Designing and Shipping a Platform – Joshua Goodman

• Common Language Runtime, Group Program manager

• Why & How?
  • Platforms give your users far more features and flexibility
  • Platforms create ecosystems
    • Windows
    • iPhone
      • Windows 7 mobile will be better platform but there will be way less apps than iPhone
• Strategy – Build your app on your platform
  • Forces you to be extensible enough – great architecture
  • High test burden
  • Are pieces of your app completely replaceable?
    • More extensible
    • Extensions can interfere
    • Upgrades more likely to break things
• Browsers: Three Strategies
  • Firefox
    • Build platform, then build application on top
  • IE
    • Well defined addin model for toolbars
  • Safari
• Why high compatibility is so hard
  • .Net 1.1 is compatible with 1.0
  • Install 1.1 and Outlook will crash, not their code but customers do not care
• Layer cake approach
  • .Net 2.0, 3.0, 3.5 on top of each other
• Side by side approach
  • Old stuff uses old thing, new stuff uses new thing
  • .Net 4.0 is different from 2.0, 3.0, & 3.5.  It is on the side
  • Use shim layer
  • Window 7, runs XP in virtual machine
  • Apple uses emulator of old OS
  • Flash Player 9
    • Two virtual machines, AVM1 & AVM2
  • Still hard
    • They still have to compatible or developers will not use new platform
    • Side by side libraries, how about all the libraries you bought for the older version?
• App-Compat Flags
  • App tells what version it wants
  • Need to write code for old and new platforms
  • What about libraries?
• In process side-by-side for .Net 4.0
  • You can run both 4.0 and 2.0 in the process
• Frozen Designs
  • Once you build it, you are stuck
    • Hard to remove APIs
    • Hard to change behavior
    • Get it right first time or live with your mistakes
  • For an app, much easier
    • You can look for a the hooks in an app, not so with a platform
• Best Practices:
  • Mocks: Mock a deployment and test all
  • Compatibility
    • Team must get to same page on compatibility bar
      • Document and communicate
    • Compat council makes decision
• Use your Apps
  • Keep 300 applications running
  • Test against them – find breaking changes
  • Analyze the IL to see how often functions are called
  • Use source code of apps that build on top when available
• Design Process
  • Understand root of partner problem
    • Try to solve it without changes
    • Partners jump to a solution but not the best solution
  • Politely request data
• Hard Problem: Obsoleting
  • Removing it breaks partners
  • Mark as “obsolete”
  • Discourage use
  • Hope some day people will stop using it
• Platform Growth
  • It will keep growing
  • Moving towards more layered approach
  • Hard to shrink
• Conclusion
  • Get it right the first time
  • Architect for compatibility
• My thoughts: We don’t build platforms, but we can learn form them as we add modules with the Archie Team.