src/test/scala/midterm22/Part6Test.scala

+package midterm22
+
+import org.junit.*
+import org.junit.Assert.*
+import instrumentation.*
+
+class Part6Test:
+  @Test(expected = classOf[AssertionError])
+  def testQuestion21() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val ticketsManager = ScheduledTicketsManager(1, scheduler)
+
+        (
+          List(
+            () =>
+              // Thread 1
+              ticketsManager.getTicket(),
+            () =>
+              // Thread 2
+              ticketsManager.getTicket()
+          ),
+          results =>
+            if ticketsManager.remainingTickets < 0 then
+              (false, "Sold more tickets than available!")
+            else (true, "")
+        )
+    )
+
+  class ScheduledTicketsManager(totalTickets: Int, val scheduler: Scheduler)
+      extends TicketsManager(totalTickets)
+      with MockedMonitor

src/test/scala/midterm22/Part7Test.scala

+package midterm22
+
+import org.junit.*
+import org.junit.Assert.*
+import instrumentation.*
+
+class Part7Test:
+  @Test
+  def testNicManagerSequential() =
+    val nicsManager = NICManager(4)
+    assertEquals((0, 1), nicsManager.assignNICs())
+    assertEquals((2, 3), nicsManager.assignNICs())
+
+  @Test
+  def testQuestion22() =
+    testNicManagerParallel(2, 3)
+
+  @Test
+  def testQuestion23() =
+    val nicsManager = NICManager(2)
+
+    // Thread 1
+    assertEquals((0, 1), nicsManager.assignNICs())
+    nicsManager.nics(0).assigned = false
+    nicsManager.nics(1).assigned = false
+
+    // Thread 2
+    assertEquals((0, 1), nicsManager.assignNICs())
+    nicsManager.nics(0).assigned = false
+    nicsManager.nics(1).assigned = false
+
+  @Test
+  def testQuestion24() =
+    testNicManagerParallel(3, 2, true)
+
+  @Test
+  def testQuestion24NotLimitingRecvNICs() =
+    TestUtils.assertMaybeDeadlock(
+      testNicManagerParallel(3, 2)
+    )
+
+  def testNicManagerParallel(
+      threads: Int,
+      nics: Int,
+      limitRecvNICs: Boolean = false
+  ) =
+    TestHelper.testManySchedules(
+      threads,
+      scheduler =>
+        val nicsManager = ScheduledNicsManager(nics, scheduler)
+        val tasks =
+          for i <- 0 until threads yield () =>
+            // Thread i
+            val (recvNIC, sendNIC) = nicsManager.assignNICs(limitRecvNICs)
+
+            // Do something with NICs...
+
+            // Un-assign NICs
+            nicsManager.nics(recvNIC).assigned = false
+            nicsManager.nics(sendNIC).assigned = false
+        (
+          tasks.toList,
+          results =>
+            if nicsManager.nics.count(_.assigned) != 0 then
+              (false, f"All NICs should have been released.")
+            else (true, "")
+        )
+    )
+
+  class ScheduledNicsManager(n: Int, scheduler: Scheduler)
+      extends NICManager(n):
+    class ScheduledNIC(
+        _index: Int,
+        _assigned: Boolean,
+        val scheduler: Scheduler
+    ) extends NIC(_index, _assigned)
+        with MockedMonitor:
+      override def index = scheduler.exec { super.index }(
+        "",
+        Some(res => f"read NIC.index == $res")
+      )
+      override def assigned = scheduler.exec { super.assigned }(
+        "",
+        Some(res => f"read NIC.assigned == $res")
+      )
+      override def assigned_=(v: Boolean) =
+        scheduler.exec { super.assigned = v }(
+          f"write NIC.assigned = $v"
+        )
+    override val nics =
+      (for i <- 0 until n yield ScheduledNIC(i, false, scheduler)).toList

src/test/scala/midterm22/Part8Test.scala

+package midterm22
+
+import org.junit.*
+import org.junit.Assert.*
+import instrumentation.*
+import annotation.nowarn
+
+import scala.collection.concurrent.TrieMap
+import scala.collection.concurrent.{TrieMap, Map}
+
+class Part8Test:
+  @Test
+  def usage() =
+    val insta = Instagram()
+    assertEquals(1, insta.add())
+    assertEquals(2, insta.add())
+    insta.follow(1, 2)
+    assertEquals(insta.graph, Map(1 -> List(2), 2 -> List()))
+    insta.follow(2, 1)
+    insta.unfollow(1, 2)
+    assertEquals(insta.graph, Map(1 -> List(), 2 -> List(1)))
+    insta.follow(3, 1) // fails silently
+    assertEquals(insta.graph, Map(1 -> List(), 2 -> List(1)))
+    insta.remove(1)
+    assertEquals(insta.graph, Map(2 -> List()))
+    insta.unfollow(1, 2) // fails silently
+
+  @Test
+  def testParallelFollowABRemoveA() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.follow(u1, u2),
+            () =>
+              // Thread 2
+              insta.remove(u1)
+          ),
+          results =>
+            val size = insta.graph.size
+            if size != 1 then
+              (false, f"Wrong number of user: expected 1 but got ${size}")
+            else validateGraph(insta)
+        )
+    )
+
+  @Test
+  def testParallelFollowABRemoveB() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.follow(u1, u2),
+            () =>
+              // Thread 2
+              insta.remove(u2)
+          ),
+          results =>
+            val size = insta.graph.size
+            if size != 1 then
+              (false, f"Wrong number of user: expected 1 but got ${size}")
+            else validateGraph(insta)
+        )
+    )
+
+  @Test
+  def testParallelFollowACRemoveB() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+        val u3 = insta.add()
+        insta.follow(u1, u2)
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.follow(u1, u3),
+            () =>
+              // Thread 2
+              insta.remove(u2)
+          ),
+          results =>
+            val size = insta.graph.size
+            if size != 2 then
+              (false, f"Wrong number of user: expected 2 but got ${size}")
+            else validateGraph(insta)
+        )
+    )
+
+  @Test
+  def testParallelFollow() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+        val u3 = insta.add()
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.follow(u1, u2),
+            () =>
+              // Thread 2
+              insta.follow(u1, u3)
+          ),
+          results =>
+            val u1FollowingSize = insta.graph(u1).size
+            if u1FollowingSize != 2 then
+              (
+                false,
+                f"Wrong number of users followed by user 1: expected 2 but got ${u1FollowingSize}"
+              )
+            else validateGraph(insta)
+        )
+    )
+
+  @Test
+  def testParallelRemove() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+        // Setup
+        val u1 = insta.add()
+        val u2 = insta.add()
+        val u3 = insta.add()
+        insta.follow(u1, u2)
+        insta.follow(u2, u1)
+        insta.follow(u2, u3)
+        insta.follow(u3, u1)
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.remove(u2),
+            () =>
+              // Thread 2
+              insta.remove(u3)
+          ),
+          results =>
+            val size = insta.graph.size
+            if size != 1 then
+              (false, f"Wrong number of user: expected 1 but got ${size}")
+            else validateGraph(insta)
+        )
+    )
+
+  // We test wrong code here, so we expect an assertion error. You can replace
+  // the next line by `@Test` if you want to see the error with the failing
+  // schedule.
+  @Test(expected = classOf[AssertionError])
+  def testParallelWrongAdd() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+          // This implementation of `add` is wrong, because two threads might
+          // allocate the same id.
+          // Consider the following schedule:
+          // T1: res = 1
+          // T2: res = 2
+          // T2: graph.update(2, Nil)
+          // T2: 2
+          // T1: graph.update(2, Nil)
+          // T1: 2
+          override def add(): Int =
+            val res = maxId.incrementAndGet
+            graph.update(maxId.get, Nil)
+            res
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.add(),
+            () =>
+              // Thread 2
+              insta.add()
+          ),
+          results =>
+            if results(0) != results(1) then
+              (false, f"Allocated twice id ${results(0)}")
+            else validateGraph(insta)
+        )
+    )
+
+  // We test wrong code here, so we expect an assertion error. You can replace
+  // the next line by `@Test` if you want to see the error with the failing
+  // schedule.
+  @Test(expected = classOf[AssertionError])
+  def testParallelWrongRemove() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+
+          // This implementation of `remove` is wrong because we don't retry to
+          // call `graph.replace` when it fails. Therefore, user 1 might end up
+          // following user 2 that has been removed, or not following user 3
+          // which is concurrently followed.
+          override def remove(idToRemove: Int): Unit =
+            graph.remove(idToRemove)
+            for (key, value) <- graph do
+              graph.replace(key, value, value.filter(_ != idToRemove))
+              // Note: writing `graph(key) = value.filter(_ != idToRemove)` would also
+              // be wrong because it does not check the previous value.
+              // Therefore, it could erase a concurrent update.
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+        val u3 = insta.add()
+        insta.follow(u1, u2)
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.follow(u1, u3),
+            () =>
+              // Thread 2
+              insta.remove(u2)
+          ),
+          results =>
+            val size = insta.graph.size
+            if insta.graph(u1).size != 1 then
+              (
+                false,
+                f"Wrong number of users followed by 1: expected 1 but got ${insta.graph(u1)}"
+              )
+            else validateGraph(insta)
+        )
+    )
+
+  // We test wrong code here, so we expect an assertion error. You can replace
+  // the next line by `@Test` if you want to see the error with the failing
+  // schedule.
+  @Test(expected = classOf[AssertionError])
+  def testParallelWrongUnfollow() =
+    TestHelper.testManySchedules(
+      2,
+      scheduler =>
+        val insta = new Instagram:
+          override val graph =
+            ScheduledTrieMap(TrieMap[Int, List[Int]](), scheduler)
+          override def unfollow(a: Int, b: Int): Unit =
+            if !graph.contains(a) then return
+            val prev = graph(a) // Might throw java.util.NoSuchElementException
+            if !graph.replace(a, prev, prev.filter(_ != b)) then unfollow(a, b)
+
+        val u1 = insta.add()
+        val u2 = insta.add()
+        insta.follow(u1, u2)
+
+        (
+          List(
+            () =>
+              // Thread 1
+              insta.unfollow(u1, u2),
+            () =>
+              // Thread 2
+              insta.remove(u1)
+          ),
+          results =>
+            val size = insta.graph.size
+            if size != 1 then
+              (false, f"Wrong number of user: expected 1 but got ${size}")
+            else validateGraph(insta)
+        )
+    )
+
+  @nowarn
+  def validateGraph(insta: Instagram): (Boolean, String) =
+    for (a, following) <- insta.graph; b <- following do
+      if !insta.graph.contains(b) then
+        return (false, f"User $a follows non-existing user $b")
+    (true, "")
+
+  final class ScheduledIterator[T](
+      private val myIterator: Iterator[T],
+      private val scheduler: Scheduler
+  ) extends Iterator[T]:
+    override def hasNext =
+      myIterator.hasNext
+    override def next() =
+      scheduler.exec(myIterator.next)("", Some(res => f"Iterator.next == $res"))
+    override def knownSize: Int =
+      myIterator.knownSize
+
+  final class ScheduledTrieMap[K, V](
+      private val myMap: Map[K, V],
+      private val scheduler: Scheduler
+  ) extends Map[K, V]:
+    override def apply(key: K): V =
+      scheduler.exec(myMap(key))(
+        "",
+        Some(res => f"TrieMap.apply($key) == $res")
+      )
+    override def contains(key: K): Boolean =
+      scheduler.exec(myMap.contains(key))(
+        "",
+        Some(res => f"TrieMap.contains($key) == $res")
+      )
+    override def get(key: K): Option[V] =
+      scheduler.exec(myMap.get(key))(
+        "",
+        Some(res => f"TrieMap.get($key) == $res")
+      )
+    override def addOne(kv: (K, V)) =
+      scheduler.exec(myMap.addOne(kv))(f"TrieMap.addOne($kv)")
+      this
+    override def subtractOne(k: K) =
+      scheduler.exec(myMap.subtractOne(k))(f"TrieMap.subtractOne($k)")
+      this
+    override def iterator() =
+      scheduler.log("TrieMap.iterator")
+      ScheduledIterator(myMap.iterator, scheduler)
+    override def replace(k: K, v: V): Option[V] =
+      scheduler.exec(myMap.replace(k, v))(
+        "",
+        Some(res => f"TrieMap.replace($k, $v) == $res")
+      )
+    override def replace(k: K, oldvalue: V, newvalue: V): Boolean =
+      scheduler.exec(myMap.replace(k, oldvalue, newvalue))(
+        "",
+        Some(res => f"TrieMap.replace($k, $oldvalue, $newvalue) == $res")
+      )
+    override def putIfAbsent(k: K, v: V): Option[V] =
+      scheduler.exec(myMap.putIfAbsent(k, v))(
+        "",
+        Some(res => f"TrieMap.putIfAbsent($k, $v)")
+      )
+    override def remove(k: K): Option[V] =
+      scheduler.exec(myMap.remove(k))(
+        "",
+        Some(res => f"TrieMap.remove($k)")
+      )
+    override def remove(k: K, v: V): Boolean =
+      scheduler.exec(myMap.remove(k, v))(
+        "",
+        Some(res => f"TrieMap.remove($k, $v)")
+      )

src/test/scala/midterm23/BarberShopSolutionTest.scala

+package midterm23
+
+import instrumentation.*
+import java.util.concurrent.atomic.AtomicInteger
+
+class BarberShopSolutionTest extends munit.FunSuite:
+  val implementations =
+    Map[String, (Int, Scheduler) => ScheduledBarberShopSolution](
+      "BarberShopSolution1" -> (new BarberShopSolution1(_)
+        with ScheduledBarberShopSolution(_)),
+      "BarberShopSolution2" -> (new BarberShopSolution2(_)
+        with ScheduledBarberShopSolution(_)),
+      "BarberShopSolution3" -> (new BarberShopSolution3(_)
+        with ScheduledBarberShopSolution(_))
+    )
+
+  for (name, makeShop) <- implementations do
+    for nCustomers <- 1 to 3 do
+      test(f"$name with $nCustomers customer(s)") {
+        testBarberShop(nCustomers, makeShop)
+      }

src/test/scala/midterm23/ScheduledBarberShopSolution.scala

+package midterm23
+
+import instrumentation.{MockedMonitor, Monitor, Scheduler}
+import java.util.concurrent.ConcurrentLinkedQueue
+import scala.jdk.CollectionConverters.IterableHasAsScala
+import scala.annotation.tailrec
+
+trait ScheduledBarberShopSolution(scheduler0: Scheduler)
+    extends AbstractBarberShopSolution:
+  enum Event:
+    case HairCut
+    case CustomerLeaves
+
+  val trace = ConcurrentLinkedQueue[Event]()
+
+  override def notifyBarber = scheduler0.exec { super.notifyBarber }(
+    "",
+    Some(res => f"read notifyBarber == $res")
+  )
+
+  override def notifyBarber_=(v: Boolean) =
+    scheduler0.exec { super.notifyBarber = v }(
+      f"write notifyBarber = $v"
+    )
+
+  override def notifyCustomer = scheduler0.exec { super.notifyCustomer }(
+    "",
+    Some(res => f"read notifyCustomer == $res")
+  )
+
+  override def notifyCustomer_=(v: Boolean) =
+    scheduler0.exec { super.notifyCustomer = v }(
+      f"write notifyCustomer = $v"
+    )
+
+  override def hairCut() =
+    log("hair cut")
+    trace.add(Event.HairCut)
+
+  def customerTrace(n: Int): Unit =
+    this.customer(n)
+    log("customer leaves")
+    trace.add(Event.CustomerLeaves)
+
+  private val _lockObj = new MockedMonitor:
+    override def scheduler: Scheduler = scheduler0
+
+  override def lockObj: Monitor = _lockObj
+
+  override def log(s: String): Unit = scheduler0.log(s)
+
+  def nHaircuts: Int =
+    trace.asScala.filter(_ == Event.HairCut).size
+
+  def customerLeftEarly(): Boolean =
+    @tailrec
+    def loop(it: Iterable[Event], n: Int): Boolean =
+      if it.isEmpty then false
+      else
+        val newN = it.head match
+          case Event.HairCut        => n + 1
+          case Event.CustomerLeaves => n - 1
+        if newN < 0 then true
+        else loop(it.tail, newN)
+    loop(trace.asScala, 0)

src/test/scala/midterm23/testBarberShop.scala

+package midterm23
+
+import instrumentation.{Scheduler, TestHelper}
+
+/** Tests a barber shop implementation.
+  *
+  * @param nCustomers
+  *   The number of customers to simulate.
+  * @param makeShop
+  *   A function that creates a barber shop given the number of customers and a
+  *   scheduler.
+  * @param checkEarlyCustomer
+  *   If true, checks that no customer left early, i.e. that there is always a
+  *   number of terminated customer threads equal or less than to the number of
+  *   haircuts done.
+  */
+def testBarberShop(
+    nCustomers: Int,
+    makeShop: (Int, Scheduler) => ScheduledBarberShopSolution,
+    checkEarlyCustomer: Boolean = true
+) =
+  TestHelper.testManySchedules(
+    nCustomers + 1,
+    scheduler =>
+      val barberShop = makeShop(nCustomers, scheduler)
+
+      (
+        (() => barberShop.barber())
+          :: (for i <- 1 to nCustomers
+          yield () => barberShop.customerTrace(i)).toList,
+        results =>
+          if barberShop.nHaircuts != nCustomers then
+            (false, f"Unexpected number of hair cuts: ${barberShop.nHaircuts}")
+          else if checkEarlyCustomer && barberShop.customerLeftEarly() then
+            (false, f"A customer left early")
+          else
+            (true, "")
+      )
+  )