ARChon 分析之七：启动流程分析

引文
通过前面几篇文章的介绍，现在来看ARChon的js代码就简单多了。基础代码是 ARC 的运行环境。然后ChromeApp启动，ChromeApp在配置项中配置了apk的路径。然后调用 ARChon的扩展程序。打开一个窗口。

那么 ARChon 从哪里看起呢？

main.js

chrome.app.runtime.onLaunched.addListener(onLaunch);

...

launchAppWindow();

...

function launchAppWindow(opt_userEmail) {
    var time_0 = (new Date()).getTime();
    var abs_index_html = 'runtime/gen_index.min.html';
    var window_id = '';
    var runtime_id = getRuntimeID();
    // Workaround crbug.com/180039 by constructing the absolute path (within
    // the App CRX root) to index.html
    abs_index_html = '/_modules/' + runtime_id + '/gen_index.min.html';
    window_id = runtime_id;

    // Override the window ID so App windows from tests will be distinct.
    if (args.hasOwnProperty('windowIdOverride')) {
      window_id = args['windowIdOverride'];
    }

    appWindow = chrome.app.window.get(window_id);
    if (appWindow != null && !args.forceWindowCreate) {
      var onRelaunched = appWindow.contentWindow.arc.onRelaunched;
      if (!onRelaunched) {
        console.error('onLaunched is called during initialization.');
        return;
      }
      onRelaunched(args);
      return;
    }

    // Note: The code above this point runs every time the App Launcher
    // icon is clicked, regardless of whether the App is currently launched.
    // Do not put one-time init code above this point.
    // TODO(crbug.com/417403): Refactor this whole function, there are clearly
    // two paths here, one for when the app is already launched and needs to
    // be relaunched, and when we need a new window to be created.  There
    // should not be the need for a comment like this about not putting one-time
    // init code in "launchAppWindow".

    console.time('ARC Window Popup');
    maybeKillDexopt_();
    crashReporter.init();
    var appWidth = arcMetadata.getValue('width');
    var appHeight = arcMetadata.getValue('height') + _TOPBAR_HEIGHT;

    var options = {
      // Specify an id for the window to make the window a singleton.
      id: window_id,
      // TODO(jhorwich) Switch to innerBounds when Chrome 36 is stable as this
      // bounds is deprecated in favor of innerBounds.
      width: appWidth,
      height: appHeight,
      resizable: arcMetadata.getValue('resize') != 'disabled',
      // Showing the app window is not a cheap operation for the browser
      // process. Not to slow down nexe loading, create the window with
      // 'hidden: true', and show it later in plugin.js when the process
      // is idle.
      hidden: true,
      frame: 'none'
    };

    if (!systemDirectoriesCreated) {
      systemDirectoriesCreated = createSystemDirectories();
    }

    chrome.app.window.create(abs_index_html, options, function(w) {
      console.timeEnd('ARC Window Popup');
      console.time('ARC appWindow Init');
      if (opt_appWindowCreationCallback)
        opt_appWindowCreationCallback(w);

      appWindow = w;
      appWindow.contentWindow['arc'] = {
        launchArgs: args,
        appLaunchTime: time_0,
        backgroundPage: window,
        runtimeUpdatedWhileRunning: null,
        userEmail: opt_userEmail,
        systemDirectoriesReady: new PromiseBridge(systemDirectoriesCreated)
      };

      appWindow.setBounds({width: appWidth, height: appHeight});
      appWindow.contentWindow.openParentWindow = function(url) {
        return window.open(url);
      };
      appWindow.onClosed.addListener(function() {
        appWindow = null;
        // Reset |appLaunched| so that the onInstalled handler can dexopt
        // an apk when the app is auto-updated.
        appLaunched = false;
      });
      console.timeEnd('ARC appWindow Init');
    });
}

可以看到，它是获取了ARC运行环境，然后把参数（arcMetadata）都填给ARC。dexopt等安装细节、窗口的显示与渲染、点击事件的输出都是ARC处理的。通过nmf的配置文件可知，chrome会先做连接，然后启动 arc_nacl_x86_64.nexe 。

那么什么是ARC？如何编译呢？参考这篇文章的背景介绍。

// TODO 未完待续

ARChon 分析之七：启动流程分析

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