Embed Size (px)
DESCRIPTION
Software Transactional Memory for Dynamic-Sized Data Structures. Maurice Herlihy, Victor Luchangco, Mark Moir, William Scherer Presented by: Gokul Soundararajan. Outline. Background Software Transactional Memory (STM) Implementation Long Example Experimental Results Conclusion. - PowerPoint PPT Presentation
Citation preview
Software Transactional Software Transactional Memory for Dynamic-Memory for Dynamic-Sized Data StructuresSized Data Structures
Maurice Herlihy, Victor Luchangco, Mark Maurice Herlihy, Victor Luchangco, Mark Moir, William SchererMoir, William Scherer
Presented by: Gokul SoundararajanPresented by: Gokul Soundararajan
22
OutlineOutline
BackgroundBackground Software Transactional Memory Software Transactional Memory
(STM)(STM)– ImplementationImplementation– Long ExampleLong Example
Experimental ResultsExperimental Results ConclusionConclusion
33
TransactionTransaction
A sequence of operations on components of a data structure executed by a single thread
AtomicAtomic: either– Commits: takes effect– Aborts: its effects are discarded
Linearizable: preserves program order
44
Transactional MemoryTransactional Memory
Any system that supports concurrent execution of transactions performed by threads
Originally, a hardware idea Now, implemented in software
55
Transactional ObjectsTransactional Objects
Is a containercontainer for a regular object A transaction accesses it
– Open – Read/modify– Changes are not seen until the transaction
commits Creation and initialization of a
transactional object is not a part of any transaction
66
DSTM ImplementationDSTM Implementation
Is a containercontainer for a regular object
TMObject classTMObject class– Implements a Implements a
transactional objecttransactional object
Class: TMObject
Locator {Transaction, oldObject, newObject}Locator * startopen( )release( )
77
DSTM ImplementationDSTM Implementation
transaction
oldObject
newObject
The transactionthat most recently opened the object
in WRITE mode
A new object version
An old objectversion
start
TMObject
Locator
88
Current VersionCurrent Version
Current version of a transactional objectCurrent version of a transactional object– Determined by the status of the transaction Determined by the status of the transaction
(T) that most recently opened the object in (T) that most recently opened the object in WRITE modeWRITE modeT StatusT Status Current Current
VersionVersionOther Other
VersionVersion
COMMITTEDCOMMITTED newObjectnewObject meaninglessmeaningless
ABORTEDABORTED oldObjectoldObject meaninglessmeaningless
ACTIVEACTIVE oldObjectoldObject TentativeTentativeVersionVersion
99
Open(WRITE): T is COMMITTEDOpen(WRITE): T is COMMITTED
transaction
oldObjectnewObject
T: COMMITTED
newVersion
oldVersionstart
myObj
1010
Open(WRITE): T is COMMITTEDOpen(WRITE): T is COMMITTED
transaction
oldObjectnewObject
T: COMMITTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
A opens myObjin WRITE mode
myObj
1111
Open(WRITE): T is COMMITTEDOpen(WRITE): T is COMMITTED
transaction
oldObjectnewObject
T: COMMITTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofnewVersion
A opens myObjin WRITE mode
myObj
copy
1212
Open(WRITE): T is COMMITTEDOpen(WRITE): T is COMMITTED
transaction
oldObjectnewObject
T: COMMITTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofnewVersion
A opens myObjin WRITE mode
myObj
copy
1313
Open(WRITE): T is COMMITTEDOpen(WRITE): T is COMMITTED
transaction
oldObjectnewObject
T: COMMITTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofnewVersion
A opens myObjin WRITE mode
myObj
copy
CAS
1414
Open(WRITE): T is ABORTEDOpen(WRITE): T is ABORTED
transaction
oldObjectnewObject
T: ABORTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
A opens myObjin WRITE mode
myObj
1515
Open(WRITE): T is ABORTEDOpen(WRITE): T is ABORTED
transaction
oldObjectnewObject
T: ABORTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofoldVersion
A opens myObjin WRITE mode
myObj
copy
1616
Open(WRITE): T is ABORTEDOpen(WRITE): T is ABORTED
transaction
oldObjectnewObject
T: ABORTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofoldVersion
A opens myObjin WRITE mode
myObj
copy
1717
Open(WRITE): T is ABORTEDOpen(WRITE): T is ABORTED
transaction
oldObjectnewObject
T: ABORTED
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
Copy ofoldVersion
A opens myObjin WRITE mode
myObj
copy
1818
Open(WRITE): T is ACTIVEOpen(WRITE): T is ACTIVE
transaction
oldObjectnewObject
T: ACTIVE
newVersion
oldVersionstart
transaction
oldObjectnewObject
A: ACTIVE
A opens myObjin WRITE mode
myObj
A tries to abort T
?
1919
Example: Integer SetExample: Integer Set
Specifications:Specifications:– Object: Integer SetObject: Integer Set– Supports:Supports:
insert(v)insert(v) delete(v)delete(v) member(v)member(v)
Implementation:Implementation:– Linked list of a set of elementsLinked list of a set of elements– Sorted in ascending orderSorted in ascending order
2020
Integer Set Example:Integer Set Example:ConstructorConstructor
MINnext
MAXnext
start start
2121
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
first
thread
40next
newElm
TACTIVE
start startstartstart
TCOMMITEDstart
newNode
2222
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
40next
newElm
TACTIVE
start startstartstart
TNO
TCOMMITEDstart
newNode
2323
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
-20next
40next
newElm
TACTIVE
start startstartstart
TNO
TNO
TCOMMITEDstart
newNode
2424
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
-20next
40next
newElm
30next
TACTIVE
start startstartstart
TNO
TNO
TNO
TCOMMITEDstart
newNode
2525
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
-20next
40next
newElm
30next
TACTIVE
start startstartstart
TNO
TNO
TNO
TCOMMITEDstart
newNode
2626
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
-20next
40next
newElm
30next
MAXnext
TACTIVE
start startstartstart
TNO
TNO
TNO
TNO
TCOMMITEDstart
newNode
2727
Integer Set Example: Integer Set Example: insert(40)insert(40)
MINnext
MAXnext
-20next
30next
MINnext
first
thread
-20next
40next
newElm
30next
MAXnext
TACTIVE
start startstartstart
TNO
TNO
TNO
TNO
TCOMMITEDstart
newNode
2828
DSTM and Sequential CodeDSTM and Sequential Code
Differences:Differences:– Need to catch Denied exceptionNeed to catch Denied exception– Retry transaction that fails to commitRetry transaction that fails to commit– Distinguish between transactional Distinguish between transactional
objects and non-transactional objectsobjects and non-transactional objects
2929
Obstruction FreedomObstruction Freedom Guarantees progress for any thread that Guarantees progress for any thread that
eventually executes without interference eventually executes without interference for a sufficient number of stepsfor a sufficient number of steps
Strong enough to avoid problems Strong enough to avoid problems associated with locksassociated with locks
Ensures that no thread can be blocked by Ensures that no thread can be blocked by delays or failures of other threadsdelays or failures of other threads
Live-lockLive-lock– Livelock Freedom - If some process wants to Livelock Freedom - If some process wants to
enter the critical section, then some process enter the critical section, then some process will eventually enter the critical section.will eventually enter the critical section.
3030
Obstruction FreedomObstruction Freedom Weaker progress guarantee than wait-Weaker progress guarantee than wait-
freedom freedom – All processes are guaranteed to complete the All processes are guaranteed to complete the
access in finite time, regardless of the actions access in finite time, regardless of the actions of the other processes.of the other processes.
BUT:BUT:Efficient
Contention
Manager+
Obstruction
Freedom
Wait
Freedom
In Practice
3131
Contention ManagementContention Management
Methods:Methods:– AggressiveAggressive
Abort the conflicting transactionAbort the conflicting transaction Interrupting a partially executed Interrupting a partially executed
operation will not jeopardise correctnessoperation will not jeopardise correctness
– PolitePolite Operations “back off” when they Operations “back off” when they
encounter interferenceencounter interference Wait for some time before retryingWait for some time before retrying
3232
Contention ManagementContention Management
Contention manager is invoked only Contention manager is invoked only in case of contention in case of contention
In most lock-free and wait-free In most lock-free and wait-free implementations, mechanisms used implementations, mechanisms used to ensure progress impose significant to ensure progress impose significant overhead even in the absence of overhead even in the absence of contentioncontention
3333
ExperimentsExperiments
BenchmarksBenchmarks– IntSetIntSet– IntSet with Early ReleaseIntSet with Early Release– RBTreeRBTree
Contention ManagementContention Management– AggressiveAggressive – abort the conflicting – abort the conflicting
transactiontransaction– PolitePolite – have a back-off algorithm – have a back-off algorithm
3434
ResultsResults
3535
ResultsResults
3636
ResultsResults
3737
ResultsResults
3838
ConclusionConclusion
PresentedPresented– Transactional Memory in Java/C++Transactional Memory in Java/C++– Probably easier in Java (because of the Probably easier in Java (because of the
Object data type)Object data type)– Good performance over simple lockingGood performance over simple locking
