisContext()`]: #vm_script_runinthiscontext_options
 [`url.origin`]: url.html#url_url_origin
 [`vm.createContext()`]: #vm_vm_createcontext_contextobject_options
+[`vm.measureMemory()`]: #vm_vm_measurememory_options_contextifiedobject
 [`vm.runInContext()`]: #vm_vm_runincontext_code_contextifiedobject_options
 [`vm.runInThisContext()`]: #vm_vm_runinthiscontext_code_options
 [Cyclic Module Record]: https://tc39.es/ecma262/#sec-cyclic-module-records

lib/vm.js

@@ -30,7 +30,9 @@ const {
   ContextifyScript,
   makeContext,
   isContext: _isContext,
-  compileFunction: _compileFunction
+  constants,
+  compileFunction: _compileFunction,
+  measureMemory: _measureMemory,
 } = internalBinding('contextify');
 const {
   ERR_INVALID_ARG_TYPE,
@@ -47,7 +49,10 @@ const {
   validateBuffer,
   validateObject,
 } = require('internal/validators');
-const { kVmBreakFirstLineSymbol } = require('internal/util');
+const {
+  kVmBreakFirstLineSymbol,
+  emitExperimentalWarning
+} = require('internal/util');
 const kParsingContext = Symbol('script parsing context');
 
 class Script extends ContextifyScript {
@@ -355,6 +360,25 @@ function compileFunction(code, params, options = {}) {
   return result.function;
 }
 
+function measureMemory(options = {}, context) {
+  emitExperimentalWarning('vm.measureMemory');
+  validateObject(options, 'options');
+  let mode = options.mode;
+  if (mode === undefined) {
+    mode = constants.measureMemory.mode.SUMMARY;
+  }
+  validateInt32(mode, 'options.mode',
+                constants.measureMemory.mode.SUMMARY,
+                constants.measureMemory.mode.DETAILED);
+  if (context === undefined) {
+    return _measureMemory(mode);
+  }
+  if (typeof context !== 'object' || context === null ||
+        !_isContext(context)) {
+    throw new ERR_INVALID_ARG_TYPE('contextifiedObject', 'vm.Context', context);
+  }
+  return _measureMemory(mode, context);
+}
 
 module.exports = {
   Script,
@@ -365,6 +389,8 @@ module.exports = {
   runInThisContext,
   isContext,
   compileFunction,
+  measureMemory,
+  constants,
 };
 
 if (require('internal/options').getOptionValue('--experimental-vm-modules')) {

src/node_contextify.cc

@@ -47,17 +47,20 @@ using v8::FunctionCallbackInfo;
 using v8::FunctionTemplate;
 using v8::HandleScope;
 using v8::IndexedPropertyHandlerConfiguration;
+using v8::Int32;
 using v8::Integer;
 using v8::Isolate;
 using v8::Local;
 using v8::Maybe;
 using v8::MaybeLocal;
+using v8::MeasureMemoryMode;
 using v8::Name;
 using v8::NamedPropertyHandlerConfiguration;
 using v8::Number;
 using v8::Object;
 using v8::ObjectTemplate;
 using v8::PrimitiveArray;
+using v8::Promise;
 using v8::PropertyAttribute;
 using v8::PropertyCallbackInfo;
 using v8::PropertyDescriptor;
@@ -1200,11 +1203,38 @@ static void WatchdogHasPendingSigint(const FunctionCallbackInfo<Value>& args) {
   args.GetReturnValue().Set(ret);
 }
 
+static void MeasureMemory(const FunctionCallbackInfo<Value>& args) {
+  CHECK(args[0]->IsInt32());
+  int32_t mode = args[0].As<v8::Int32>()->Value();
+  Isolate* isolate = args.GetIsolate();
+  Environment* env = Environment::GetCurrent(args);
+  Local<Context> context;
+  if (args[1]->IsUndefined()) {
+    context = isolate->GetCurrentContext();
+  } else {
+    ContextifyContext* sandbox =
+        ContextifyContext::ContextFromContextifiedSandbox(env,
+                                                          args[1].As<Object>());
+    CHECK_NOT_NULL(sandbox);
+    context = sandbox->context();
+    if (context.IsEmpty()) {  // Not yet fully initilaized
+      return;
+    }
+  }
+  v8::Local<v8::Promise> promise;
+  if (!isolate->MeasureMemory(context, static_cast<v8::MeasureMemoryMode>(mode))
+           .ToLocal(&promise)) {
+    return;
+  }
+  args.GetReturnValue().Set(promise);
+}
+
 void Initialize(Local<Object> target,
                 Local<Value> unused,
                 Local<Context> context,
                 void* priv) {
   Environment* env = Environment::GetCurrent(context);
+  Isolate* isolate = env->isolate();
   ContextifyContext::Init(env, target);
   ContextifyScript::Init(env, target);
 
@@ -1221,6 +1251,19 @@ void Initialize(Local<Object> target,
 
     env->set_compiled_fn_entry_template(tpl->InstanceTemplate());
   }
+
+  Local<Object> constants = Object::New(env->isolate());
+  Local<Object> measure_memory = Object::New(env->isolate());
+  Local<Object> memory_mode = Object::New(env->isolate());
+  MeasureMemoryMode SUMMARY = MeasureMemoryMode::kSummary;
+  MeasureMemoryMode DETAILED = MeasureMemoryMode::kDetailed;
+  NODE_DEFINE_CONSTANT(memory_mode, SUMMARY);
+  NODE_DEFINE_CONSTANT(memory_mode, DETAILED);
+  READONLY_PROPERTY(measure_memory, "mode", memory_mode);
+  READONLY_PROPERTY(constants, "measureMemory", measure_memory);
+  target->Set(context, env->constants_string(), constants).Check();
+
+  env->SetMethod(target, "measureMemory", MeasureMemory);
 }
 
 }  // namespace contextify

test/parallel/test-vm-measure-memory.js

@@ -0,0 +1,73 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const vm = require('vm');
+const {
+  SUMMARY,
+  DETAILED
+} = vm.constants.measureMemory.mode;
+
+common.expectWarning('ExperimentalWarning',
+                     'vm.measureMemory is an experimental feature. ' +
+                     'This feature could change at any time');
+
+// Test measuring memory of the current context
+{
+  vm.measureMemory(undefined)
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({})
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({ mode: SUMMARY })
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({ mode: DETAILED })
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  assert.throws(() => vm.measureMemory(null), {
+    code: 'ERR_INVALID_ARG_TYPE'
+  });
+  assert.throws(() => vm.measureMemory('summary'), {
+    code: 'ERR_INVALID_ARG_TYPE'
+  });
+  assert.throws(() => vm.measureMemory({ mode: -1 }), {
+    code: 'ERR_OUT_OF_RANGE'
+  });
+}
+
+// Test measuring memory of the sandbox
+{
+  const sandbox = vm.createContext();
+  vm.measureMemory(undefined, sandbox)
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({}, sandbox)
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({ mode: SUMMARY }, sandbox)
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  vm.measureMemory({ mode: DETAILED }, sandbox)
+    .then((result) => {
+      assert(result instanceof Object);
+    });
+
+  assert.throws(() => vm.measureMemory({ mode: SUMMARY }, null), {
+    code: 'ERR_INVALID_ARG_TYPE'
+  });
+}

tools/doc/type-parser.js

@@ -149,6 +149,7 @@ const customTypesMap = {
 
   'vm.Module': 'vm.html#vm_class_vm_module',
   'vm.SourceTextModule': 'vm.html#vm_class_vm_sourcetextmodule',
+  'vm.constants.measureMemory.mode': 'vm.html#vm_vm_constants_measurememory',
 
   'MessagePort': 'worker_threads.html#worker_threads_class_messageport',