WebKit Child Resource Loading process

A Web page consists of a main document and a child resource. The main document describes the Web page's frame, layout. Child resources are the child elements that make up a webpage, including pictures,CSS,JS , and so on. In order to display a Web page, you first load the resource into memory. Loading refers to the process of loading the required resources into memory. Webkit uses a lot of caching mechanisms, which may be loaded from the network or from the local cache. The load of Webkit is divided into two lines, one is the loading of the main document, and the other is the loading of the child resources.

You first need to parse the main document before you know which child resources to use. However, it is not important to wait until the main document is parsed to load the child resources, or the edge-resolved edge-loaded sub-resources, that is, the partial main document begins to parse, parsing to a child resource begins to load.

The following is an example of the process of loading a child resource by loading a picture resource.

When parsing the main document, it is necessary to find aImageresource, and then notifyImageloaderLoadingImageResources. ImageloaderNoticeCachedresourceloadersends a load request. LoaderFirst QueryMemoryCacheIf there is a resource, none creates aCachedimagerepresents the resource. Then throughResourceloaderschedulerdispatches a load request. ResourceloaderschedulerCreate aSubresourceloaderinstance to complete the load request (create->init->sendrequest). Resourcehandleresponsible for interacting with platform-related interfaces, sending requests and platform-related layers, retrieving data from the platform-related layer. In theAndroidplatform, the load request passes through theResourcehandlepassed toWebkit, inWebkitlayers also involve many classes. First queryhttpif the cache has this resource, no network requests are sent. After the data is returned, it is passed through various callbacks toWebCorethe.

complete the loading of a resource, involving dozens of classes. is quite complicated.