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Retro AC Example for KeY

This is a an example how Retrospective Assertion Checking can be done with KeY. To be specific, the example is Quicksort, and we will show that the sorting is correct for as many recorded control flow traces as you want.

Just a demo, don't expect anything more.

Building

gradlew shadowJar

Recording

java -jar quicksort-main/build/libs/quicksort-main-all.jar 3 14 1 1455 -10

Then an array with the given numbers is sorted. The trace goes into trace-out/trace*.

Validating

Open KeY, navigate into trace-out/ and show the proof obligation.

Further Background

The instrumentation of Quicksort was done manually. It is not hard to implement automatic instrumentation: For C, we already implemented it. Apart form that, recording and validating can be done fully automatically. With the exact same pre- and post-condition, we can validate any traces for any sorting algorithm, not just quicksort. And we don't need loop invariants and the like.

Be aware that validation with KeY is not the most efficient thing to do. Try validating a trace from sorting an input array of 11 numbers, it still works fine, but takes about 6 minutes on my computer, includeing 4x pressing the "continue" button in KeY. The final proof for array input 3 14 1 1455 -10 3 4 1 9 -10 15 consists of about 34000 nodes. I would suggest starting with a smaller array as given in the recording section.

Directory Structure

  • quicksort/: Contains Quicksort.java, the manually instrumented quicksort implementation. The original implementation is one of the examples from the KeY project.
  • quicksort-main/: Contains a main method to run quicksort from command line arguments. Not instrumented.
  • tracer/: Contains the Trace.java implementation, used when tracing. To validate the trace, a different Trace.java is generated into trace-out/trace*.