Slides for our ECOOP 2018 paper on efficient, incremental Checkpoint/Rollback in the JVM

1. Crochet: Checkpoint and Rollback via
Lightweight Heap Traversal on Stock JVMs
Jonathan Bell and Luís Pina
{bellj / lpina2}@gmu.edu
George Mason University
European Conference on Object-Oriented Programming
July 20, 2018

2. Fuzzing a method
01
02 String cmd ;
03
04 ... // Lots of uninteresting code
05
06
07
08 methodToFuzz(cmd);
09
10
11
12
13
14
15
2

3. Fuzzing a method
01
02 String cmd ;
03
04 ... // Lots of uninteresting code
05 while (true) {
06 cmd = mutate(cmd);
07
08 methodToFuzz(cmd);
09
10
11
12 }
13
14
15
3

4. Fuzzing a method
01
02 String cmd ;
03
04 ... // Lots of uninteresting code
05 while (true) {
06 cmd = mutate(cmd);
07 try {
08 methodToFuzz(cmd);
09 } catch (Throwable t) {
10 generateTest(cmd);
11 }
12 }
13
14
15
4

5. Fuzzing a method
Example test
generateTest("SET key val")
5

6. Fuzzing a method
Example test
generateTest("SET key val")
methodToFuzz("SET key val")
6

7. Fuzzing a method
Example test
generateTest("SET key val")
methodToFuzz("SET key val")
3
7

8. Fuzzing a method
Example test
generateTest("SET key val")
methodToFuzz("SET key val")
3
8

9. Fuzzing a method
State is a problem
Bu er:
methodToFuzz("SET key val")
SET key val
9

10. Fuzzing a method
State is a problem
Bu er:
methodToFuzz("SET key val")
SET key val
methodToFuzz("SET key val")
SET key val
10

11. Fuzzing a method
State is a problem
Bu er:
methodToFuzz("SET key val")
SET key val
methodToFuzz("SET key val")
SET key val
methodToFuzz("SET key val")
SET key val
7
11

12. Fuzzing a method
State is a problem
Bu er:
methodToFuzz("SET key val")
SET key val
methodToFuzz("SET key val")
SET key val
methodToFuzz("SET key val")
SET key val
7
generateTest("SET key val")
12

13. Fuzzing a method
Restart with fresh state
Native Restart
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0timetocomplete(sec)
41.52
78.33
Short fuzz run (110 FTP commands)
13

14. Checkpoint/Rollback
Bu er:
checkpoint
14

15. Checkpoint/Rollback
Bu er:
checkpoint
15

16. Checkpoint/Rollback
Bu er:
checkpoint
methodToFuzz("SET key val")
SET key val
16

17. Checkpoint/Rollback
Bu er:
checkpoint
methodToFuzz("SET key val")
SET key val
rollback
17

18. Checkpoint/Rollback
Bu er:
checkpoint
methodToFuzz("SET key val")
SET key val
rollback
18

19. Checkpoint/Rollback
Bu er:
checkpoint
methodToFuzz("SET key val")
rollback
19

20. Checkpoint/Rollback
Bu er:
checkpoint
methodToFuzz("SET key val")
rollback
methodToFuzz("SET key val")
20

21. Checkpoint/Rollback
Bu er:
Crochet.checkpoint()
methodToFuzz("SET key val")
Crochet.rollback()
methodToFuzz("SET key val")
Crochet
I No JVM changes (Excludes fork)
I Checkpoint/rollback dynamically
I E cient (Excludes CRIU)
I Low overhead (Excludes STMs)
21

22. Crochet
E cient
DeepClone CRIU CROCHET
Checkpoint Technique
1.0
1.1
1.2
1.3
1.4
1.5
1.6Timetocomplete(normalizedtonative)
Access percent of TreeMap after checkpoint
10% 25% 50% 100%
22

23. Checkpoint/Rollback
Bu er:
Crochet.checkpoint()
methodToFuzz("SET key val")
Crochet.rollback()
methodToFuzz("SET key val")
Crochet
I No JVM changes (Excludes fork)
I Checkpoint/rollback dynamically
I E cient (Excludes CRIU)
I Low overhead (Excludes STMs)
23

24. Crochet
Low overhead
Native Restart Crochet Crochet c/r
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0timetocomplete(sec)
41.52
78.33
42.69 43.77
Short fuzz run (110 FTP commands)
24

25. Checkpoint/Rollback
Bu er:
Crochet.checkpoint()
methodToFuzz("SET key val")
Crochet.rollback()
methodToFuzz("SET key val")
Crochet
I No JVM changes (Excludes fork)
I Checkpoint/rollback dynamically
I E cient (Excludes CRIU)
I Low overhead (Excludes STMs)
25

26. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
26

27. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
27

28. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root.method()
28

29. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
v = 1
root.method()
29

30. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
v = 1
root.method()
v = 1 v = 1
v = 1
30

31. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
v = 1
31

32. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
v = 1 B.method()
32

33. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
v = 1
33

34. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
v = 1
F.method()
34

35. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
35

36. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
36

37. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
v = 2
37

38. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()v = 1
root
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
v = 2
root.method()
38

39. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
v = 2
root.method()
39

40. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
40

41. Lazy Heap Traversal
Tracked object information:
Version 0, 1, . . .
Snapshot Object state to-be-restored, if any
State normal or proxy (Checkpoint/Rollback)
Invariants:
1. Identity: Versions are unique
2. Total Order: Versions increase monotonically
3. Continuity: Proxies mediate access during traversal
41

42. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
42

43. Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
43

44. Applications
I Checkpoint/Rollback
I Fuzz testing
I Code generation
I Debugging
I As application service
I Dynamic Software Update
I Proxies update objects lazily as reached after update
I Rubah
I Smalltalk become:
I a.become(b)
I All refs to a become refs to b, and vice-versa
I Proxies update refs lazily
I Dynamic AOP
I Proxies can add methods, enabling around advices
I Per object point-cuts
44

45. Goals
Crochet
I No JVM changes (Excludes fork)
I E cient (Excludes CRIU) 3
I Checkpoint/rollback dynamically
I Low overhead (Excludes STMs)
45

46. Implementation
Bytecode rewriting
01 class List {
02 List next; int i;
03
04 int sum()
05 { return i + next.sum(); }
06
07
08
09
10
11
12
13 }
46

47. Implementation
Bytecode rewriting
01 class List {
02 List next; int i;
03
04 int sum()
05 { return i + next.sum(); }
06
07 List $$snapshot; int $$version; // But no status!
08
09
10
11
12
13 }
47

48. Implementation
Bytecode rewriting
01 class List {
02 List next; int i;
03
04 int sum()
05 { return i + next.sum(); }
06
07 List $$snapshot; int $$version; // But no status!
08 void $$onReadWrite(); // Empty
09 void $$onCheckpoint(int version); // Turn into proxy
10 void $$onRollback(int version); // Turn into proxy
11
12 void $$copyFieldsTo(List dest);
13 }
48

49. Implementation
Bytecode rewriting
01 class List {
02 List next; int i;
03
04 int sum()
05 { next.$$onReadWrite(); return i + next.sum(); }
06
07 List $$snapshot; int $$version; // But no status!
08 void $$onReadWrite(); // Empty
09 void $$onCheckpoint(int version); // Turn into proxy
10 void $$onRollback(int version); // Turn into proxy
11
12 void $$copyFieldsTo(List dest);
13 }
49

50. Implementation
Proxies
01 class $$ListProxy extends List {
02 // No extra fields => Proxy has same size
03
04
05
06
07
08
09 void $$onReadWrite(); // Snap, propagate, revert proxy
10 void $$onCheckpoint(int version); // Update version
11 void $$onRollback(int version); // Update version
12
13
14 }
50

51. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
51

52. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
52

53. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
53

54. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getInt(p, 0);
06 int proxy_klass = Unsafe.getInt(p, 4);
54

55. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getInt(p, 0);
06 int proxy_klass = Unsafe.getInt(p, 4);
07 Unsafe.setInt( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
55

56. Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getInt(p, 0);
06 int proxy_klass = Unsafe.getInt(p, 4);
07 Unsafe.setInt( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
56

57. Goals
Crochet
I No JVM changes (Excludes fork) 3
I E cient (Excludes CRIU) 3
I Checkpoint/rollback dynamically
I Low overhead (Excludes STMs)
58

58. Root reference collection
I Static fields of loaded classes
I Instrument class loading
I Live thread objects
I Instrument thread creation
I Call stack (function args, local vars)
I Use standard debugger API
I Operand stack (bytecode instruction operands)
I Tricky, gets compiled away
I Instrument end of basic blocks to dump current stack when a
special flag is set
59

59. Multithreading
I Crochet is thread-safe
I Operations use Compare-And-Swap to synchronize
I Rollback not idempotent, needs locks
I Root collection must be done with threads stopped
I Barrier-sync to checkpoint/rollback whole heap
Thread 1
Thread 2
Thread 3
Checkpoint
Start
Crochet
Collect roots
Install proxies
Establish invariants
Checkpoint
Done
Thread 1
60

60. Goals
Crochet
I No JVM changes (Excludes fork) 3
I E cient (Excludes CRIU) 3
I Checkpoint/rollback dynamically 3
I Low overhead (Excludes STMs)
61

61. Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
62

62. Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
fast execution
(<300ms)
63

63. Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
fast execution (<1s)
large dump(>3GB)
64

64. Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
reflection
class loading
65

65. Goals
Crochet
I No JVM changes (Excludes fork) 3
I E cient (Excludes CRIU) 3
I Checkpoint/rollback dynamically 3
I Low overhead (Excludes STMs) 3
66

66. Crochet
Limitations
I Not checkpointed/rolled-back:
I Native code and references only held inside native code
I Class loaders
I State kept outside of the JVM (e.g., files, sockets)
I Reliance on “unsupported” sun.misc.Unsafe
I Eager checkpoint/rollback of arrays and some classes (e.g.,
java.lang.Exception)
67

67. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
68

68. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getLong(p, 0);
06 int proxy_klass = Unsafe.getLong(p, 4);
07 Unsafe.setLong( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
57
Stock JVM
69

69. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getLong(p, 0);
06 int proxy_klass = Unsafe.getLong(p, 4);
07 Unsafe.setLong( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
57
Stock JVM
Multithreading
I Crochet is thread-safe
I Operations use Compare-And-Swap to synchronize
I Rollback uses locks due to non-idempotent
I Root collection must be done with threads stopped
I Barrier-sync to checkpoint/rollback whole heap
Thread 1
Thread 2
Thread 3
Checkpoint
Start
Crochet
Collect roots
Install proxies
Establish invariants
Checkpoint
Done
Thread 1
61
Dynamic checkpoint/rollback
70

70. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getLong(p, 0);
06 int proxy_klass = Unsafe.getLong(p, 4);
07 Unsafe.setLong( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
57
Stock JVM
Multithreading
I Crochet is thread-safe
I Operations use Compare-And-Swap to synchronize
I Rollback uses locks due to non-idempotent
I Root collection must be done with threads stopped
I Barrier-sync to checkpoint/rollback whole heap
Thread 1
Thread 2
Thread 3
Checkpoint
Start
Crochet
Collect roots
Install proxies
Establish invariants
Checkpoint
Done
Thread 1
61
Dynamic checkpoint/rollback
Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
63
Low overhead
71

71. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getLong(p, 0);
06 int proxy_klass = Unsafe.getLong(p, 4);
07 Unsafe.setLong( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
57
Stock JVM
Multithreading
I Crochet is thread-safe
I Operations use Compare-And-Swap to synchronize
I Rollback uses locks due to non-idempotent
I Root collection must be done with threads stopped
I Barrier-sync to checkpoint/rollback whole heap
Thread 1
Thread 2
Thread 3
Checkpoint
Start
Crochet
Collect roots
Install proxies
Establish invariants
Checkpoint
Done
Thread 1
61
Dynamic checkpoint/rollback
Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
63
Low overhead
Applications
I Checkpoint/Rollback
I Fuzz testing
I Code generation
I As application service
I etc
I Dynamic Software Update
I Proxies update objects lazily as reached after update
I Rubah
I Smalltalk become:
I a.become(b)
I All refs to a become refs to b, and vice-versa
I Proxies update refs lazily
I Dynamic AOP
I Proxies can add methods, enabling around advices
45
Many applications
72

72. Conclusion
Lazy Heap Traversal
v = 0
root
v = 0
A
v = 0
B
v = 0
C
v = 0
E
v = 0
F
v = 0
G
v = 0
H
v = 0
I
v = 0
J
Crochet.checkpoint()
root.method()
v = 1 v = 1
B.method()v = 1
B
v = 1
F.method()
v = 1
v = 1
F
Crochet.rollback()
root.method()
v = 2
v = 2
v = 2
v = 2
root
41
E cient
lazy heap traversal
Implementation
Proxy on/o
01 List l = new List ();
02 $$ListProxy p = new $$ListProxy ();
_mark _klass i next
_mark _klass i next
03 Field f = List.class.getField("i");
04 int off_i = Unsafe.getOffset(f); // 8
05 int proxy_mark = Unsafe.getLong(p, 0);
06 int proxy_klass = Unsafe.getLong(p, 4);
07 Unsafe.setLong( l , 4, proxy_klass );
08 assert(l instanceof $$ListProxy);
57
Stock JVM
Multithreading
I Crochet is thread-safe
I Operations use Compare-And-Swap to synchronize
I Rollback uses locks due to non-idempotent
I Root collection must be done with threads stopped
I Barrier-sync to checkpoint/rollback whole heap
Thread 1
Thread 2
Thread 3
Checkpoint
Start
Crochet
Collect roots
Install proxies
Establish invariants
Checkpoint
Done
Thread 1
61
Dynamic checkpoint/rollback
Crochet
Performance
avrora
batik
eclipse
fop h2 jython
luindex
lusearch
pmd
sunflow
tomcat
tradebeans
xalan
AVG
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
timetocomplete(normalizedtonative)
DaCapo Benchmark
Crochet Crochet C/R CRIU
63
Low overhead
Applications
I Checkpoint/Rollback
I Fuzz testing
I Code generation
I As application service
I etc
I Dynamic Software Update
I Proxies update objects lazily as reached after update
I Rubah
I Smalltalk become:
I a.become(b)
I All refs to a become refs to b, and vice-versa
I Proxies update refs lazily
I Dynamic AOP
I Proxies can add methods, enabling around advices
45
Many applications
Fork
us
on
G
itH
ub
73

73. Conclusion
Fork
us
on
G
itH
ub
Crochet
I No JVM changes
I Use bytecode rewriting and standard debug API
I E cient
I Copy-on-access through thread-safe lazy heap traversal
I Checkpoint/rollback dynamically
I Just barrier-sync threads
I Low overhead
I 6% when not using checkpoint/rollback, 49% otherwise
I Beats alternative approaches (CRIU, STM, DeepClone)
I Many applications
I Checkpoint/rollback in itself and to enable other techniques
I Specalized proxies for: become:, per-object dynamic AOP, etc.
I Get Crochet: https://github.com/gmu-swe/crochet
74