Presentation of IWST16, Prag Video: https://youtu.be/jQQqsrfRgjo

1. A PROMISING APPROACH
TO DEBUGGING REMOTE
PROMISES
2016
Max Leske
Andrei Chiș
Oscar Nierstrasz

2. DISCLAIMER

3. MOTIVATION

4. request file list
display file list
receive file list

5. request file list
display file list
receive file list

6. request file list
PROMISE
receive file list
use
use
continue

7. fileListPromise := [ self getFileList ] promise.
fileListPromise value.
…

8. request file list
what happened?

9. stack tracestack trace
descriptiondescription
NULLNULL
what happened?
exception object

10. IDEA

11. 1
sender
receiver
1
Object
Context
CompiledMethod
1
method
Process
suspendedContext
1

12. sender
nil
sender
Process
suspendedContext

13. sender
nil
sender
Process1
suspendedContext
sender
nil
sender
Process2
suspendedContext

14. sender
Process1+2
suspendedContext
sender
sender
sender
sender
nil

15. DEMO

16. MEMORY

17. object header: 64 bits
2
pinned / immutable
slots
8
identity hash
22
format
5
class index
22
unused
2
garbage collection
3

18. object header
extended header
slot 0 slot 1
slot 2 …
object

19. object header
Context
method
closureOrNil
stackp
receiver
sender pc
16 / 56 variable slots
no extended header required
96 / 256 bytes per instance

20. ∑ ≪ 100 000 ~ 1000
small contexts: 96 kB
large contexts: 256 kB
* 2 (reification)
small contexts: 192 kB
large contexts: 512 kB
estimated upper bounds

21. memory consumption of contexts:

22. object graph (simplified)
garbage collector
partially collected

23. garbage collector
not collected
copy

24. memory consumption of object graph:
?

25. PERFORMANCE

26. fileListPromise := [ self getFileList ] promise.
fileListPromise value.
…
copy process full copy
reify contexts

27. copying stack of 100 000 frames
0 MS
125 MS
250 MS
375 MS
500 MS
SMALL CONTEXTS LARGE CONTEXTS SMALL CONTEXTS LARGE CONTEXTS
with GC without GC

28. performance:

29. REMOTE
COMMUNICATION

30. protocol?
SeamlessSeamless

31. DEBUGGING
serialised process
local copy of process
proxies

32. THREADS
promises
events
asynchronous messages (actors)
asynchronous network requests

33. request file list
what happened?
copy process full copy
reify contexts
Process1+2
suspendedContext
sender
nil
sender
sender
sender
sender