add tests for multipaxos

Modules/RDTs/src/main/scala/rdts/datatypes/experiments/protocols/Paxos.scala

@@ -39,7 +39,8 @@ case class Paxos[A](
     rounds.filter { case (b, p) => b.uid == replicaId }.maxOption
   def lastValueVote: Option[(BallotNum, PaxosRound[A])] = rounds.filter(_._2.proposals.votes.nonEmpty).maxOption
   def newestReceivedVal(using LocalUid)                 = lastValueVote.map(_._2.proposals.votes.head.value)
-  def myValue(using LocalUid): A                        = rounds(BallotNum(replicaId, -1)).proposals.votes.head.value
+  def myValue(using LocalUid): Option[A] =
+    rounds.get(BallotNum(replicaId, -1)).map(_.proposals.votes.head.value)
   def decidedVal(using Participants): Option[A] =
     rounds.collectFirst { case (b, PaxosRound(_, voting)) if voting.result.isDefined => voting.result.get }
   def decidedLeaderElection(using Participants): Option[(BallotNum, LeaderElection)] =
@@ -70,8 +71,10 @@ case class Paxos[A](
       case _ => Paxos() // do nothing
 
   def phase2a(using LocalUid, Participants): Paxos[A] =
-    // propose a value if I am the leader
-    phase2a(myValue)
+    // try to determine my process' value from previous ballot
+    myValue match
+      case Some(value) => phase2a(value)
+      case None        => Paxos()
 
   def phase2a(value: A)(using LocalUid, Participants): Paxos[A] =
     // propose a value if I am the leader

Modules/RDTs/src/test/scala/test/rdts/protocols/MultiPaxosTest.scala

@@ -0,0 +1,93 @@
+package test.rdts.protocols
+
+import rdts.base.LocalUid
+import rdts.datatypes.experiments.protocols.Paxos.given
+import rdts.datatypes.experiments.protocols.{MultiPaxos, MultipaxosPhase, Participants, Paxos}
+
+class MultiPaxosTest extends munit.FunSuite {
+
+  val id1 = LocalUid.gen()
+  val id2 = LocalUid.gen()
+  val id3 = LocalUid.gen()
+
+  given Participants = Participants(Set(id1, id2, id3).map(_.uid))
+
+  val emptyPaxosObject: MultiPaxos[Int] = MultiPaxos()
+  test("happy path") {
+    var testPaxosObject = emptyPaxosObject
+
+    assertEquals(testPaxosObject.leader, None)
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.LeaderElection, "multipaxos starts in leader election phase")
+
+    val proposeValue = 1
+    // replica 1 tries to become leader
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.startLeaderElection(using id1))
+
+    // testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id1))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id2))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id3))
+
+    assertEquals(testPaxosObject.leader, Some(id1.uid), "id1 should be the leader")
+
+    // replica 2 tries to write
+    val afterwrite = testPaxosObject.merge(testPaxosObject.proposeIfLeader(2)(using id2))
+    assertEquals(afterwrite, testPaxosObject)
+
+    // replica 1 (leader) writes
+    val afterLeaderWrite = testPaxosObject.merge(testPaxosObject.proposeIfLeader(1)(using id1))
+    assertNotEquals(afterLeaderWrite, testPaxosObject)
+    testPaxosObject = afterLeaderWrite
+
+    assertEquals(testPaxosObject.log, Map.empty)
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.Voting)
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id3))
+    assertEquals(testPaxosObject.log.values.toList, List(1))
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.Idle)
+
+    testPaxosObject.merge(testPaxosObject.proposeIfLeader(2)(using id2))
+
+    // replica 1 (leader) writes again
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.proposeIfLeader(12)(using id1))
+    assertEquals(testPaxosObject.log.values.toList, List(1))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id2))
+    assertEquals(testPaxosObject.log.values.toList.sorted, List(1, 12))
+
+    // replica 3 starts new leader election
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.startLeaderElection(using id3))
+    assertEquals(testPaxosObject.log.values.toList.sorted, List(1, 12), "log survives new leader election")
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.LeaderElection)
+    assertEquals(testPaxosObject.leader, None)
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id3))
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.LeaderElection)
+    assertEquals(testPaxosObject.leader, None)
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id2))
+    assertEquals(testPaxosObject.phase, MultipaxosPhase.Idle)
+    assertEquals(testPaxosObject.leader, Some(id3.uid))
+  }
+
+  test("conflicting proposals") {
+    var testPaxosObject = emptyPaxosObject
+
+    // replicas 1 and 2 try to become leader
+    var rep1 = emptyPaxosObject.merge(emptyPaxosObject.startLeaderElection(using id1))
+    var rep2 = emptyPaxosObject.merge(emptyPaxosObject.startLeaderElection(using id2))
+
+    // sync
+    testPaxosObject = testPaxosObject.merge(rep1).merge(rep2)
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id1))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id2))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id3))
+
+    // propose values
+    rep1 = testPaxosObject.proposeIfLeader(1)(using id1)
+    rep2 = testPaxosObject.proposeIfLeader(2)(using id2)
+
+    // sync
+    testPaxosObject = testPaxosObject.merge(rep1).merge(rep2)
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id1))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id2))
+    testPaxosObject = testPaxosObject.merge(testPaxosObject.upkeep(using id3))
+
+    assert(testPaxosObject.log.values.head == 1 || testPaxosObject.log.values.head == 2)
+  }
+}