.12-浅析webpack源码之NodeWatchFileSystem模块…

2018-06-24 01:04:41来源:未知 阅读 ()

新老客户大回馈,云服务器低至5折

  剩下一个watch模块,这个模块比较深,先大概过一下整体涉及内容再分部讲解。

  流程图如下:

NodeWatchFileSystem

const Watchpack = require("watchpack");

class NodeWatchFileSystem {
    constructor(inputFileSystem) {
        this.inputFileSystem = inputFileSystem;
        this.watcherOptions = {
            aggregateTimeout: 0
        };
        this.watcher = new Watchpack(this.watcherOptions);
    }

    watch(
        files, /*Array*/
        dirs, /*Array*/
        missing, /*Array*/
        startTime, /*number*/
        options, /*object*/
        callback, /*function*/
        callbackUndelayed /*function*/
    ) {
        // params validate...
        const oldWatcher = this.watcher;
        // 生成Watchpack对象
        this.watcher = new Watchpack(options);
        if (callbackUndelayed)
            this.watcher.once("change", callbackUndelayed);
        this.watcher.once("aggregated", (changes, removals) => { /**/ });
        // 调用watch方法
        this.watcher.watch(files.concat(missing), dirs.concat(missing), startTime);
        if (oldWatcher) {
            oldWatcher.close();
        }
        return {
            close: () => { /**/ },
            pause: () => { /**/ }
        };
    }
}

module.exports = NodeWatchFileSystem;

  除去细节代码,该模块大体如下;

1、引入Watchpack模块

2、接受一个inputFileSystem作为构造函数的参数

3、根据配置选项实例化一个Watchpack类

4、核心watch方法为调用实例类的watch方法,传入给定参数,绑定两个一次性事件绑定并返回了一个对象

  模块核心的方法调用的是Watchpack实体类上的,所以需要进一步探究该类。

  该模块涉及到了nodejs的event模块,内容非常简单,这里就不做介绍了,详情可查看官网API:https://nodejs.org/dist/latest-v8.x/docs/api/events.html

 

Watchpack

var watcherManager = require("./watcherManager");
var EventEmitter = require("events").EventEmitter;
Watchpack.prototype = Object.create(EventEmitter.prototype);

class Watchpack {
    constructor(options) {
        EventEmitter.call(this);
        if (!options) options = {};
        if (!options.aggregateTimeout) options.aggregateTimeout = 200;
        this.options = options;
        this.watcherOptions = {
            ignored: options.ignored,
            poll: options.poll
        };
        this.fileWatchers = [];
        this.dirWatchers = [];
        this.mtimes = Object.create(null);
        this.paused = false;
        this.aggregatedChanges = [];
        this.aggregatedRemovals = [];
        this.aggregateTimeout = 0;
        this._onTimeout = this._onTimeout.bind(this);
    }
    watch(files, directories, startTime) {
        this.paused = false;
        var oldFileWatchers = this.fileWatchers;
        var oldDirWatchers = this.dirWatchers;
        this.fileWatchers = files.map(function(file) {
            return this._fileWatcher(file, watcherManager.watchFile(file, this.watcherOptions, startTime));
        }, this);
        this.dirWatchers = directories.map(function(dir) {
            return this._dirWatcher(dir, watcherManager.watchDirectory(dir, this.watcherOptions, startTime));
        }, this);
        oldFileWatchers.forEach(function(w) {
            w.close();
        }, this);
        oldDirWatchers.forEach(function(w) {
            w.close();
        }, this);
    };
    pause() { /**/ };
    getTimes() { /**/ };
    _fileWatcher(file, watcher) { /**/ };
    _dirWatcher(item, watcher) { /**/ };
    _onChange(item, mtime, file) { /**/ };
    _onRemove(item, file) { /**/ };
    _onTimeout() { /**/ };
    close() { /**/ };
}

module.exports = Watchpack;

function addWatchersToArray(watchers, array) { /**/ }

  本模块引入了并继承了nodejs的EventEmitter,并引入了新模块watcherManager,主要内容罗列如下:

1、构造函数接受一个对象,键包括aggregateTimeout、ignored、poll,本例只传入第一个并设置为0

2、核心方法为watch,依赖于引入的watchManager模块

3、其余方法均为工具方法

 

WatcherManager

var path = require("path");

class WatcherManager {
    constructor() {
        this.directoryWatchers = {};
    };
    // 工厂函数
    getDirectoryWatcher(directory, options) {
        // 引入模块
        var DirectoryWatcher = require("./DirectoryWatcher");
        options = options || {};
        var key = directory + " " + JSON.stringify(options);
        if (!this.directoryWatchers[key]) {
            this.directoryWatchers[key] = new DirectoryWatcher(directory, options);
            // 文件监视结束则从容器删除
            this.directoryWatchers[key].on("closed", function() {
                delete this.directoryWatchers[key];
            }.bind(this));
        }
        return this.directoryWatchers[key];
    };
    // 监视文件
    watchFile(p, options, startTime) {
        var directory = path.dirname(p);
        return this.getDirectoryWatcher(directory, options).watch(p, startTime);
    };
    // 监视目录
    watchDirectory(directory, options, startTime) {
        return this.getDirectoryWatcher(directory, options).watch(directory, startTime);
    };
}
module.exports = new WatcherManager();

  可以看出这是一个中间处理函数,其中构造函数生成了一个容器,容器的键为目录+参数生成的一个字符串,当监视关闭后会并立即删除。

  这个模块类似于tapable,是一个监视对象管理器。

 

  然后是监视核心实现模块,模块内容比较多,这里只简单看一下构造函数以及watch方法:

var EventEmitter = require("events").EventEmitter;
var async = require("async");
var chokidar = require("chokidar");
var fs = require("graceful-fs");

class Watcher {
    constructor(directoryWatcher, filePath, startTime) {
        EventEmitter.call(this);
        this.directoryWatcher = directoryWatcher;
        this.path = filePath;
        this.startTime = startTime && +startTime;
        this.data = 0;
    };
    checkStartTime(mtime, initial) { /**/ };
    close() { /**/ };
}

function DirectoryWatcher(directoryPath, options) {
    EventEmitter.call(this);
    this.options = options;
    this.path = directoryPath;
    this.files = Object.create(null);
    this.directories = Object.create(null);
    this.watcher = chokidar.watch(directoryPath, {
        ignoreInitial: true,
        persistent: true,
        followSymlinks: false,
        depth: 0,
        atomic: false,
        alwaysStat: true,
        ignorePermissionErrors: true,
        ignored: options.ignored,
        usePolling: options.poll ? true : undefined,
        interval: typeof options.poll === "number" ? options.poll : undefined,
        disableGlobbing: true
    });
    this.watcher.on("add", this.onFileAdded.bind(this));
    this.watcher.on("addDir", this.onDirectoryAdded.bind(this));
    this.watcher.on("change", this.onChange.bind(this));
    this.watcher.on("unlink", this.onFileUnlinked.bind(this));
    this.watcher.on("unlinkDir", this.onDirectoryUnlinked.bind(this));
    this.watcher.on("error", this.onWatcherError.bind(this));
    // ...
}

DirectoryWatcher.prototype.watch = function watch(filePath, startTime) {
    this.watchers[withoutCase(filePath)] = this.watchers[withoutCase(filePath)] || [];
    this.refs++;
    var watcher = new Watcher(this, filePath, startTime);
    watcher.on("closed", function() { /**/ }.bind(this));
    // ...
    return watcher;
};

// ...

module.exports = DirectoryWatcher;

  从构造函数和模块引入可以得到很多信息,如下:

1、引入了graceful-js模块,可以看出底层还是利用nodejs的fs模块来进行监视

2、所有的监视事件都是基于nodejs的EventEmitter模块来进行操作

3、内部还有一个辅助类Watcher

4、根据构造函数的代码,监视的操作包含(可能不限于)新增文件、新增文件夹、改变内容、删除文件、删除文件夹等

 

  async模块是一个类似于tapable的辅助工具,用于异步处理批量方法,详细内容可自行去网上查阅。

  构造函数中,该模块又再次引用了chokidar模块,并调用其watch方法进行初始化,看似调用方法,源码简化后如下:

class FSWatcher {
    // ...
}
exports.FSWatcher = FSWatcher;
exports.watch = function(paths, options) {
    return new FSWatcher(options).add(paths);
};

  假的,这还是个new操作,只是为了方便把两步合成到了一个方法中。

 

  所有的模块整理如上,下面几节再来剖析每一块内容。

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