Export to GitHub

nitrox - Performance.wiki

Introduction

Add your content here.

Details

The three different methods for calling into Objective-C from Javascript have some significant performance implications.

Underlying Mechanisms

Native Obj-C bridge:

  • Uses standard WebKit methods which are not yet documented/exposed in the iPhone 2.1 OS SDK
  • Relies upon the native WebKit Objective-C / Javascript bridging capabilities
  • (Presumably) allows reference counting between language domains, which is a huge win
  • Can translate simple data types (NSString, NSNumber) and wraps others in WebScriptObject
  • Allows synchronous and asynchronous operation

UIWebView URL loading hook:

  • Relies only upon documented and iPhone-kosher UIWebView delegate and UIWebView methods
  • Semantics of setting window.location are unclear, but no return value comes from a set of window.location
  • Only allows data types which can be expressed as JSON (or other string form)
  • Allows only asynchronous operation.

XMLHTTPRequest / Ajax:

  • Relies upon documented and iPhone-kosher networking APIs
  • Has a relatively large code footprint due to embedded HTTP server
  • High latency, but better handling of large or binary data sets
  • Only allows data types which can be expressed as JSON (or other string form)
  • Could theoretically be used for distributed RPC between iPhones
  • Allows both synchronous and asynchronous operation

Benchmarking Invocation Methods

All tests were performed with NSLog nullified to reduce overhead.

There's a much steeper performance curve on the Simulator than on actual hardware. However, it looks like at least a 4-5x overhead increase from the fastest method to the Ajax / XMLHTTPRequest method used by Nitrox.

Performance on first-gen iPhone Hardware, OS 2.1

| Method | Time | |:-------|:-----| | native Obj-C bridge | 10.26 ms | | URL loading hook | 16.92 ms | | XMLHTTPRequest / Ajax | 65.18 ms |

Performance on Macbook Pro, Simulator, OS 2.1

| Method | Time | |:-------|:-----| | native Obj-C bridge | 0.04 ms | | URL loading hook | 0.54 ms | | XMLHTTPRequest / Ajax | 2.16 ms |