Detection of Asynchronous Message Passing Errors Using Static Analysis

1. Detection of Asynchronous Message Passing Errors Using Static Analysis Maria Christakis National Technical University of Athens, Greece Joint work with Kostis Sagonas

2. Concurrency

3. Interprocess communication • Synchronized shared structures • Synchronous message passing on typed channels • Asynchronous message passing

4. Erlang • Strict, dynamically typed, functional Concurrency model: • User-level processes • Asynchronous message passing

5. Agenda

6. Agenda

7. Agenda

8. Postman • Erlang VM

9. House • Process

10. Address • Process identifier

11. Mailbox • Process mailbox

12. Mail • Any valid Erlang term

13. Building a house Pid = spawn(Fun)

14. Sending mail Pid ! Msg

15. Receiving mail receive p1 -> e1; … pn -> en end

16. Receiving mail msg1 receive p1 -> e1; … pn -> en end msg2 msg3

17. Receive with no messages • Possible deadlock

18. Receive of the wrong kind • Mailbox overflow

19. Receive with unneeded patterns • Unreachable code or serious functionality issue

20. Send nowhere received • Mailbox overflow

21. Message passing example -export([hello_world/0]). hello_world() -> Self = self(), Fun = fun() -> world(Self) end, Pid = spawn(Fun), register(world, Pid), world ! hello. world(Parent) -> receive hello -> Parent ! hi end.

22. DIscrepancy AnaLYZer for ERlang • Static analysis tool for finding discrepancies • Type errors • Exception-raising code • Unsatisfiable conditions • Redundancies • Race conditions • Why Dialyzer?

23. The analysis: pros • Sound for defect detection

24. The analysis: pros • Automatic

25. The analysis: pros • Fast and scalable

26. The analysis: cons • Sound for defect detection

27. The analysis: a 3-step process

28. The analysis: a 3-step process

29. The analysis: a 3-step process

30. 1. Information • CFGs • Escape analysis • Inter-modular call graph • Sharing/alias analysis • Type information

31. 1. Information -export([hello_world/0]). hello_world() -> Self = self(), Fun = fun() -> world(Self) end, Pid = spawn(Fun), register(world, Pid), world ! hello. world(Parent) -> receive hello -> Parent ! hi end. • Call graph

32. 2. Communication graph blah

33. 2. Communication graph -export([hello_world/0]). hello_world() -> Self = self(), Fun = fun() -> world(Self) end, Pid = spawn(Fun), register(world, Pid), world ! hello. world(Parent) -> receive hello -> Parent ! hi end.

34. 3. Errors -export([hello_world/0]). hello_world() -> Self = self(), Fun = fun() -> world(Self) end, Pid = spawn(Fun), register(world, Pid), world ! hello. world(Parent) -> receive hello -> Parent ! hi end. The message will never be received

35. 3. Errors • receive blah • receive No messages are sent to the process

36. 3. Errors • 43 receive {A, 42} when is_atom(A) -> ok; foo -> … end • Infimum: {gazonk, 42} The pattern will never match messages sent to the process

37. Optimizations • Control-flow graph minimization • Avoiding repeated traversals • Avoiding redundant traversals

38. False alarm avoidance • BIFs • Sharing/alias analysis

39. False negatives -export([hello_world/0]). hello_world() -> Self = self(), Fun = fun() -> world(Self) end, Pid = spawn(Fun), register(world, Pid), world ! hello. world(Parent) -> receive hello -> Parent ! hi, world(Parent) end.

40. Experimental evaluation

41. Performance

42. Concluding remarks

43. Future work

44. Future work

45. Future work