announcements & review

Lecture 36: Programming Languages & Memory Management

Announcements & Review

Read Ch GU1 & GU2 Cohoon & DavidsonCh 14 Reges & Stepp

Lab 10 set gamedue 4/26

Exam 2 Wed 5/2 5:30-7:30GEO 2.216

Last few times:GUI

Today: Research in Programming Languagesintroduction to memory management


Software Developer Dreams


Software Developer Dreams

• Easy to implement specifications• Easy to get correct• Robust to errors of all sorts• Easy to maintain• Runs fast


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


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 mattersunobtrusive, low overhead approaches


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


Example• Program with classes for plates, bowls, & silverware• What happens in memory when the program says new?


Select Plates, Bowls, Silverware Objects


Select Plates, Bowls, Silverware


Explicit Memory Management:

Hand Wash Dishes


Dish Washer: Automatic Memory Management

Garbage 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

– Dad runs dishwasher


Select Plates, Bowls, Silverware


Dad Runs Dish Washer

& Puts Up Dishes


Memory System Organization

Registers

CPUCentral

Processing Unit

InstructionCache

DataCache

Level 2Cache

Memory


Mapping Dishes to Computer

Resources

Class Declarations

chunks of memory


Contiguous Allocation

Plate p = new Plate();



Plate p1 = new Plate(); Plate p2 = new Plate(); Bowl b1 = new Bowl(); Fork f1 = new Fork(); Fork f2 = new Fork();Spoon s1 = new Spoon();



etc.


Explicit Memory Management

Free with Continuous Allocation

Free (b3)


Free with Contiguous Allocation

Free (b3)Free (s1)


Garbage Collectionwith Contiguous Allocation

Wait longer


Garbage Collection with Contiguous

Allocation

Find live objects: L

L L

L L


Find live objects: LCopy live objects to new area

L


Allocation


Find live objects: LCopy live objects to new areaReclaim old space

L


Allocation


Find live objects: LCopy them to new areaReclaim old spaceAllocate into new space


Allocation


Allocation withSize-Class Free-Lists


Free (b3)Free (s1)



We can use linked listsfor each list of free sizesto find the free ones


...

...

free list size 24 bytes

free list size 20 bytes


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


Other Key Ideas in Memory Management

• Locality• Incrementality• Generational behavior• Older-first behavior

– My research group introduced this one!

announcements & review

Documents

new plate plate p2

new fork fork f2

explicit memory managementfree

dishwasherselect plates

silverwareselect plates

new plate bowl b1

new bowl fork f1

new forkspoon s1