computer laboratory practical non-blocking linked lists tim harris [email protected] computer...
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Computer Laboratory
Overview: lists using CAS
• Insert 20:
H 10 30 T
20
30 20
10 30
20
30 20
Computer Laboratory
Overview: lists using CAS
• Insert 20:
H 10 30 T
20
30 20
25
30 25
10 30
20
30 20
25
30 25
Computer Laboratory
Overview: lists using CAS
• Delete 10:
H 10 30 T
10 30
H 10 30
10 30
Computer Laboratory
Overview: lists using CAS
• Delete 10 & insert 20:
H 10 30 T
10 30
H 10 30
10 30
20
30 20
H 10 30
10 30
H 10 30
10 30
20
30 20
Computer Laboratory
What can you do?
• Stronger primitives, e.g. DCAS
H 10
10 30 30 XX
H 10
10 30 30 XX30 T
Computer Laboratory
What can you do?
• Extra indirection:
H 10 30 T
30 1010 b
10 d
b10 30
30 10
10 d
b
caH 10
10 b
a
Computer Laboratory
Logical vs physical deletion
• Use a ‘spare’ bit to indicate logically deleted nodes:
H 10 30 T
20
10 30
30 30X
30 20H 10 30
20
10 30
30 30X
30 20
Computer Laboratory
H
Storage management
• Must control memory re-use while
threads hold pointers to it
H 10 30 T10 30
Computer Laboratory
Storage management (2)
Time
A
B
C
• Ref counting, tracing GC, time-based re-use
Add object toA’s deferred
free list
A finishes.C not complete:
can’t free object yet
Add object toC’s deferred
free listC finishes
A can now re-usethe object it removed:
B&C can’t havepointers to itDelayed threads
can prevent anyre-use
Computer Laboratory
Storage management (3)
• Also need to consider visibility of updates
H 10 30 T
20
30 20
Write-write
10 30
20
30 20Write-write
Computer Laboratory
Storage management (4)
• …and re-ordering of dependent reads
H 10 30 T
2020
10 30
while (val < seek) {
p = p->next;
val = p->val;
}
val = ???
Computer Laboratory
Random insert/deletePer-
thre
ad
CPU
-tim
e /
s
Valois (ref-counted)
New (ref-counted)
Valois
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Number of threads
Valois, ref-counting
New, ref-counting
Valois
New
Mutex
Computer Laboratory
Random insert/delete (2)Per-
thre
ad
CPU
-tim
e /
s
Valois (ref-counted)
New (ref-counted)
Valois
Number of threads
Valois, ref-counting
New, ref-counting
Valois
New
Mutex
0
2
4
6
8
10
12
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Mutex
Valois
New
Computer Laboratory
0
500
1000
1500
2000
2500
3000
3500
10 100 1000 10000 100000
Successful insertionsO
ccu
ran
ces
Duration / cycles
Mutex
New
Valois
Computer Laboratory
Unsuccessful insertions
Duration / cycles
Mutex
New
0
500
1000
1500
2000
2500
3000
3500
10 100 1000 10000 100000
New
Mutex
Valois
Occ
ura
nce
s
Computer Laboratory
Delete greater-than
H 10 30 T
• DeleteGE 20
10 30
20
• Insert 20
30 T
T TX
• Insert 30
30?
Computer Laboratory
Delete greater-than (2)
H 10 30 T
• Insert 20:
3020
T 20X
30 T
3020
T 20X