1.
Practical Solutions
for Multicore Programming
Dr. Guy Korland

2.
Process 1
a = acc.get()
a = a + 100
Process 2
b = acc.get()
b = b + 50
acc.set(b)
acc.set(a)
... Lost Update! ...

3.
Process 1
Process 2
lock(A)
lock(B)
….
lock(A)
lock(A)
... DeadLock! ...

4.
Process 1
Process 2
atomic{
a = acc.get()
a = a + 100
acc.set(a)
}
atomic{
b = acc.get()
b = b + 50
acc.set(b)
}
... WIIIII! ...

5.
Intel TSX
if(_xbegin()==-1) {
if( !fallback_mutex.is_acquired() ) {
tions.
sums[mygroup] += data[i];e instruc
impl
} else {
d to s
e
_xabort(1);
● Limit
ll-back
fa
}
erency
Coh
uires
● _xend();
Req
Cache
} else {
ing on
●fallback_mutex.acquire();
Relay
sums[mygroup] += data[i];
fallback_mutex.release();
}

6.
We still need
Software Transactional Memory

7.
DSTM2
Maurice Herlihy et al, A flexible framework … [OOPSLA06]
@atomic public interface INode{
int getValue ();
void setValue (int value );
jects.
}
to Ob
d
imite
L
sive.
Factory<INode> factory ru
int = Thread.makeFactory(INode.class );
aries.
●
final INodeVery factory.create(); ort libr
node =
factory result = Thread.doIt(new Callable<Boolean>() {
’t supp e (fork).
n
● Does
public Boolean call nc
rma () {
return node.setValue(value);
perfo
● Bad
} });
●

8.
JVSTM
João Cachopo and António Rito-Silva, Versioned boxes as the
basis for memory transactions [SCOOL05]
public class Account{
private VBox<Long> balance = new aries.
VBox<Long>();
}
rt libr
suppo
public @Atomic void withdraw(long amount) {
esn’t
● Do
e. - amount); hared fields
balance.put rusiv
int(balance.get() nce” s
● Less
}
nnou
to “A
● Need

9.
Atom-Java
B. Hindman and D. Grossman. Atomicity via source-tosource
translation. [MSPC06]
public void update ( double value) {
Atomic {
ord.
w
commission += value; erved
a res
tion.
● Add
}
ompila ries.
pre-c
}
ibra
●
eed
N
ort l
’t supp sive.
n
● Does
s intru
n Les
● Eve

10.
Deuce STM - API
G. Korland, N. Shavit and P. Felber, “Noninvasive Java
Concurrency with Deuce STM”, [MultiProg '10]
public class Bank{
rds.
ed wo
private double commission = 10;
serv
No re
ased.
nb
tion.
@Atomicnnotatio
mpila
● A
re co
pac1,-Account ac2,rdouble amount){
public void transaction( Account
ies.
d for
ee
● No n (amount + commission);lib
al ra ol
ac1.balance -=
xtern
ac2.balanceppamount;e
+= orts
rch to
● Su
resea
}
able –
d
● Exten
}
●

11.
Deuce STM - Overview

12.
Benchmarks
(Sun UltraSPARC T2 Plus – 2 x Quad x 8 HT)

13.
Benchmarks
(Azul – Vega2 – 2 x 48)

14.
Benchmark - the dark side
1.2
1
0.8
0.6
0.4
0.2
0
1
2
3
4
5
6
7
8
9
10

15.
Overhead
●
Contention – Retries, Aborts, Contention Manager …
●
STM Algorithm – Data structures, optimistic, pessimistic…
●
Semantic – Consistency model, Privatization…
●
Instrumented Memory access – Linear overhead on every read/write

16.
Static analysis Optimizations
1. Avoiding instrumentation of accesses to immutable and
transaction-local memory.
2. Avoiding lock acquisition and releases for
local memory.
thread-
3. Avoiding readset population in read-only transactions.

17.
Novel Static analysis
Optimizations
Y. Afek, G. Korland, and A. Zilberstein,
“Lowering STM Overhead with Static Analysis”, LCPC'10
1. Reduce amount of instrumented memory reads using load
elimination.
2. Reduce amount of instrumented memory writes using scalar
promotion.
3. Avoid writeset lookups for memory not yet written to.
4. Avoid writeset record keeping for memory that will not be read.
5. Reduce false conflicts by Transaction re-scoping.
...

18.
Benchmarks – K-Means

19.
We still need
Fine-Grained
Concurrent Data Structures

20.
e.g. Pool
• P1
• Get( )
• Put(x)
• C2
• P2
•.
•.
•.
• C1
• Put(y)
• Get( )
• Pn • Put(z)
• Get( )
• pool
•.
•.
•.
• Cn

21.
Java - pools
1. SynchronousQueue/Stack -
pairing up function without buffering.
Producers and consumers wait for one another
labilty.
/FIFO
Sca
LIFO and leave,
mited
● Li
2. LinkedBlockingQueuet- Producers put their value
' need
n
Consumers wait l does become available.
for a value to
● Poo
3. ConcurrentLinkedQueue - Producers put their value and leave,
Consumers return null if the pool is empty.

22.
ED-Tree
Scalable Producer-Consumr Pools Based on Elimination-Diffraction Trees
(Y. Afek, G. Korland, M. Natanzon, N. Shavit)
:
ucture
● Merge
ee Str
ng-Tr
fracti
● Dif
ach)
d Zem
cture
an
havit
e Stru
(S
n-Tre
inatio
● Elim
itou)
nd Tou
ueue
a v it a
(Sh
kingQ
Bloc
ed
● Link

23.
Performance

24.
What about other cases?

25.
Do we really need Linearizability?

26.
Can we make it more formal?

27.
The solution:
Relax the Linearizability Requirements
Y. Afek, G. Korland, and A. Yanovsky,
“Quasi-Linearizability: relaxed consistency for improved concurrency”,
OPODIS'10

28.
e.g. Task Queue
Tail
Head
Task
Task Consumers
Task
Task
Task
Task
Task Producers

29.
K-Quasi Task Queue
k
Tail
Head
Task
Task
Task
Task
Consumer
Task
Task
Task
Consumer
Task
Task

30.
Quasi Linearizable Definition
H’
1
2
3
4
5
6
H
4
1
2
3
5
6
Distance 3

31.
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