Announcements & Review

Read Ch GU1 & GU2 Cohoon & Davidson Ch 14 Reges & Stepp Lab 10 set game due 4/26 Exam 2 Wed 5/2 5:30-7:30 GEO 2.216 Last few times: GUI Today: Research in Programming Languages introduction to memory management Announcements & Review Lecture 36: Programming Languages & Memory Management

Software Developer Dreams Lecture 36: Programming Languages & Memory Management

Software Developer Dreams • Easy to implement specifications • Easy to get correct • Robust to errors of all sorts • Easy to maintain • Runs fast Lecture 36: Programming Languages & Memory Management

Impediments to the Dream • Applications growing bigger & more complex • Application knowledge spread thin • Testing is not enough • Architectures growing more complex • Single core complexity • Multicore • The glue is more complicated • Dynamic optimization & runtime systems • Coordination between multiple languages and runtime systems • Impossible to test all scenarios Difficult to understand the program or its runtime behavior Lecture 36: Programming Languages & Memory Management

Multi-pronged Approach to Correct High Performance Software • Better languages • Java and C# are not the last programming languages • Validation when possible • We probably will not be able to validate substantial parallel applications any time soon • Is application growth outpacing validation advances? • Analysis and development tools • Static bug finding tools • Dynamic optimization • Dynamic bug finding tools • Self healing systems • Don’t crash • Dynamically updatable systems • Evaluation Performance still matters unobtrusive, low overhead approaches Lecture 36: Programming Languages & Memory Management

Java put garbage collection into widespread use • In Java • programs use “new” • objects abstract their location, i.e., a program never records an object address • Therefore, objects can move • programs contain no “free/delete” • easier to program, since you don’t have to figure out when an object becomes unreachable • In C and C++ • programmers use “new” and “free/delete” • programs can record the address of an object in variables which causes errors, e.g., buffer overflow • Therefore, objects may not move Lecture 36: Programming Languages & Memory Management

Example • Program with classes for plates, bowls, & silverware • What happens in memory when the program says new? Lecture 36: Programming Languages & Memory Management

Select Plates, Bowls, Silverware Objects Lecture 36: Programming Languages & Memory Management

Select Plates, Bowls, Silverware Lecture 36: Programming Languages & Memory Management

Explicit Memory Management:Hand Wash Dishes Lecture 36: Programming Languages & Memory Management

Dish Washer: Automatic Memory ManagementGarbage Collection • Dad is the garbage collector • Do forever • Prepare meal • Select plates, bowls, silverware • Serve food & Eat • Dad put dishes in dishwasher • Dad checks if dishwasher full or • Out of plates, bowls or silverware • Dadruns dishwasher Lecture 36: Programming Languages & Memory Management

Select Plates, Bowls, Silverware Lecture 36: Programming Languages & Memory Management

Dad Runs Dish Washer & Puts Up Dishes Lecture 36: Programming Languages & Memory Management

Memory System Organization Registers Instruction Cache CPU Central Processing Unit Level 2 Cache Data Cache Memory Lecture 36: Programming Languages & Memory Management

Mapping Dishes to Computer Resources chunks of memory Class Declarations Lecture 36: Programming Languages & Memory Management

Contiguous Allocation Plate p = new Plate(); Lecture 36: Programming Languages & Memory Management

Contiguous Allocation Plate p1 = new Plate(); Plate p2 = new Plate(); Bowl b1 = new Bowl(); Fork f1 = new Fork(); Fork f2 = new Fork(); Spoon s1 = new Spoon(); Lecture 36: Programming Languages & Memory Management

Contiguous Allocation etc. Lecture 36: Programming Languages & Memory Management

Explicit Memory ManagementFree with Continuous Allocation Free (b3) Lecture 36: Programming Languages & Memory Management

Free with Contiguous Allocation Free (b3) Free (s1) Lecture 36: Programming Languages & Memory Management

Garbage Collectionwith Contiguous Allocation Wait longer Lecture 36: Programming Languages & Memory Management

Garbage Collection with Contiguous Allocation L L Find live objects: L L L Lecture 36: Programming Languages & Memory Management

Garbage Collection with Contiguous Allocation Find live objects: L Copy live objects to new area L Lecture 36: Programming Languages & Memory Management

Garbage Collection with Contiguous Allocation Find live objects: L Copy live objects to new area Reclaim old space L Lecture 36: Programming Languages & Memory Management

Garbage Collection with Contiguous Allocation Find live objects: L Copy them to new area Reclaim old space Allocate into new space Lecture 36: Programming Languages & Memory Management

Allocation withSize-Class Free-Lists Lecture 36: Programming Languages & Memory Management

Allocation withSize-Class Free-Lists Free (b3) Free (s1) Lecture 36: Programming Languages & Memory Management

Allocation withSize-Class Free-Lists free list size 24 bytes free list size 20 bytes ... We can use linked lists for each list of free sizes to find the free ones ... Lecture 36: Programming Languages & Memory Management

Memory Management • All memory management uses one of these two basic mechanisms • Contiguous allocation • Size-Class Free-Lists • Classic Computer Science Problem in Space-Time tradeoff Lecture 36: Programming Languages & Memory Management

Other Key Ideas in Memory Management • Locality • Incrementality • Generational behavior • Older-first behavior • My research group introduced this one! Lecture 36: Programming Languages & Memory Management

Announcements & Review