Re:Open-sourcing Chrome on iOS
by DonHopkins on Tuesday January 31, 2017 @02:28PM
(#13534298)
It's my understanding that only embedded WKWebViews are allowed to enable the JIT compiler, but not UIWebViews (or in-process JavaScriptCore engines). WKWebView is an out-of-process web browser that uses IOSurface [1] to project the image into your embedding application and IPC to send messages.
So WKWebView's dynamically generated code is running safely firewalled in a separate address space controlled by Apple and not accessible to your app, while older UIWebViews run in the address space of your application, and aren't allowed to write to code pages, so their JIT compiler is disabled.
Since it's running in another process, WkWebView's JavaScriptEngine lacks the ability to expose your own Objective C classes to JavaScript so they can be called directly [2], but it does include a less efficient way of adding script message handlers that call back to Objective C code via IPC [3].
So WKWebView's dynamically generated code is running safely firewalled in a separate address space controlled by Apple and not accessible to your app, while older UIWebViews run in the address space of your application, and aren't allowed to write to code pages, so their JIT compiler is disabled.
Since it's running in another process, WkWebView's JavaScriptEngine lacks the ability to expose your own Objective C classes to JavaScript so they can be called directly [2], but it does include a less efficient way of adding script message handlers that call back to Objective C code via IPC [3].
[1] https://developer.apple.com/reference/iosurface
[2] https://developer.apple.com/reference/javascriptcore/jsexpor...
[3] https://developer.apple.com/reference/webkit/wkusercontentco...