InvariantChecker.scala 8.32 KB
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package de.tum.workflows.toz3

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import java.util.HashMap
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import scala.annotation.tailrec

// labeled directed edge
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import com.microsoft.z3.Context
import com.microsoft.z3.Status
import com.typesafe.scalalogging.LazyLogging
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import de.tum.workflows.Encoding
import de.tum.workflows.Implicits._
import de.tum.workflows.Preconditions
import de.tum.workflows.blocks._
import de.tum.workflows.foltl.FOLTL._
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import de.tum.workflows.foltl.FormulaFunctions
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import de.tum.workflows.ltl.FOTransformers
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import de.tum.workflows.Utils
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import de.tum.workflows.foltl.Properties
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case class InvProperties(stubborn:Boolean, eliminateAux:Boolean) { }
object InvProperties {
  val DEFAULT = InvProperties(true, true)
}

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object InvariantChecker extends LazyLogging {
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  val TIMEOUT = 60000 // in milliseconds
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  def checkOnZ3(f: Formula) = {
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    val (time, res) = Utils.time {
      // Set up Z3
      val cfg = new HashMap[String, String]()
      cfg.put("timeout", TIMEOUT.toString())
      val ctx = new Context(cfg)
  
      //    val qe = ctx.mkTactic("qe")
      //    val default = ctx.mkTactic("smt")
      //    val t = ctx.andThen(qe, default)
      //    val s = ctx.mkSolver(t)
  
      val s = ctx.mkSolver()
      
      // Can only check universal things
      val neg = Neg(f).simplify()
  
      // univfree is now in E*, so can be solved as SAT Problem
      val stripped = FormulaFunctions.stripQuantifiers(neg)
  
      // val prefix = FormulaFunctions.collectQuantifiersSub(univfree)
      val satform = FOTransformers.eliminatePredicates(stripped)
  
      // Checking QFree
      s.add(Z3QFree.translate(satform, ctx))
  
      // Send to z3
      val c = s.check()
      if (c == Status.UNKNOWN) {
        logger.info(s"Z3 status unknown: ${s.getReasonUnknown()}")
      }
      if (c == Status.SATISFIABLE) {
//        logger.info(s"Z3 status satisfiable")
        //      logger.info(s"${s.getModel()}")
      }
      (c, s)
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    }
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    logger.info(s"Z3 call took $time ms")
    res
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  }
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  def checkBlockInvariant(spec:Spec, b: SimpleBlock, pre: Formula, post: Formula, isfirst: Boolean, properties:InvProperties) = {
    val precond = Preconditions.abstractPrecondition(post, b, spec, properties)
    
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    // TODO: do we do this here?
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    val firstprecond = if (isfirst) {
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      precond.assumeEmpty(spec.w.sig.preds.map(_.name).toList)
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    } else { precond }
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    val noinfprecond = if (isfirst) {
      firstprecond.assumeEmpty(List(Properties.INFNAME))
    } else { firstprecond }
    
    val z3simpednewinv = Z3QFree.simplifyUniv(noinfprecond)
    val gained = noinfprecond.toString().length() - z3simpednewinv.toString().length()
    logger.info(s"Invariant shrunken by $gained chars")
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    //      val test1 = inv.toPrenex()
    //      val test2 = stubprecond.toPrenex()

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    val f = Implies(pre, z3simpednewinv)
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    logger.info(s"Checking invariant implication for $b")

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    (checkOnZ3(f.simplify()), z3simpednewinv)
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  }
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  def checkInvariantFPLabelling(spec: Spec, inv: Formula, properties:InvProperties) = {
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    val graph = Encoding.toGraph(spec.w)
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    type Node = graph.NodeT
    type Edge = graph.EdgeT

    @tailrec
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    def checkInvariantRec(labellist: List[Map[Node, Formula]], provenlist: List[Set[Edge]]): (Boolean, List[Map[Node, Formula]], List[Set[Edge]]) = {
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      val labels = labellist.head
      val proven = provenlist.head
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      // check if done, i.e. all edges proven
      val toProve = (graph.edges -- proven)
      if (toProve.isEmpty) {
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        logger.info("Everything proven. Terminating.")
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        (true, labellist, provenlist)
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      } else {

        // take one edge to prove
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//        val next = toProve.head
        // take the edge with a minimum of following unproven edges excluding selfloops
//        val next = toProve.minBy(edge => ((edge.target.outgoing.filter(t => t.target != t.source) -- proven).size))
        // take the edge with maximum source node first
        val next = toProve.maxBy(edge => edge.source.value)
        
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        // try to prove
        val pre = labels(next._1)
        val post = labels(next._2)
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        val isfirst = !next._1.hasPredecessors
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        val ((status, solver), strengthened) = checkBlockInvariant(spec, next, pre, post, isfirst, properties)
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        if (status == Status.UNSATISFIABLE) {
          // Negation of implication unsat
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          // --> safe, continue with larger proven set.
          logger.info(s"Proven inductiveness for (${next._1} -> ${next._2}).")
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          checkInvariantRec(labels :: labellist, (proven + next) :: provenlist)
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        } else {
          // Negation of implication sat
          // --> unsafe, relabel incoming node, invalidate all proven guarantees for that node
          // check if relabelled invariant still satisfiable
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          // never relabel initial node
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          logger.info(s"Invariant not inductive, strengthening")
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          if (!isfirst) {
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            // check if strengthened -> old_inv else use conjunction
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//            val strengthened = Preconditions.abstractPrecondition(post, next, spec, properties)
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            val newinv = And(labels(next._1), strengthened).simplify()
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            val nostrangebindings = FormulaFunctions.checkBindings(newinv)
            if (!nostrangebindings) {
              logger.error("New invariant binds variables more than once")
              logger.error(s"Invariant would be $newinv")
            }
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            val newlabels = labels.updated(next._1, strengthened)
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            val invalidated = proven.filter(_._2 == next._1)
            
            val newproven = (proven -- invalidated) + next
  
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            val (status2, solver2) = checkOnZ3(Implies(newinv, False))
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            if (status2 == Status.SATISFIABLE) {
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              // Negation of newinv still sat, newinv does not imply false)
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              logger.info(s"Relabeling ${next._1}. Continuing.")
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              checkInvariantRec(newlabels :: labellist, newproven :: provenlist)
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            } else {
              logger.info(s"New invariant for ${next._1} not satisfiable. Terminating.")
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              (false, newlabels :: labellist, newproven :: provenlist)
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            }
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          } else {
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            logger.info("Would have to relabel initial node. Terminating.")
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            (false, labellist, provenlist)
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          }
        }
      }
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    }

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    // create labelling - FIXME: maybe use inv only for last
    val labels = (for (n <- graph.nodes) yield { n -> inv }).toMap
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    val (time, (result, labellings, proven)) = Utils.time { checkInvariantRec(labels, List(Set())) }
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    val dot1 = labellings.zip(proven).reverse
    val dot2 = dot1.map((tup) => Encoding.toDot(graph)(tup._1.map(t => (t._1, {
      if (t._2.opsize() <= 5000) t._2.pretty() else "TOO BIG"
    })), tup._2))
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    (result, graph, labellings.reverse, proven.reverse, dot2, time)
  }
  
  def checkInvariantFP(spec: Spec, inv: Formula, properties:InvProperties = InvProperties.DEFAULT) = {
    val (result, graph, afterlabels, proven, dot, time) = checkInvariantFPLabelling(spec, inv, properties)
    (result, dot)
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  }
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  def checkInvariantOnce(spec: Spec, inv: Formula, properties: InvProperties) = {
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    // Build graph
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    val graph = Encoding.toGraph(spec.w)
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    val msg = new StringBuilder()
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    msg ++= s"Trying to prove safe with invariant:\n\n${inv.pretty()}\n\n"
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    // Check all edges
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    val list = for (e <- graph.edges) yield {
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      // Check I -> WP[w](inv)
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      val b: SimpleBlock = e
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      // Special handling for first block
      // TODO: Replace by iteration
      val isfirst = !e.from.hasPredecessors
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      val ((res, solver), strengthened) = checkBlockInvariant(spec, b, inv, inv, isfirst, properties)
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      if (res != Status.UNSATISFIABLE) {
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        msg ++= s"Possibly unsafe: Block may not uphold invariant:\n\n${e.label}\n\n"
        if (res == Status.SATISFIABLE) {
          msg ++= "Satisfying model:\n"
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          msg ++= Z3.printModel(solver.getModel()).lines.map("  " + _).mkString("\n")
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        } else if (res == Status.UNKNOWN) {
          msg ++= s"Z3 result: $res (${solver.getReasonUnknown()})\n"
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        }
        msg ++= "\n"
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        logger.info(s"Could not prove invariant $inv")
        logger.info(s"Z3 status $res")
        logger.info(s"Block ${e.label} may not uphold it")
      }
      res == Status.UNSATISFIABLE
    }
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    val safe = list.reduceLeft(_ && _)
    if (safe) {
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      msg ++= s"Proven safe.\n"
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      logger.info(s"Workflow ${spec.w}\n proven safe for invariant:\n${inv.pretty()}")
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    }
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    (safe, msg)
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  }
}