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Self-referential error trace exploration: _TEPosition and _TETrace operators

See original GitHub issue

For the lack of better naming, support self-referential error trace exploration s.t. a trace expression can reference to the actual trace (TETrace). This would significantly increase the expressiveness of trace expressions:

Current state number in error-trace (depends on 43e2b745537726bb0b4f8ad75d52cec6edd5f1d0):

TEStateNumber ==
IF TLCGet("level") + 1 > Len(TETrace) THEN Len(TETrace) ELSE TLCGet("level") + 1

and a vector clock (“Clock”), activate process in state (“Host”), and a sequence counter (“Timestamp”) from the pc variable:

Clock ==
LET self(n) == IF n = 1 THEN "Init" ELSE LET this == TETrace[n].pc
                                             prev == TETrace[n - 1].pc
                                         IN CHOOSE p \in DOMAIN prev : prev[p] # this[p]
    lclock(n) == [p \in DOMAIN pc |-> IF p = self(n) THEN 1 ELSE 0]
    merge(F, G) == [d \in DOMAIN F |-> F[d] + G[d]]
IN LET clock[i \in DOMAIN TETrace] == IF i = 1 
                                      THEN lclock(i)
                                      ELSE merge(clock[i-1], lclock(i))
   IN clock[TEStateNum]

Timestamp == TEStateNumber * 1000

Host == LET n == TEStateNumber
        IN IF n = 1 
           THEN "Init"
           ELSE LET this == TETrace[n].pc
                    prev == TETrace[n - 1].pc
                IN CHOOSE p \in DOMAIN prev : prev[p] # this[p]

State 2: <next_1553899086803916000 line 105, col 3 to line 164, col 2 of module TE>
/\ expected = (w1 :> 0 @@ w2 :> 0 @@ w3 :> 0)
/\ tail = 0
/\ a3Clock = {"w1":1, "w2":0,"w3":0}
/\ pc = (w1 :> "casA" @@ w2 :> "deq" @@ w3 :> "deq")
/\ a1Host = w1
/\ disk = <<1, 2>>
/\ history = <<>>
/\ result = (w1 :> FALSE @@ w2 :> FALSE @@ w3 :> FALSE)
/\ a1Timestamp = 2000
/\ head = 2

State 3: <next_1553899086803916000 line 166, col 3 to line 225, col 2 of module TE>
/\ expected = (w1 :> 1 @@ w2 :> 0 @@ w3 :> 0)
/\ tail = 1
/\ Clock = {"w1":2, "w2":0,"w3":0}
/\ pc = (w1 :> "wt" @@ w2 :> "deq" @@ w3 :> "deq")
/\ Host = w1
/\ disk = <<1, 2>>
/\ history = <<>>
/\ result = (w1 :> TRUE @@ w2 :> FALSE @@ w3 :> FALSE)
/\ Timestamp = 3000
/\ head = 2
....

(https://gist.github.com/lemmy/3e1c7226e9aa342bc04df6888b46a686)

This trace can be fed to TSViz or ShiViz almost verbatim (syntax no legal JSON) with the following regex:

^(State ){0,1}(\d*): <(?<event>.*)>\n\/\\ expected = (?<expected>.*)\n\/\\ tail = (?<tail>.*)\n\/\\ a3Clock = (?<clock>.*)\n\/\\ pc = (?<pc>.*)\n\/\\ a1Host = (?<host>.*)\n\/\\ disk = (?<disk>.*)\n\/\\ history = (?<history>.*)\n\/\\ result = (?<result>.*)\n\/\\ a1Timestamp = (?<timestamp>.*)\n\/\\ head = (?<head>.*)

D23LmvTUcAAq7b1 jpg:large D23LnsMUkAAxVV- jpg:large

Alternatively:

a) Enhance org.lamport.tla.toolbox.tool.tlc.model.TraceExpressionModelWriter to add a __trace_var_state_number variable to the generated init and next in TE.tla => Disadvantage: Unnecessarily clutters the error trace when a user doesn’t care (requires filtering at the Toolbox layer).

b) By default add TEStateNumber == IF TLCGet("level") + 1 > Len(TETrace) THEN Len(TETrace) ELSE TLCGet("level") + 1 operator to generated TE.tla => Doesn’t work because of #266

c) Generate TEStateNumber(ignored) == ... (bogus/unused parameter) => Dirty Hack

A completely different angle is to (formally) introduce a next and previous/before operator as e.g. described in “Temporal Verification of Reactive Systems: Safety” Pnuelli & Manna on page 43ff. A past/next operator would e.g. allow users to (recursively) evaluate expressions over all predecessor/successor states.

Depends on: #265, #266 Resulted in: #262, #264

Issue Analytics

State:
Created 4 years ago
Comments:5 (5 by maintainers)

Top GitHub Comments

1reaction

lemmycommented, Jun 27, 2019

Part I

ErrorTraceExplorationP1

Host == LET n == _TEPosition
        IN IF n = 1 
           THEN "Init"
           ELSE LET this == _TETrace[n].pc
                    prev == _TETrace[n - 1].pc
                IN CHOOSE p \in DOMAIN prev : prev[p] # this[p]

Clock ==
LET self(n) == IF n = 1 THEN "Init" ELSE LET this == _TETrace[n].pc
                                             prev == _TETrace[n - 1].pc
                                         IN CHOOSE p \in DOMAIN prev : prev[p] # this[p]
    lclock(n) == [p \in DOMAIN pc |-> IF p = self(n) THEN 1 ELSE 0]
    merge(F, G) == [d \in DOMAIN F |-> F[d] + G[d]]
IN LET clock[i \in DOMAIN _TETrace] == IF i = 1 
                                      THEN lclock(i)
                                      ELSE merge(clock[i-1], lclock(i))
   IN ToJSONObject(clock[_TEPosition])


zExpected == IF Host = "Init" THEN 0 ELSE expected[Host]

zResult == IF _TEPosition = 1 THEN FALSE ELSE result[Host]

Part II

ErrorTraceExplorationP2

See https://bestchai.bitbucket.io/shiviz/ and https://queue.acm.org/detail.cfm?id=2940294

^(State ){0,1}(\d*): <(?<event>(?!Initial predicate).*)>\n\/\\ expected = (.*)\n\/\\ tail = (?<tail>.*)\n\/\\ Clock = (?<clock>.*)\n\/\\ pc = (.*)\n\/\\ disk = (?<disk>.*)\n\/\\ pages = (?<pages>.*)\n\/\\ Host = (?<host>.*)\n\/\\ history = (?<history>.*)\n\/\\ zResult = (?<result>.*)\n\/\\ result = (.*)\n\/\\ zExpected = (?<expected>.*)\n\/\\ head = (?<head>.*)

error-trace.txt

ToJSONObject

!!! Please read https://github.com/tlaplus/tlaplus/issues/267#issuecomment-483898426 first !!!

For ToJSONObject operator see https://github.com/tlaplus/tlaplus/issues/159#issuecomment-481901751.

RegExp

Alternatively, use ToJSONObject operator below, copy&paste regular error-trace to error-trace.txt and “massage” output with the regular expression:

ToJSONObject(F) == Image([ d \in DOMAIN F |-> "'" \o ToString(d) \o "':'" \o ToString(F[d]) \o "'" ])

cat error-trace.txt | sed -e 's/"'\''\([[:alnum:]]*\)'\'':'\''\([[:digit:]]\)*'\''"/"\1":\2/g'

0reactions

lemmycommented, Jul 21, 2020

The ShiViz paper (https://dl.acm.org/doi/10.1145/3375633) links to this issue.

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