Context-sensitive examples are not extensible

未關閉
  • 哪裡不對？
#171 0 則留言 0 個 reaction 已指派 0 人 在 GitHub 檢視

還沒有人認領這個 Issue。

評估

難度
4/5
預估耗時
3-5 天
新手友好度
35/100
Issue 類型
缺陷
描述清晰度
基本清楚
活躍度
停滯
技術堆疊
cpp, nodejs
領域
api, developer-experience

研究方向

Start with the test.cc and test.js reproducer, then read the N-API SetInstanceData documentation cited in the issue. Verify how creating Foo and Bar causes the second instance-data value to replace the first. Done means both createFoo() and createBar() produce objects passing their respective instanceof checks without leaking the earlier constructor reference.

由索引模型根據 Issue 內容生成。

描述

This pull request https://github.com/nodejs/node-addon-examples/pull/139 removes global static references from the examples. However, proposed solution works only for single object wrap.

Consider the following example where two object wraps are created using the same code snippet:

Napi::FunctionReference* constructor = new Napi::FunctionReference();
*constructor = Napi::Persistent(func);
env.SetInstanceData(constructor);

test.cc

#include <napi.h>

#include <cassert>

class Foo : public Napi::ObjectWrap<Foo> {
 public:
  static void Init(Napi::Env env, Napi::Object exports) {
    Napi::Function func = DefineClass(env, "Foo", {});

    Napi::FunctionReference* constructor = new Napi::FunctionReference();
    *constructor = Napi::Persistent(func);
    env.SetInstanceData(constructor);

    exports.Set("Foo", func);
  }

  static Napi::Object NewInstance(Napi::Env env) {
    const auto constructor = env.GetInstanceData<Napi::FunctionReference>();
    assert(constructor != nullptr);
    return constructor->New({});
  }

  explicit Foo(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Foo>{info} {}
};

class Bar : public Napi::ObjectWrap<Foo> {
 public:
  static void Init(Napi::Env env, Napi::Object exports) {
    Napi::Function func = DefineClass(env, "Bar", {});

    Napi::FunctionReference* constructor = new Napi::FunctionReference();
    *constructor = Napi::Persistent(func);
    env.SetInstanceData(constructor);

    exports.Set("Bar", func);
  }

  static Napi::Object NewInstance(Napi::Env env) {
    const auto constructor = env.GetInstanceData<Napi::FunctionReference>();
    assert(constructor != nullptr);
    return constructor->New({});
  }

  explicit Bar(const Napi::CallbackInfo& info) : Napi::ObjectWrap<Foo>{info} {}
};

Napi::Value CreateFoo(const Napi::CallbackInfo& info) {
  return Foo::NewInstance(info.Env());
}

Napi::Value CreateBar(const Napi::CallbackInfo& info) {
  return Bar::NewInstance(info.Env());
}

Napi::Object InitAll(Napi::Env env, Napi::Object exports) {
  Foo::Init(env, exports);
  Bar::Init(env, exports);
  exports.Set("createFoo", Napi::Function::New(env, CreateFoo));
  exports.Set("createBar", Napi::Function::New(env, CreateBar));
  return exports;
}

NODE_API_MODULE(NODE_GYP_MODULE_NAME, InitAll)

test.js

'use strict';

const assert = require('assert');
const {createFoo, createBar, Foo, Bar} = require('./build/Debug/test');

const foo = createFoo();
assert(foo instanceof Foo); // fails
const bar = createBar();
assert(bar instanceof Bar);

$ node test.js
assert.js:383
    throw err;
    ^

AssertionError [ERR_ASSERTION]: The expression evaluated to a falsy value:

  assert(foo instanceof Foo)

    at Object.<anonymous> (/home/kostya/tmp/napi-test/test.js:7:1)
    at Module._compile (internal/modules/cjs/loader.js:1063:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:1092:10)
    at Module.load (internal/modules/cjs/loader.js:928:32)
    at Function.Module._load (internal/modules/cjs/loader.js:769:14)
    at Function.executeUserEntryPoint [as runMain] (internal/modules/run_main.js:72:12)
    at internal/main/run_main_module.js:17:47 {
  generatedMessage: true,
  code: 'ERR_ASSERTION',
  actual: false,
  expected: true,
  operator: '=='
}

As we can see second call of Env::SetInstanceData() in Bar::Init() overrides reference to Foo constructor. Moreover, this causes memory leak, because destructor of the first reference will not be called

From https://nodejs.org/dist/latest-v14.x/docs/api/n-api.html#n_api_napi_set_instance_data

Any existing data associated with the currently running Agent which was set by means of a previous call to napi_set_instance_data() will be overwritten. If a finalize_cb was provided by the previous call, it will not be called.

主要語言
C++
星號
2.6k
分支
598
30 天內沒有已合併 PR

環境準備

從這裡開始

  1. 先讀完整個 Issue，再讀專案的貢獻指南。
  2. 在 Issue 下留言說明你要接手 —— 這能避免兩個人做同樣的事。
  3. Fork 儲存庫，在一個分支上完成修改。
  4. 送出 Pull Request，並在描述裡引用這個 Issue 編號。

nodejs/node-addon-examples 的其他 Issue

查看 nodejs/node-addon-examples 的全部 Issue

相似的 Issue

更多 C++ Issue

把新 issue 寄到你的電子郵件信箱

精選適合新手參與的 GitHub issue 摘要。