Transactional Memoryfor Smalltalk

Software Composition GroupUniversity of Bern

Lukas RenggliOscar Nierstrasz

Concurrent Programmingin Smalltalk

Semaphore forMutualExclusion

RecursionLock new

Mutex new

SharedQueue new

Problems

Deadlocks

Starvation

Priority Inversion

Complexity

SoftwareTransactional Memory

Programmingwith Transactions

Lock Based

tree := BTree new.

lock := Semaphore forMutualExclusion.

" writing "

lock critical: [ tree at: #a put: 1 ].

" reading "

lock critical: [ tree at: #a ].

Transactional

tree := BTree new.

" writing "

[ tree at: #a put: 1 ] atomic.

" reading "

tree at: #a.

Inside Transactions

Our Approach

Full implementation in Smalltalk

Lazy code transformation

Method annotations

Context dependent code execution

Static Model

selector

parseTree

CompiledMethod

selector*

methods

/selector

/parseTree

AtomicMethod

atomicMethod

1

method

1

name

superclass

subclasses

instanceVariables

Class

Code Transformation

Instance Variables

Variable Bindings

Message Sends

Original Source Code

BTree>>at: aKey put: anObject

| leaf |

leaf := root leafForKey: aKey.

leaf insertKey: aKey value: anObject.

root := leaf root.

^ anObject

Transformed Source Code

BTree>>__atomic__at: aKey put: anObject

| leaf |

leaf := (self atomicInstVarAt: 1)

__atomic__leafForKey: aKey.

leaf __atomic__insertKey: aKey value: anObject.

self atomicInstVarAt: 1 put: leaf __atomic__root.

^ anObject

Transformed Source Code

BTree>>__atomic__at: aKey put: anObject

| leaf |

leaf := (self atomicInstVarAt: 1)

__atomic__leafForKey: aKey.

leaf __atomic__insertKey: aKey value: anObject.

self atomicInstVarAt: 1 put: leaf __atomic__root.

^ anObject

Transformed Source Code

BTree>>__atomic__at: aKey put: anObject

| leaf |

leaf := (self atomicInstVarAt: 1)

__atomic__leafForKey: aKey.

leaf __atomic__insertKey: aKey value: anObject.

self atomicInstVarAt: 1 put: leaf __atomic__root.

^ anObject

Annotate methodsthat need special treatment

Infrastructural code

Exception handling

Execution contexts

Many primitives

Variable sized objects

Dynamic Model

applyhasChangedhasConflict

Change

object

*changes

Process0..1

currentTransaction

do: aBlockretry: aBlockcheckpointabort: anObject

escapeContext

Transaction

previousCopyworkingCopy

ObjectChange

applyBlockconflictTestBlock

CustomChange

*

Validation

Speed Comparison

Method Invocation

Special Method Invocation

Instance Variable Read

Instance Variable Write

Indexed Variable Read

Indexed Variable Write

5× 10×

15×

20×

25×

17×

18×

19×

20×

2×

1×

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

800.0

0 10 20 30 40 50 60 70 80 90 100

non-synchronized lock-based transactional

n

t [ms]

Performance of n concurrent edit operations in Pier

1 CPU

2 CPUs

4 CPUs

8 CPUs

Future Work

Implement within a multi-core environment

Improve speed

Applications

Concurrency Contol

Source Code Loading

Context Oriented Programming