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Lecture 18: Method Inlining

Computer Science 313 – Advanced Programming Topics. Lecture 18: Method Inlining. Handling Common Subroutines. Must perform set of actions in many places. Handling Common Subroutines. Must perform set of actions in many places. Paste code into each different method.

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Lecture 18: Method Inlining

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  1. Computer Science 313 – Advanced Programming Topics Lecture 18:Method Inlining

  2. Handling Common Subroutines • Must perform set of actions in many places

  3. Handling Common Subroutines • Must perform set of actions in many places • Paste code into each different method • Write 1 method called everywhere

  4. Why Write a Separate Method • Fewer errors from not updating 1 copy • Code is much simpler to debug • Optimizing & refactoring code far simpler • Makes code more reusable

  5. Why Copy-and-Paste Code • Calls expensive relative to most code • Calls will take 10-12 instructions each • Violates assumption of next instruction executed • Compiler may be prevented from optimizing • Unadulterated stupidity making these comments • In many situations,costs do not matter • Only on critical path should we even think about this • Remember Amdahl’s law:10% slowdown to 20% of code = 0.97 slowdown

  6. Method Inlining • From Michael Hind, a leading IBM researcher • Best solution looks like copy-and-paste code • Easiest way to tell if someone a poseur

  7. What is Inlining? • Replaces method call with actual code • Acts as if written using copy-and-paste • But does not suck when maintaining code public int add(int a, int b) {if (b == 3) { return add3(a); }return a + b; } public int add3(int x) {return x + 3; }

  8. What is Inlining? • Replaces method call with actual code • Acts as if written using copy-and-paste • But does not suck when maintaining code public int add(int a, int b) {if (b == 3) { return add3(a); }return a + b; } public int add3(int x) {return x + 3; }

  9. What is Inlining? • Replaces method call with actual code • Acts as if written using copy-and-paste • But does not suck when maintaining code public int add(int a, int b) {if (b == 3) { return a + 3; }return a + b; } public int add3(int x) {return x + 3; }

  10. C/C++ Inlining Options • Suggest to compiler with inline keyword • Allows programmer to hint at function to inline • Compiler may override if not a good idea inline int add3(int x) { return x + 3; } • Rewrite function as macro using #define • Global search-and-replace performed on code • Compiler has no choice; function forced inline • Create absolute nightmare for maintenance

  11. Inlining Support in Java • Automatically inlines certain smallmethods • But only if and when exact definition known • Subclasses cannot change definition later • Method must be static, final, or private • Code must be written to use this skill • Rare for people to know details of this • Simple poseur detector from not knowing this

  12. Inlining Support in Java • Automatically inlines certain smallmethods • But only if and when exact definition known • Subclasses cannot change definition later • Method must be static, final, or private • Code must be written to use this skill • Rare for people to know details of this • Simple poseur detector from not knowing this How not to look like an idiot:

  13. Do the Right (Coding) Thing • Breakup code & write only small methods • Small ones privatefinal to get inlined • Methods far easier to write, debug, & reuse • All benefits and no slowdown!

  14. CSC212/213 Professor Fun! • Make methods static when possible • Code becomes easier to read and follow • Ensures everything can be inlined • Make fields private & use get methods • Make accessorfinalsince it cannot be changed • Guess what, the getter code gets inlined

  15. Bad Methods; No Inline public int three() { return 3; }public int two() { return 2; }public int five() { return three() + two(); }public intaddToX(int y) { return x + y; }public intgetAndUpdateX(int z) { x = x + z; return x;}

  16. Now We Can Inline public staticint three() { return 3; }public staticinttwo() { return 2; }public staticintfive() {return three()+two();}privateintaddToX(int y) { return x + y; }public final intgetAndUpdateX(int z) { x = addToX(z); return x;}

  17. Simple Java Inlining Results

  18. JIT Advantage • So far,inlining based on static analysis • Information available when program compiled • Only inlines small methods, since they are safe • But calling larger methods also takes time • Java has JITcompiler it can use • Information gathered as program runs • Frequent calls (hot paths) will be found

  19. Next Step To Worry About • Can inlinemethods on critical path • Even when larger than otherwise allowed • Even if not final, if calls are not polymorphic • JVM does this automatically • So may not hurt to use patterns on critical path!

  20. Inlining Even When We Cannot

  21. For Next Class • Lab #5 on Angel & due week from Fri. • Read pages 191 - 202 in book • Command pattern will be focus of reading • Great for when we need to use remote control • How do we use Command pattern? • How does it fit in with other patterns? • Where should this be used? • Is the pattern behavioral, creational, or structural?

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