Announcements

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Announcements Review

• Last few times
• GUI
• Today
• Research in Programming Languages
• introduction to memory management

• Read
• Ch GU1 GU2 Cohoon Davidson
• Ch 14 Reges Stepp
• Lab 10 set game
• due 4/26
• Exam 2
• Wed 5/2 530-730
• GEO 2.216

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Software Developer Dreams
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Software Developer Dreams

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

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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

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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
• Dont crash
• Dynamically updatable systems
• Evaluation
• Performance still matters
• unobtrusive, low overhead approaches

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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 dont 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

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Example

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

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Select Plates, Bowls, Silverware Objects
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Select Plates, Bowls, Silverware
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Explicit Memory ManagementHand Wash Dishes
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Explicit Memory ManagementHand Wash Dishes
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Explicit Memory ManagementHand Wash Dishes
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Explicit Memory ManagementHand Wash Dishes
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Explicit Memory ManagementHand Wash Dishes
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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
• Dad runs dishwasher

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Select Plates, Bowls, Silverware
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Select Plates, Bowls, Silverware
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Dad Runs Dish Washer Puts Up Dishes
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Memory System Organization
Registers
Instruction Cache
CPU Central Processing Unit
Level 2 Cache
Data Cache
Memory
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Mapping Dishes to Computer Resources
chunks of memory
Class Declarations
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Contiguous Allocation
Plate p new Plate()
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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()
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Contiguous Allocation
etc.
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Explicit Memory ManagementFree with Continuous
Allocation
Free (b3)
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Free with Contiguous Allocation
Free (b3) Free (s1)
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Garbage Collectionwith Contiguous Allocation
Wait longer
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Garbage Collection with Contiguous Allocation
L
L
Find live objects L
L
L
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Garbage Collection with Contiguous Allocation
Find live objects L Copy live objects to new area
L
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Garbage Collection with Contiguous Allocation
Find live objects L Copy live objects to new
area Reclaim old space
L
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Garbage Collection with Contiguous Allocation
Find live objects L Copy them to new
area Reclaim old space Allocate into new space
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Allocation withSize-Class Free-Lists
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Allocation withSize-Class Free-Lists
Free (b3) Free (s1)
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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
...
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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

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Other Key Ideas in Memory Management

• Locality
• Incrementality
• Generational behavior
• Older-first behavior
• My research group introduced this one!