C++ 插件


Node.js 插件是用 C++ 编写的动态链接共享对象,可以使用 require() 函数加载到 Node.js 中,且像普通的 Node.js 模块一样被使用。 它们主要用于为运行在 Node.js 中的 JavaScript 与 C/C++ 库之间提供接口。

目前用于实现插件的方法相当复杂,涉及多个组件和 API 的知识:

  • V8:Node.js 目前用于提供 JavaScript 实现的 C++ 库。 V8 提供了用于创建对象、调用函数等的机制。 V8 的 API 文档主要在 v8.h 头文件中(Node.js 源代码中的 deps/v8/include/v8.h),也可以在查看 V8 在线文档

  • libuv:实现了 Node.js 的事件循环、工作线程、以及平台所有的的异步操作的 C 库。 它也是一个跨平台的抽象库,使所有主流操作系统中可以像 POSIX 一样访问常用的系统任务,比如与文件系统、socket、定时器、以及系统事件的交互。 libuv 还提供了一个类似 POSIX 多线程的线程抽象,可被用于强化更复杂的需要超越标准事件循环的异步插件。 建议插件开发者多思考如何通过在 libuv 的非阻塞系统操作、工作线程、或自定义的 libuv 线程中降低工作负载来避免在 I/O 或其他时间密集型任务中阻塞事件循环。

  • 内置的 Node.js 库。Node.js 自身开放了一些插件可以使用的 C++ API。 其中最重要的是 node::ObjectWrap 类。

  • Node.js 包含一些其他的静态链接库,如 OpenSSL。 这些库位于 Node.js 源代码中的 deps/ 目录。 只有 V8 和 OpenSSL 符号是被 Node.js 开放的,并且通过插件被用于不同的场景。 更多信息可查看 链接到 Node.js 自身的依赖

以下例子可从 Node 插件示例 下载,作为学习插件开发的起点。

Node.js Addons are dynamically-linked shared objects, written in C++, that can be loaded into Node.js using the require() function, and used just as if they were an ordinary Node.js module. They are used primarily to provide an interface between JavaScript running in Node.js and C/C++ libraries.

At the moment, the method for implementing Addons is rather complicated, involving knowledge of several components and APIs:

  • V8: the C++ library Node.js currently uses to provide the JavaScript implementation. V8 provides the mechanisms for creating objects, calling functions, etc. V8's API is documented mostly in the v8.h header file (deps/v8/include/v8.h in the Node.js source tree), which is also available online.

  • libuv: The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the filesystem, sockets, timers, and system events. libuv also provides a pthreads-like threading abstraction that may be used to power more sophisticated asynchronous Addons that need to move beyond the standard event loop. Addon authors are encouraged to think about how to avoid blocking the event loop with I/O or other time-intensive tasks by off-loading work via libuv to non-blocking system operations, worker threads or a custom use of libuv's threads.

  • Internal Node.js libraries. Node.js itself exports a number of C++ APIs that Addons can use — the most important of which is the node::ObjectWrap class.

  • Node.js includes a number of other statically linked libraries including OpenSSL. These other libraries are located in the deps/ directory in the Node.js source tree. Only the libuv, OpenSSL, V8 and zlib symbols are purposefully re-exported by Node.js and may be used to various extents by Addons. See Linking to Node.js' own dependencies for additional information.

All of the following examples are available for download and may be used as the starting-point for an Addon.