.gitlab-ci.yml

@@ -25,7 +25,7 @@ grade:
   tags:
     - cs206
   image:
-    name: smarter3/moocs:reactive-actorbintree-2020-04-15
+    name: smarter3/moocs:concpar-lockfree-2020-03-24-2
     entrypoint: [""]
   allow_failure: true
   before_script:

build.sbt

@@ -1,24 +1,11 @@
-course := "reactive"
-assignment := "actorbintree"
-
-testOptions in Test += Tests.Argument(TestFrameworks.JUnit, "-a", "-v", "-s")
-parallelExecution in Test := false
-
-val akkaVersion = "2.6.0"
+course := "concpar"
+assignment := "lockfree"
 
 scalaVersion := "0.23.0-bin-20200211-5b006fb-NIGHTLY"
 
-scalacOptions ++= Seq(
-  "-feature",
-  "-deprecation",
-  "-encoding", "UTF-8",
-  "-unchecked",
-  "-language:implicitConversions"
-)
+scalacOptions ++= Seq("-language:implicitConversions", "-deprecation")
 
-libraryDependencies ++= Seq(
-  "com.typesafe.akka"        %% "akka-actor"         % akkaVersion,
-  "com.typesafe.akka"        %% "akka-testkit"       % akkaVersion % Test,
-  "com.novocode"             % "junit-interface"     % "0.11"      % Test
-).map(_.withDottyCompat(scalaVersion.value))
-testSuite := "actorbintree.BinaryTreeSuite"
+libraryDependencies += "com.novocode" % "junit-interface" % "0.11" % Test
+
+testOptions in Test += Tests.Argument(TestFrameworks.JUnit, "-a", "-v", "-s")
+testSuite := "lockfree.SortedListSuite"

src/main/scala/actorbintree/BinaryTreeSet.scala

@@ -1,189 +0,0 @@
-/**
- * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
- */
-package actorbintree
-
-import akka.actor._
-import scala.collection.immutable.Queue
-
-object BinaryTreeSet {
-
-  trait Operation {
-    def requester: ActorRef
-    def id: Int
-    def elem: Int
-  }
-
-  trait OperationReply {
-    def id: Int
-  }
-
-  /** Request with identifier `id` to insert an element `elem` into the tree.
-    * The actor at reference `requester` should be notified when this operation
-    * is completed.
-    */
-  case class Insert(requester: ActorRef, id: Int, elem: Int) extends Operation
-
-  /** Request with identifier `id` to check whether an element `elem` is present
-    * in the tree. The actor at reference `requester` should be notified when
-    * this operation is completed.
-    */
-  case class Contains(requester: ActorRef, id: Int, elem: Int) extends Operation
-
-  /** Request with identifier `id` to remove the element `elem` from the tree.
-    * The actor at reference `requester` should be notified when this operation
-    * is completed.
-    */
-  case class Remove(requester: ActorRef, id: Int, elem: Int) extends Operation
-
-  /** Request to perform garbage collection */
-  case object GC
-
-  /** Holds the answer to the Contains request with identifier `id`.
-    * `result` is true if and only if the element is present in the tree.
-    */
-  case class ContainsResult(id: Int, result: Boolean) extends OperationReply
-
-  /** Message to signal successful completion of an insert or remove operation. */
-  case class OperationFinished(id: Int) extends OperationReply
-
-}
-
-
-class BinaryTreeSet extends Actor {
-  import BinaryTreeSet._
-  import BinaryTreeNode._
-
-  def createRoot: ActorRef = context.actorOf(BinaryTreeNode.props(0, initiallyRemoved = true))
-
-  var root = createRoot
-
-  // optional
-  var pendingQueue = Queue.empty[Operation]
-
-  // optional
-  def receive = normal
-
-  // optional
-  /** Accepts `Operation` and `GC` messages. */
-  val normal: Receive = {
-    case op:Operation => root ! op
-    case GC => {
-      val newRoot = createRoot;
-      root ! CopyTo(newRoot)
-      context.become(garbageCollecting(newRoot))
-    }
-   }
-
-  // optional
-  /** Handles messages while garbage collection is performed.
-    * `newRoot` is the root of the new binary tree where we want to copy
-    * all non-removed elements into.
-    */
-  def garbageCollecting(newRoot: ActorRef): Receive = {
-    case op:Operation => pendingQueue = pendingQueue.enqueue(op)
-    case CopyFinished =>
-      pendingQueue.foreach(newRoot ! _) //foreach preserves order of a queue (same as dequeueing)
-      root ! PoisonPill //Will also stop all of its children
-      pendingQueue = Queue.empty
-      root = newRoot;
-      context.become(normal)
-    //Ignore GC messages here
-  }
-}
-
-object BinaryTreeNode {
-  trait Position
-
-  case object Left extends Position
-  case object Right extends Position
-
-  case class CopyTo(treeNode: ActorRef)
-  case object CopyFinished
-
-  def props(elem: Int, initiallyRemoved: Boolean) = Props(classOf[BinaryTreeNode],  elem, initiallyRemoved)
-}
-
-class BinaryTreeNode(val elem: Int, initiallyRemoved: Boolean) extends Actor {
-  import BinaryTreeNode._
-  import BinaryTreeSet._
-
-  var subtrees = Map[Position, ActorRef]()
-  var removed = initiallyRemoved
-
-  // optional
-  def receive = normal
-
-  def goDownTo(elem : Int) : Position = if(elem < this.elem) Left else Right
-  // optional
-  /** Handles `Operation` messages and `CopyTo` requests. */
-  val normal: Receive = {
-    case Insert  (requester, id, elem) =>
-      if(elem == this.elem && !removed){
-        requester ! OperationFinished(id)
-      }else{
-        val nextPos = goDownTo(elem)
-        
-        subtrees get nextPos match{
-          case Some(node) => node ! Insert(requester, id, elem)
-          case None => {
-              val newActorSubtree = (nextPos, context.actorOf(BinaryTreeNode.props(elem, false)))
-              subtrees = subtrees + newActorSubtree
-              requester ! OperationFinished(id);
-          }
-        }
-      }
-    case Contains(requester, id, elem) =>
-      if(elem == this.elem && !removed)
-        requester ! ContainsResult(id, true)
-      else{
-        //Need to search subtrees
-        subtrees get goDownTo(elem) match{
-          case Some(node) => node ! Contains(requester, id, elem)
-          case None => requester ! ContainsResult(id, false)
-        }
-      }
-        
-    case Remove  (requester, id, elem) => 
-      if(elem == this.elem && !removed){
-        removed = true
-        requester ! OperationFinished(id)
-      }else{
-        subtrees get goDownTo(elem) match{
-          case Some(node) => node ! Remove(requester, id, elem)
-          case None => requester ! OperationFinished(id) // (elem isn't in the tree)
-        }
-      }
-
-    case CopyTo(newRoot) =>
-      //We are already done, nothing to do
-      if(removed && subtrees.isEmpty) context.parent ! CopyFinished
-      else{
-        if(!removed) newRoot ! Insert(self, elem, elem)
-        subtrees.values foreach(_ ! CopyTo(newRoot)) //Copy subtrees elems
-        //val insertConfirmed = if(removed) true else false, hence we can simply pass removed
-        context.become(copying(subtrees.values.toSet, removed))
-      }
-  }
-
-  // optional
-  /** `expected` is the set of ActorRefs whose replies we are waiting for,
-    * `insertConfirmed` tracks whether the copy of this node to the new tree has been confirmed.
-    */
-  def copying(expected: Set[ActorRef], insertConfirmed: Boolean): Receive = {
-    //To catch the insert of this node into the new tree beeing finished
-    case OperationFinished(_) => {
-      if(expected.isEmpty) context.parent ! CopyFinished
-      else context.become(copying(expected, true))
-    }
-    
-    case CopyFinished => {
-      val newExp = expected-sender
-      if(insertConfirmed && newExp.isEmpty){
-        context.parent ! CopyFinished
-      }else{
-        context.become(copying(newExp, insertConfirmed))
-      }
-    }
-  }
-}

src/main/scala/lockfree/AbstractSortedList.scala

@@ -0,0 +1,32 @@
+package lockfree
+
+import instrumentation.LockFreeMonitor
+import scala.collection._
+import java.util.concurrent.atomic._
+
+
+abstract class AbstractSortedList extends LockFreeMonitor {
+  
+  def createNode(value: Int, tail: Option[Node], isHead: Boolean = false) = new Node(value, tail) {
+    override def toString = if(isHead) "HEAD" else super.toString
+  }
+  
+  def firstNode: Option[Node] 
+  
+  def findNodeWithPrev(pred: Int => Boolean): (Node, Option[Node])
+  
+  def insert(e: Int): Unit
+  
+  def delete(e: Int): Boolean
+    
+  def toList: List[Int] = {
+    var curr = firstNode
+    var list = List[Int]()
+    while(curr.nonEmpty) {
+      if(!curr.get.deleted) list :+= curr.get.value
+      curr = curr.get.next 
+    }
+    list
+  }
+}
+

src/main/scala/lockfree/AtomicVariable.scala

@@ -0,0 +1,25 @@
+package lockfree
+
+import java.util.concurrent.atomic._
+
+abstract class AbstractAtomicVariable[T] {
+  def get: T
+  def compareAndSet(expect: T, newval: T) : Boolean
+}
+
+class AtomicVariable[T](initial: T) extends AbstractAtomicVariable[T] {
+
+  private val atomic = new AtomicReference[T](initial)
+
+  override def get: T = atomic.get()
+
+  override def compareAndSet(expected: T, value: T): Boolean = {
+    val current = atomic.get
+    if (current == expected) {
+      atomic.compareAndSet(current, value)
+    }
+    else {
+      false
+    }
+  }
+}

src/main/scala/lockfree/Node.scala

@@ -0,0 +1,23 @@
+ 
+package lockfree
+
+abstract class Node(val value: Int, initTail: Option[Node]) {
+
+  // The type of mutable state held by node.
+  type State = (Option[Node], Boolean) //Boolean flag indicates whether THIS has been deleted or not !! not next
+
+  // The initial mutable state of the node.
+  def initialState: State = (initTail, false);
+
+  // The atomic variable that holds the state.
+  val atomicState: AbstractAtomicVariable[State] = new AtomicVariable[State](initialState)
+
+  // Function to read the next node from the state.
+  def next: Option[Node] = atomicState.get._1
+
+  // Should return true if the node was marked as deleted.
+  def deleted: Boolean = atomicState.get._2
+
+  // Should mark the node as deleted.
+  def mark: Boolean = atomicState.compareAndSet((next, false), (next, true))
+}

src/main/scala/lockfree/SortedList.scala

@@ -0,0 +1,54 @@
+package lockfree
+
+import scala.annotation.tailrec
+
+class SortedList extends AbstractSortedList {
+
+  // The sentinel node at the head.
+  private val _head: Node = createNode(0, None, isHead = true)
+
+  // The first logical node is referenced by the head.
+  def firstNode: Option[Node] = _head.next
+
+  // Finds the first node whose value satisfies the predicate.
+  // Returns the predecessor of the node and the node.
+  def findNodeWithPrev(pred: Int => Boolean): (Node, Option[Node]) = {
+    def findRec(prev : Node, curr : Option[Node]) : (Node, Option[Node]) = {
+      (prev, curr) match {
+        case (last, None) => (last, None);
+        case (_, Some(node)) =>
+          if(node.deleted) {
+            prev.atomicState.compareAndSet((curr, false), (node.next, false))
+            findNodeWithPrev(pred)
+          }else if(pred(node.value)) (prev, curr)
+          else findRec(node, node.next)
+      }
+    }
+    findRec(_head, _head.next)
+  }
+
+  // Insert an element in the list.
+  def insert(e: Int): Unit = {
+    val (pred, next) = findNodeWithPrev(_ >= e);
+    val n = createNode(e, next)
+    if(!pred.atomicState.compareAndSet((next, false), (Some(n), false))) insert(e)
+  }
+
+  // Checks if the list contains an element.
+  def contains(e: Int): Boolean = {
+    findNodeWithPrev(_ == e)._2 match {
+      case None => false
+      case _ => true;
+    }
+  }
+
+  // Delete an element from the list.
+  // Should only delete one element when multiple occurences are present.
+  def delete(e: Int): Boolean = {
+    val (pred, next) = findNodeWithPrev(_ == e)
+    next match{
+      case None => false
+      case Some(x) => if(x.mark) true else delete(e)
+    }
+  }
+}

src/main/scala/lockfree/SortingBenchmarks.scala

@@ -0,0 +1,83 @@
+package lockfree
+
+import scala.util.Random
+import instrumentation.Stats._
+
+object SortingBenchmarks extends App {
+
+  val items = 2500
+  val threads = 12
+
+  val insertions = List.fill(items)(Random.nextInt)
+  val deletions = Random.shuffle(insertions)
+  val parInsertions = parBuckets(threads, insertions)_
+  val parDeletions = parBuckets(threads, deletions)_
+
+  private class SynchronizedSortedList extends SortedList {
+    val lock = new Object
+    def syncTraverse(stop: Int => Boolean) = lock.synchronized(super.findNodeWithPrev(stop))
+    def syncInsert(e: Int) = lock.synchronized(super.insert(e))
+    def syncDelete(e: Int) = lock.synchronized(super.delete(e))
+  }
+
+  val syncSeqTime = {
+    val l = new SynchronizedSortedList
+    withTime {
+      insertions.foreach(l.syncInsert)
+      deletions.foreach(l.syncDelete)
+    }._2
+  }
+
+  val syncParTime = {
+    val l = new SynchronizedSortedList
+    withTime {
+      val ops = parInsertions(l.syncInsert) ++ parDeletions(l.syncDelete)
+      ops.foreach(_.start)
+      ops.foreach(_.join)
+    }._2
+  }
+
+  val fineSeqTime = {
+    val l = new SortedList
+    withTime {
+      insertions.foreach(l.insert)
+      deletions.foreach(l.delete)
+    }._2
+  }
+
+  val fineParTime = {
+    val l = new SortedList
+    withTime {
+      val ops = parInsertions(l.insert) ++ parDeletions(l.delete)
+      ops.foreach(_.start)
+      ops.foreach(_.join)
+    }._2
+  }
+
+  println(
+    s"""
+      |***** Results *****
+      |
+      |synchronized:
+      |  - sequential:  $syncSeqTime
+      |  - parallel:    $syncParTime
+      |  - speedup:     ${syncSeqTime.toFloat / syncParTime}
+      |
+      |fine-grained:
+      |  - sequential:  $fineSeqTime
+      |  - parallel:    $fineParTime
+      |  - speedup:     ${fineSeqTime.toFloat / fineParTime}
+      |
+      |synchronized/fine-grained:
+      |  - speedup:     ${syncParTime.toFloat / fineParTime}
+      |
+    """.stripMargin)
+
+  def parBuckets(threadCount: Int, items: List[Int])(op: Int => Any): List[Thread] =
+    items.grouped(items.size / threadCount).toList.map { bucket =>
+      new Thread {
+        override def run(): Unit =
+          bucket.foreach(op)
+      }
+    }
+}

src/main/scala/lockfree/instrumentation/MockedMonitor.scala

@@ -0,0 +1,72 @@
+package lockfree.instrumentation
+
+trait MockedMonitor extends Monitor {
+  def scheduler: Scheduler
+  
+  // Can be overriden.
+  override def waitDefault() = {
+    scheduler.log("wait")
+    scheduler updateThreadState Wait(this, scheduler.threadLocks.tail)
+  }
+  override def synchronizedDefault[T](toExecute: =>T): T = {
+    scheduler.log("synchronized check") 
+    val prevLocks = scheduler.threadLocks
+    scheduler updateThreadState Sync(this, prevLocks) // If this belongs to prevLocks, should just continue.
+    scheduler.log("synchronized -> enter")
+    try {
+      toExecute
+    } finally {
+      scheduler updateThreadState Running(prevLocks)
+      scheduler.log("synchronized -> out")
+    }    
+  }
+  override def notifyDefault() = {
+    scheduler mapOtherStates {
+      state => state match {
+        case Wait(lockToAquire, locks) if lockToAquire == this => SyncUnique(this, state.locks)
+        case e => e
+      }
+    }
+    scheduler.log("notify")
+  }
+  override def notifyAllDefault() = {
+    scheduler mapOtherStates {
+      state => state match {
+        case Wait(lockToAquire, locks) if lockToAquire == this => Sync(this, state.locks)
+        case SyncUnique(lockToAquire, locks) if lockToAquire == this => Sync(this, state.locks)
+        case e => e
+      }
+    }
+    scheduler.log("notifyAll")
+  }
+}
+
+trait LockFreeMonitor extends Monitor {
+  override def waitDefault() = {
+    throw new Exception("Please use lock-free structures and do not use wait()")
+  }
+  override def synchronizedDefault[T](toExecute: =>T): T = {
+    throw new Exception("Please use lock-free structures and do not use synchronized()")
+  }
+  override def notifyDefault() = {
+    throw new Exception("Please use lock-free structures and do not use notify()")
+  }
+  override def notifyAllDefault() = {
+    throw new Exception("Please use lock-free structures and do not use notifyAll()")
+  }
+}
+
+
+abstract class ThreadState {
+  def locks: Seq[AnyRef]
+}
+trait CanContinueIfAcquiresLock extends ThreadState {
+  def lockToAquire: AnyRef
+}
+case object Start extends ThreadState { def locks: Seq[AnyRef] = Seq.empty }
+case object End extends ThreadState { def locks: Seq[AnyRef] = Seq.empty }
+case class Wait(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState
+case class SyncUnique(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState with CanContinueIfAcquiresLock
+case class Sync(lockToAquire: AnyRef, locks: Seq[AnyRef]) extends ThreadState with CanContinueIfAcquiresLock
+case class Running(locks: Seq[AnyRef]) extends ThreadState
+case class VariableReadWrite(locks: Seq[AnyRef]) extends ThreadState

src/main/scala/lockfree/instrumentation/Monitor.scala

@@ -0,0 +1,23 @@
+package lockfree.instrumentation
+
+class Dummy
+
+trait Monitor {
+  implicit val dummy: Dummy = new Dummy
+
+  def wait()(implicit i: Dummy) = waitDefault()
+
+  def synchronized[T](e: => T)(implicit i: Dummy) = synchronizedDefault(e)
+
+  def notify()(implicit i: Dummy) = notifyDefault()
+
+  def notifyAll()(implicit i: Dummy) = notifyAllDefault()
+
+  private val lock = new AnyRef
+
+  // Can be overriden.
+  def waitDefault(): Unit = lock.wait()
+  def synchronizedDefault[T](toExecute: =>T): T = lock.synchronized(toExecute)
+  def notifyDefault(): Unit = lock.notify()
+  def notifyAllDefault(): Unit = lock.notifyAll()
+}

src/main/scala/lockfree/instrumentation/SchedulableSortedList.scala

@@ -0,0 +1,35 @@
+package lockfree.instrumentation
+
+import scala.annotation.tailrec
+import lockfree._
+import java.util.concurrent.atomic._
+
+class SchedulableAtomicVariable[T](initial: T, scheduler: Scheduler, self: Node) extends AbstractAtomicVariable[T] {
+  private val proxied: AtomicVariable[T] = new AtomicVariable[T](initial)
+
+  override def get: T = scheduler.exec {
+    proxied.get
+  } ( s"", Some(res => s"$self: get $res") )
+
+  override def compareAndSet(expect: T, newval: T): Boolean = {
+    scheduler.exec {
+      proxied.compareAndSet(expect, newval)
+    } (s"$self: compareAndSet expect = $expect, newval = $newval", Some(res => s"$self: Did it set? $res") )
+  }
+}
+
+class SchedulableNode(value: Int, initTail: Option[Node], val scheduler: Scheduler) extends Node(value, initTail) with LockFreeMonitor { self =>
+
+  override val atomicState: AbstractAtomicVariable[State] = new SchedulableAtomicVariable[State](initialState, scheduler, this)
+
+  override def toString: String =
+    String.format("Node(%s)#%02d", value.toString, new Integer(## % 100))
+}
+
+class SchedulableSortedList(val scheduler: Scheduler) extends SortedList with LockFreeMonitor {
+
+  override def createNode(value: Int, tail: Option[Node], isHead: Boolean) = new SchedulableNode(value, tail, scheduler) {
+    override def toString = if(isHead) "HEAD" else super.toString
+  }
+}
+

src/main/scala/lockfree/instrumentation/Scheduler.scala

@@ -0,0 +1,304 @@
+package lockfree.instrumentation
+
+import java.util.concurrent._;
+import scala.concurrent.duration._
+import scala.collection.mutable._
+import Stats._
+
+import java.util.concurrent.atomic.AtomicInteger
+
+sealed abstract class Result
+case class RetVal(rets: List[Any]) extends Result
+case class Except(msg: String, stackTrace: Array[StackTraceElement]) extends Result
+case class Timeout(msg: String) extends Result
+
+/**
+ * A class that maintains schedule and a set of thread ids.
+ * The schedules are advanced after an operation of a SchedulableBuffer is performed.
+ * Note: the real schedule that is executed may deviate from the input schedule
+ * due to the adjustments that had to be made for locks
+ */
+class Scheduler(sched: List[Int]) {
+  val maxOps = 500 // a limit on the maximum number of operations the code is allowed to perform
+
+  private var schedule = sched
+  private var numThreads = 0
+  private val realToFakeThreadId = Map[Long, Int]()
+  private val opLog = ListBuffer[String]() // a mutable list (used for efficient concat)
+  private val threadStates = Map[Int, ThreadState]()
+
+  /**
+   * Runs a set of operations in parallel as per the schedule.
+   * Each operation may consist of many primitive operations like reads or writes
+   * to shared data structure each of which should be executed using the function `exec`.
+   * @timeout in milliseconds
+   * @return true - all threads completed on time,  false -some tests timed out.
+   */
+  def runInParallel(timeout: Long, ops: List[() => Any]): Result = {
+    numThreads = ops.length
+    val threadRes = Array.fill(numThreads) { None: Any }
+    var exception: Option[Except] = None
+    val syncObject = new Object()
+    var completed = new AtomicInteger(0)
+    // create threads
+    val threads = ops.zipWithIndex.map {
+      case (op, i) =>
+        new Thread(new Runnable() {
+          def run(): Unit = {
+            val fakeId = i + 1
+            setThreadId(fakeId)
+            try {
+              updateThreadState(Start)
+              val res = op()
+              updateThreadState(End)
+              threadRes(i) = res
+              // notify the master thread if all threads have completed
+              if (completed.incrementAndGet() == ops.length) {
+                syncObject.synchronized { syncObject.notifyAll() }
+              }
+            } catch {
+              case e: Throwable if exception != None => // do nothing here and silently fail
+              case e: Throwable =>
+                log(s"throw ${e.toString}")
+                exception = Some(Except(s"Thread $fakeId crashed on the following schedule: \n" + opLog.mkString("\n"),
+                    e.getStackTrace))
+                syncObject.synchronized { syncObject.notifyAll() }
+              //println(s"$fakeId: ${e.toString}")
+              //Runtime.getRuntime().halt(0) //exit the JVM and all running threads (no other way to kill other threads)
+            }
+          }
+        })
+    }
+    // start all threads
+    threads.foreach(_.start())
+    // wait for all threads to complete, or for an exception to be thrown, or for the time out to expire
+    var remTime = timeout
+    syncObject.synchronized {
+      timed { if(completed.get() != ops.length) syncObject.wait(timeout) } { time => remTime -= time }
+    }
+    if (exception.isDefined) {
+      exception.get
+    } else if (remTime <= 1) { // timeout ? using 1 instead of zero to allow for some errors
+      Timeout(opLog.mkString("\n"))
+    } else {
+      // every thing executed normally
+      RetVal(threadRes.toList)
+    }
+  }
+
+  // Updates the state of the current thread
+  def updateThreadState(state: ThreadState): Unit = {
+    val tid = threadId
+    synchronized {
+      threadStates(tid) = state
+    }
+    state match {
+      case Sync(lockToAquire, locks) =>
+        if (locks.indexOf(lockToAquire) < 0) waitForTurn else {
+          // Re-aqcuiring the same lock
+          updateThreadState(Running(lockToAquire +: locks))
+        }
+      case Start      => waitStart()
+      case End        => removeFromSchedule(tid)
+      case Running(_) =>
+      case _          => waitForTurn // Wait, SyncUnique, VariableReadWrite
+    }
+  }
+
+  def waitStart(): Unit = {
+    //while (threadStates.size < numThreads) {
+    //Thread.sleep(1)
+    //}
+    synchronized {
+      if (threadStates.size < numThreads) {
+        wait()
+      } else {
+        notifyAll()
+      }
+    }
+  }
+
+  def threadLocks = {
+    synchronized {
+      threadStates(threadId).locks
+    }
+  }
+
+  def threadState = {
+    synchronized {
+      threadStates(threadId)
+    }
+  }
+
+  def mapOtherStates(f: ThreadState => ThreadState) = {
+    val exception = threadId
+    synchronized {
+      for (k <- threadStates.keys if k != exception) {
+        threadStates(k) = f(threadStates(k))
+      }
+    }
+  }
+
+  def log(str: String) = {
+    if((realToFakeThreadId contains Thread.currentThread().getId())) {
+      val space = (" " * ((threadId - 1) * 2))
+      val s = space + threadId + ":" + "\n".r.replaceAllIn(str, "\n" + space + "  ")
+      opLog += s
+    }
+  }
+
+  /**
+   * Executes a read or write operation to a global data structure as per the given schedule
+   * @param msg a message corresponding to the operation that will be logged
+   */
+  def exec[T](primop: => T)(msg: => String, postMsg: => Option[T => String] = None): T = {
+    if(! (realToFakeThreadId contains Thread.currentThread().getId())) {
+      primop
+    } else {
+      updateThreadState(VariableReadWrite(threadLocks))
+      val m = msg
+      if(m != "") log(m)
+      if (opLog.size > maxOps)
+        throw new Exception(s"Total number of reads/writes performed by threads exceed $maxOps. A possible deadlock!")
+      val res = primop
+      postMsg match {
+        case Some(m) => log(m(res))
+        case None =>
+      }
+      res
+    }
+  }
+
+  private def setThreadId(fakeId: Int) = synchronized {
+    realToFakeThreadId(Thread.currentThread.getId) = fakeId
+  }
+
+  def threadId =
+    try {
+      realToFakeThreadId(Thread.currentThread().getId())
+    } catch {
+    case e: NoSuchElementException =>
+      throw new Exception("You are accessing shared variables in the constructor. This is not allowed. The variables are already initialized!")
+    }
+
+  private def isTurn(tid: Int) = synchronized {
+    (!schedule.isEmpty && schedule.head != tid)
+  }
+
+  def canProceed(): Boolean = {
+    val tid = threadId
+    canContinue match {
+      case Some((i, state)) if i == tid =>
+        //println(s"$tid: Runs ! Was in state $state")
+        canContinue = None
+        state match {
+          case Sync(lockToAquire, locks) => updateThreadState(Running(lockToAquire +: locks))
+          case SyncUnique(lockToAquire, locks) =>
+            mapOtherStates {
+              _ match {
+                case SyncUnique(lockToAquire2, locks2) if lockToAquire2 == lockToAquire => Wait(lockToAquire2, locks2)
+                case e => e
+              }
+            }
+            updateThreadState(Running(lockToAquire +: locks))
+          case VariableReadWrite(locks) => updateThreadState(Running(locks))
+        }
+        true
+      case Some((i, state)) =>
+        //println(s"$tid: not my turn but $i !")
+        false
+      case None =>
+        false
+    }
+  }
+
+  var threadPreference = 0 // In the case the schedule is over, which thread should have the preference to execute.
+
+  /** returns true if the thread can continue to execute, and false otherwise */
+  def decide(): Option[(Int, ThreadState)] = {
+    if (!threadStates.isEmpty) { // The last thread who enters the decision loop takes the decision.
+      //println(s"$threadId: I'm taking a decision")
+      if (threadStates.values.forall { case e: Wait => true case _ => false }) {
+        val waiting = threadStates.keys.map(_.toString).mkString(", ")
+        val s = if (threadStates.size > 1) "s" else ""
+        val are = if (threadStates.size > 1) "are" else "is"
+        throw new Exception(s"Deadlock: Thread$s $waiting $are waiting but all others have ended and cannot notify them.")
+      } else {
+        // Threads can be in Wait, Sync, SyncUnique, and VariableReadWrite mode.
+        // Let's determine which ones can continue.
+        val notFree = threadStates.collect { case (id, state) => state.locks }.flatten.toSet
+        val threadsNotBlocked = threadStates.toSeq.filter {
+          case (id, v: VariableReadWrite)         => true
+          case (id, v: CanContinueIfAcquiresLock) => !notFree(v.lockToAquire) || (v.locks contains v.lockToAquire)
+          case _                                  => false
+        }
+        if (threadsNotBlocked.isEmpty) {
+          val waiting = threadStates.keys.map(_.toString).mkString(", ")
+          val s = if (threadStates.size > 1) "s" else ""
+          val are = if (threadStates.size > 1) "are" else "is"
+          val whoHasLock = threadStates.toSeq.flatMap { case (id, state) => state.locks.map(lock => (lock, id)) }.toMap
+          val reason = threadStates.collect {
+            case (id, state: CanContinueIfAcquiresLock) if !notFree(state.lockToAquire) =>
+              s"Thread $id is waiting on lock ${state.lockToAquire} held by thread ${whoHasLock(state.lockToAquire)}"
+          }.mkString("\n")
+          throw new Exception(s"Deadlock: Thread$s $waiting are interlocked. Indeed:\n$reason")
+        } else if (threadsNotBlocked.size == 1) { // Do not consume the schedule if only one thread can execute.
+          Some(threadsNotBlocked(0))
+        } else {
+          val next = schedule.indexWhere(t => threadsNotBlocked.exists { case (id, state) => id == t })
+          if (next != -1) {
+            //println(s"$threadId: schedule is $schedule, next chosen is ${schedule(next)}")
+            val chosenOne = schedule(next) // TODO: Make schedule a mutable list.
+            schedule = schedule.take(next) ++ schedule.drop(next + 1)
+            Some((chosenOne, threadStates(chosenOne)))
+          } else {
+            threadPreference = (threadPreference + 1) % threadsNotBlocked.size
+            val chosenOne = threadsNotBlocked(threadPreference) // Maybe another strategy
+            Some(chosenOne)
+            //threadsNotBlocked.indexOf(threadId) >= 0
+            /*
+            val tnb = threadsNotBlocked.map(_._1).mkString(",")
+            val s = if (schedule.isEmpty) "empty" else schedule.mkString(",")
+            val only = if (schedule.isEmpty) "" else " only"
+            throw new Exception(s"The schedule is $s but$only threads ${tnb} can continue")*/
+          }
+        }
+      }
+    } else canContinue
+  }
+
+  /**
+   * This will be called before a schedulable operation begins.
+   * This should not use synchronized
+   */
+  var numThreadsWaiting = new AtomicInteger(0)
+  //var waitingForDecision = Map[Int, Option[Int]]() // Mapping from thread ids to a number indicating who is going to make the choice.
+  var canContinue: Option[(Int, ThreadState)] = None // The result of the decision thread Id of the thread authorized to continue.
+  private def waitForTurn = {
+    synchronized {
+      if (numThreadsWaiting.incrementAndGet() == threadStates.size) {
+        canContinue = decide()
+        notifyAll()
+      }
+      //waitingForDecision(threadId) = Some(numThreadsWaiting)
+      //println(s"$threadId Entering waiting with ticket number $numThreadsWaiting/${waitingForDecision.size}")
+      while (!canProceed()) wait()
+    }
+    numThreadsWaiting.decrementAndGet()
+  }
+
+  /**
+   * To be invoked when a thread is about to complete
+   */
+  private def removeFromSchedule(fakeid: Int) = synchronized {
+    //println(s"$fakeid: I'm taking a decision because I finished")
+    schedule = schedule.filterNot(_ == fakeid)
+    threadStates -= fakeid
+    if (numThreadsWaiting.get() == threadStates.size) {
+      canContinue = decide()
+      notifyAll()
+    }
+  }
+
+  def getOperationLog() = opLog
+}

src/main/scala/lockfree/instrumentation/Stats.scala

@@ -0,0 +1,23 @@
+/* Copyright 2009-2015 EPFL, Lausanne */
+package lockfree.instrumentation
+
+import java.lang.management._
+
+/**
+ * A collection of methods that can be used to collect run-time statistics about Leon programs.
+ * This is mostly used to test the resources properties of Leon programs
+ */
+object Stats {
+  def timed[T](code: => T)(cont: Long => Unit): T = {
+    var t1 = System.currentTimeMillis()
+    val r = code
+    cont((System.currentTimeMillis() - t1))
+    r
+  }
+
+  def withTime[T](code: => T): (T, Long) = {
+    var t1 = System.currentTimeMillis()
+    val r = code
+    (r, (System.currentTimeMillis() - t1))
+  }
+}

src/main/scala/lockfree/instrumentation/TestHelper.scala

@@ -0,0 +1,124 @@
+package lockfree.instrumentation
+
+import scala.util.Random
+import scala.collection.mutable.{Map => MutableMap}
+
+import Stats._
+
+object TestHelper {
+  val noOfSchedules = 10000 // set this to 100k during deployment
+  val readWritesPerThread = 20 // maximum number of read/writes possible in one thread
+  val contextSwitchBound = 10
+  val testTimeout = 240 // the total time out for a test in seconds
+  val schedTimeout = 15 // the total time out for execution of a schedule in secs
+
+  // Helpers
+  /*def testManySchedules(op1: => Any): Unit = testManySchedules(List(() => op1))
+  def testManySchedules(op1: => Any, op2: => Any): Unit = testManySchedules(List(() => op1, () => op2))
+  def testManySchedules(op1: => Any, op2: => Any, op3: => Any): Unit = testManySchedules(List(() => op1, () => op2, () => op3))
+  def testManySchedules(op1: => Any, op2: => Any, op3: => Any, op4: => Any): Unit = testManySchedules(List(() => op1, () => op2, () => op3, () => op4))*/
+
+  def testSequential[T](ops: Scheduler => Any)(assertions: T => (Boolean, String)) =
+    testManySchedules(1,
+      (sched: Scheduler) => {
+        (List(() => ops(sched)),
+         (res: List[Any]) => assertions(res.head.asInstanceOf[T]))
+      })
+
+  /**
+   * @numThreads number of threads
+   * @ops operations to be executed, one per thread
+   * @assertion as condition that will executed after all threads have completed (without exceptions)
+   * 					 the arguments are the results of the threads
+   */
+  def testManySchedules(numThreads: Int,
+      ops: Scheduler =>
+        (List[() => Any], // Threads
+         List[Any] => (Boolean, String)) // Assertion
+      ) = {
+    var timeout = testTimeout * 1000L
+    val threadIds = (1 to numThreads)
+    //(1 to scheduleLength).flatMap(_ => threadIds).toList.permutations.take(noOfSchedules).foreach {
+    val schedules = (new ScheduleGenerator(numThreads)).schedules()
+    var schedsExplored = 0
+    schedules.takeWhile(_ => schedsExplored <= noOfSchedules && timeout > 0).foreach {
+      //case _ if timeout <= 0 => // break
+      case schedule =>
+        schedsExplored += 1
+        val schedr = new Scheduler(schedule)
+        //println("Exploring Sched: "+schedule)
+        val (threadOps, assertion) = ops(schedr)
+        if (threadOps.size != numThreads)
+          throw new IllegalStateException(s"Number of threads: $numThreads, do not match operations of threads: $threadOps")
+        timed { schedr.runInParallel(schedTimeout * 1000, threadOps) } { t => timeout -= t } match {
+          case Timeout(msg) =>
+            throw new java.lang.AssertionError("assertion failed\n"+"The schedule took too long to complete. A possible deadlock! \n"+msg)
+          case Except(msg, stkTrace) =>
+            val traceStr = "Thread Stack trace: \n"+stkTrace.map(" at "+_.toString).mkString("\n")
+            throw new java.lang.AssertionError("assertion failed\n"+msg+"\n"+traceStr)
+          case RetVal(threadRes) =>
+            // check the assertion
+            val (success, custom_msg) = assertion(threadRes)
+            if (!success) {
+              val msg = "The following schedule resulted in wrong results: \n" + custom_msg + "\n" + schedr.getOperationLog().mkString("\n")
+              throw new java.lang.AssertionError("Assertion failed: "+msg)
+            }
+        }
+    }
+    if (timeout <= 0) {
+      throw new java.lang.AssertionError("Test took too long to complete! Cannot check all schedules as your code is too slow!")
+    }
+  }
+
+  /**
+   * A schedule generator that is based on the context bound
+   */
+  class ScheduleGenerator(numThreads: Int) {
+    val scheduleLength = readWritesPerThread * numThreads
+    val rands = (1 to scheduleLength).map(i => new Random(0xcafe * i)) // random numbers for choosing a thread at each position
+    def schedules(): LazyList[List[Int]] = {
+      var contextSwitches = 0
+      var contexts = List[Int]() // a stack of thread ids in the order of context-switches
+      val remainingOps = MutableMap[Int, Int]()
+      remainingOps ++= (1 to numThreads).map(i => (i, readWritesPerThread)) // num ops remaining in each thread
+      val liveThreads = (1 to numThreads).toSeq.toBuffer
+
+      /**
+       * Updates remainingOps and liveThreads once a thread is chosen for a position in the schedule
+       */
+      def updateState(tid: Int): Unit = {
+        val remOps = remainingOps(tid)
+        if (remOps == 0) {
+          liveThreads -= tid
+        } else {
+          remainingOps += (tid -> (remOps - 1))
+        }
+      }
+      val schedule = rands.foldLeft(List[Int]()) {
+        case (acc, r) if contextSwitches < contextSwitchBound =>
+          val tid = liveThreads(r.nextInt(liveThreads.size))
+          contexts match {
+            case prev :: tail if prev != tid => // we have a new context switch here
+              contexts +:= tid
+              contextSwitches += 1
+            case prev :: tail =>
+            case _ => // init case
+              contexts +:= tid
+          }
+          updateState(tid)
+          acc :+ tid
+        case (acc, _) => // here context-bound has been reached so complete the schedule without any more context switches
+          if (!contexts.isEmpty) {
+            contexts = contexts.dropWhile(remainingOps(_) == 0)
+          }
+          val tid = contexts match {
+            case top :: tail => top
+            case _ => liveThreads(0)  // here, there has to be threads that have not even started
+          }
+          updateState(tid)
+          acc :+ tid
+      }
+      schedule #:: schedules()
+    }
+  }
+}

src/main/scala/lockfree/instrumentation/TestUtils.scala

@@ -0,0 +1,19 @@
+package lockfree.instrumentation
+
+import scala.concurrent._
+import scala.concurrent.duration._
+import scala.concurrent.ExecutionContext.Implicits.global
+
+object TestUtils {
+  def failsOrTimesOut[T](action: => T): Boolean = {
+    val asyncAction = Future {
+      action
+    }
+    try {
+      Await.result(asyncAction, 2000.millisecond)
+    } catch {
+      case _: Throwable => return true
+    }
+    return false
+  }
+}

src/test/scala/actorbintree/BinaryTreeSuite.scala

@@ -1,126 +0,0 @@
-/**
- * Copyright (C) 2009-2015 Typesafe Inc. <http://www.typesafe.com>
- */
-package actorbintree
-
-import akka.actor.{ActorRef, ActorSystem, Props, actorRef2Scala, scala2ActorRef}
-import akka.testkit.{ImplicitSender, TestKit, TestProbe}
-import org.junit.Test
-import org.junit.Assert._
-
-import scala.util.Random
-import scala.concurrent.duration._
-
-class BinaryTreeSuite extends TestKit(ActorSystem("BinaryTreeSuite")) with ImplicitSender {
-
-  import actorbintree.BinaryTreeSet._
-
-  def receiveN(requester: TestProbe, ops: Seq[Operation], expectedReplies: Seq[OperationReply]): Unit =
-    requester.within(5.seconds) {
-      val repliesUnsorted = for (i <- 1 to ops.size) yield try {
-        requester.expectMsgType[OperationReply]
-      } catch {
-        case ex: Throwable if ops.size > 10 => sys.error(s"failure to receive confirmation $i/${ops.size}\n$ex")
-        case ex: Throwable                  => sys.error(s"failure to receive confirmation $i/${ops.size}\nRequests:" + ops.mkString("\n    ", "\n     ", "") + s"\n$ex")
-      }
-      val replies = repliesUnsorted.sortBy(_.id)
-      if (replies != expectedReplies) {
-        val pairs = (replies zip expectedReplies).zipWithIndex filter (x => x._1._1 != x._1._2)
-        fail("unexpected replies:" + pairs.map(x => s"at index ${x._2}: got ${x._1._1}, expected ${x._1._2}").mkString("\n    ", "\n    ", ""))
-      }
-    }
-
-  def verify(probe: TestProbe, ops: Seq[Operation], expected: Seq[OperationReply]): Unit = {
-    val topNode = system.actorOf(Props[BinaryTreeSet])
-
-    ops foreach { op =>
-      topNode ! op
-    }
-
-    receiveN(probe, ops, expected)
-    // the grader also verifies that enough actors are created
-  }
-
-  @Test def `proper inserts and lookups (5pts)`(): Unit = {
-    val topNode = system.actorOf(Props[BinaryTreeSet])
-
-    topNode ! Contains(testActor, id = 1, 1)
-    expectMsg(ContainsResult(1, false))
-
-    topNode ! Insert(testActor, id = 2, 1)
-    topNode ! Contains(testActor, id = 3, 1)
-
-    expectMsg(OperationFinished(2))
-    expectMsg(ContainsResult(3, true))
-    ()
-  }
-
-  @Test def `instruction example (5pts)`(): Unit = {
-    val requester = TestProbe()
-    val requesterRef = requester.ref
-    val ops = List(
-      Insert(requesterRef, id=100, 1),
-      Contains(requesterRef, id=50, 2),
-      Remove(requesterRef, id=10, 1),
-      Insert(requesterRef, id=20, 2),
-      Contains(requesterRef, id=80, 1),
-      Contains(requesterRef, id=70, 2)
-    )
-
-    val expectedReplies = List(
-      OperationFinished(id=10),
-      OperationFinished(id=20),
-      ContainsResult(id=50, false),
-      ContainsResult(id=70, true),
-      ContainsResult(id=80, false),
-      OperationFinished(id=100)
-    )
-
-    verify(requester, ops, expectedReplies)
-  }
-
-
-  @Test def `behave identically to built-in set (includes GC) (40pts)`(): Unit = {
-    val rnd = new Random()
-    def randomOperations(requester: ActorRef, count: Int): Seq[Operation] = {
-      def randomElement: Int = rnd.nextInt(100)
-      def randomOperation(requester: ActorRef, id: Int): Operation = rnd.nextInt(4) match {
-        case 0 => Insert(requester, id, randomElement)
-        case 1 => Insert(requester, id, randomElement)
-        case 2 => Contains(requester, id, randomElement)
-        case 3 => Remove(requester, id, randomElement)
-      }
-
-      for (seq <- 0 until count) yield randomOperation(requester, seq)
-    }
-
-    def referenceReplies(operations: Seq[Operation]): Seq[OperationReply] = {
-      var referenceSet = Set.empty[Int]
-      def replyFor(op: Operation): OperationReply = op match {
-        case Insert(_, seq, elem) =>
-          referenceSet = referenceSet + elem
-          OperationFinished(seq)
-        case Remove(_, seq, elem) =>
-          referenceSet = referenceSet - elem
-          OperationFinished(seq)
-        case Contains(_, seq, elem) =>
-          ContainsResult(seq, referenceSet(elem))
-      }
-
-      for (op <- operations) yield replyFor(op)
-    }
-
-    val requester = TestProbe()
-    val topNode = system.actorOf(Props[BinaryTreeSet])
-    val count = 1000
-
-    val ops = randomOperations(requester.ref, count)
-    val expectedReplies = referenceReplies(ops)
-
-    ops foreach { op =>
-      topNode ! op
-      if (rnd.nextDouble() < 0.1) topNode ! GC
-    }
-    receiveN(requester, ops, expectedReplies)
-  }
-}

src/test/scala/lockfree/SortedListSuite.scala

@@ -0,0 +1,96 @@
+package lockfree
+
+import scala.concurrent._
+import scala.concurrent.duration._
+import scala.collection.mutable.HashMap
+import scala.util.Random
+import org.junit._
+import org.junit.Assert.assertEquals
+import instrumentation.SchedulableSortedList
+import instrumentation.TestHelper._
+import instrumentation.TestUtils._
+
+class SortedListSuite {
+
+  @Test def `Should work when 1, 2, and 3 are inserted sequentially`: Unit = {
+    val l = new SortedList
+    l.insert(1)
+    l.insert(2)
+    l.insert(3)
+    assertEquals(List(1, 2, 3), l.toList)
+  }
+
+  @Test def `Should work when 3, 2, and 1 are inserted sequentially`: Unit = {
+    val l = new SortedList
+    l.insert(3)
+    l.insert(2)
+    l.insert(1)
+    assertEquals(List(1, 2, 3), l.toList)
+  }
+
+  @Test def `Should work when duplicate elements are inserted sequentially`: Unit = {
+    val l = new SortedList
+    l.insert(0)
+    l.insert(0)
+    l.insert(2)
+    l.insert(2)
+    assertEquals(List(0, 0, 2, 2), l.toList)
+  }
+
+  @Test def `Should return [1,4,5] when from [1,2,3,5], a thread removes 3, 2 and then inserts 4`: Unit = {
+    val l = new SortedList
+    l.insert(1)
+    l.insert(2)
+    l.insert(3)
+    l.insert(5)
+    l.delete(3)
+    l.delete(2)
+    l.insert(4)
+    assertEquals(List(1, 4, 5), l.toList)
+  }
+
+  @Test def `Should work when a random list of 100 elements are inserted sequentially`: Unit = {
+    val rand = new Random()
+    val randvals = for(i <- 1 to 100) yield rand.nextInt()
+    val l = new SortedList
+    randvals.foreach { l.insert }
+    assertEquals(randvals.sorted, l.toList)
+  }
+
+  @Test def `Should insert in parallel 1, 2 and 3 in the list (0, 4)`: Unit = {
+    testManySchedules(3, sched => {
+      val sortedList = new SchedulableSortedList(sched)
+      sortedList.insert(0)
+      sortedList.insert(4)
+      ((for(i <- 1 to 3) yield () => sortedList.insert(i)).toList,
+       results => {
+        val res = sortedList.toList
+        (res == List(0, 1, 2, 3, 4),
+        s"expected List(0, 1, 2, 3, 4), got $res")
+      })
+    })
+  }
+
+   @Test def `Should return List(true, false) when the first thread deletes 2 and the sec`: Unit = {
+    testManySchedules(2, sched => {
+      val sortedList = new SchedulableSortedList(sched)
+      sortedList.insert(1)
+      sortedList.insert(2)
+      sortedList.insert(3)
+      (List(() => sortedList.delete(2),
+            () => sortedList.delete(4)),
+      results => {
+        val res = sortedList.toList
+        val expected = List(1, 3)
+        if(res != expected) {
+           (false, s"expected the final list to be $expected, your 'delete' implementation returned ${res}")
+        } else if(results != List(true, false)) {
+          (false, s"expected threads to return List(true, false), your 'delete' implementation returned ${results}")
+        } else (true, "")
+      })
+    })
+  }
+
+
+  @Rule def individualTestTimeout = new org.junit.rules.Timeout(200 * 1000)
+}