distributed_system_coursework/lib/paxos_test.ex

defmodule PaxosTest do
  # The functions implement 
  # the module specific testing logic
  defp init(name, participants, all \\ false) do
    cpid = TestHarness.wait_to_register(:coord, :global.whereis_name(:coord))

    try do
      pid = Paxos.start(name, participants)
      Process.sleep(100)
      if not Process.alive?(pid), do: raise("no pid")

      TestHarness.wait_for(
        MapSet.new(participants),
        name,
        if(not all,
          do: length(participants) / 2,
          else: length(participants)
        )
      )

      {cpid, pid}
    rescue
      _ -> {cpid, :c.pid(0, 2048, 0)}
    end
  end

  defp kill_paxos(pid, name) do
    Process.exit(pid, :kill)
    :global.unregister_name(name)
    pid
  end

  defp wait_for_decision(_, _, timeout) when timeout <= 0, do: {:none, :none}

  defp wait_for_decision(pid, inst, timeout) do
    Process.sleep(100)
    v = Paxos.get_decision(pid, inst, 1)

    case v do
      v when v != nil -> {:decide, v}
      nil -> wait_for_decision(pid, inst, timeout - 100)
    end
  end

  defp propose_until_commit(pid, inst, val) do
    status = Paxos.propose(pid, inst, val, 10000)

    case status do
      {:decision, val} -> val
      {:abort, val} -> propose_until_commit(pid, inst, val)
      _ -> nil
    end
  end

  # Test cases start from here

  # No failures, no concurrent ballots
  def run_simple(name, participants, val) do
    {cpid, pid} = init(name, participants)
    send(cpid, :ready)

    {status, val, a} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")
          leader = (fn [h | _] -> h end).(participants)

          if name == leader do
            Paxos.propose(pid, 1, val, 10000)
          end

          {status, v} = wait_for_decision(pid, 1, 10000)

          if status != :none do
            IO.puts("#{name}: decided #{inspect(v)}")
          else
            IO.puts("#{name}: No decision after 10 seconds")
          end

          {status, v, 10}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # No failures, 2 concurrent ballots
  def run_simple_2(name, participants, val) do
    {cpid, pid} = init(name, participants)
    send(cpid, :ready)

    {status, val, a} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")

          if name in (fn [h1, h2 | _] -> [h1, h2] end).(participants),
            do: Paxos.propose(pid, 1, val, 10000)

          {status, val} = wait_for_decision(pid, 1, 10000)

          if status != :none,
            do: IO.puts("#{name}: decided #{inspect(val)}"),
            else: IO.puts("#{name}: No decision after 10 seconds")

          {status, val, 10}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)
        IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # No failures, 2 concurrent instances
  def run_simple_3(name, participants, val) do
    {cpid, pid} = init(name, participants)
    send(cpid, :ready)

    {status, val, a} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")
          proposers = Enum.zip((fn [h1, h2 | _] -> [h1, h2] end).(participants), [1, 2])
          proposers = for {k, v} <- proposers, into: %{}, do: {k, v}
          if proposers[name], do: Paxos.propose(pid, proposers[name], val, 10000)

          y =
            List.to_integer(
              (fn [_ | x] -> x end).(
                Atom.to_charlist((fn [h | _] -> h end).(Map.keys(proposers)))
              )
            )

          :rand.seed(:exrop, {y * 100 + 1, y * 100 + 2, y * 100 + 3})
          inst = Enum.random(1..2)
          {status, val} = wait_for_decision(pid, inst, 10000)

          if status != :none,
            do: IO.puts("#{name}: decided #{inspect(val)}"),
            else: IO.puts("#{name}: No decision after 10 seconds")

          {status, val, 10}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)
        IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # No failures, many concurrent ballots
  def run_simple_many_1(name, participants, val) do
    {cpid, pid} = init(name, participants)
    send(cpid, :ready)

    {status, val, a} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")
          Paxos.propose(pid, 2, val, 10000)
          Process.sleep(Enum.random(1..10))
          {status, val} = wait_for_decision(pid, 2, 10000)

          if status != :none,
            do: IO.puts("#{name}: decided #{inspect(val)}"),
            else: IO.puts("#{name}: No decision after 10 seconds")

          {status, val, 10}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)
        IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # No failures, many concurrent ballots
  def run_simple_many_2(name, participants, val) do
    {cpid, pid} = init(name, participants)
    send(cpid, :ready)

    {status, val, a} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")

          for _ <- 1..10 do
            Process.sleep(Enum.random(1..10))
            Paxos.propose(pid, 1, val, 10000)
          end

          {status, val} = wait_for_decision(pid, 1, 10000)

          if status != :none,
            do: IO.puts("#{name}: decided #{inspect(val)}"),
            else: IO.puts("#{name}: No decision after 10 seconds")

          {status, val, 10}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)
        IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # One non-leader process crashes, no concurrent ballots
  def run_non_leader_crash(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")

          [leader, kill_p | spare] = participants

          case name do
            ^leader ->
              Paxos.propose(pid, 1, val, 10000)

            ^kill_p ->
              Process.sleep(Enum.random(1..5))
              Process.exit(pid, :kill)

            _ ->
              nil
          end

          spare = [leader | spare]

          if name in spare do
            {status, val} = wait_for_decision(pid, 1, 10000)

            if status != :none,
              do: IO.puts("#{name}: decided #{inspect(val)}"),
              else: IO.puts("#{name}: No decision after 10 seconds")

            {status, val, 10, spare}
          else
            {:killed, :none, -1, spare}
          end
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # Minority non-leader crashes, no concurrent ballots
  def run_minority_non_leader_crash(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      try do
        receive do
          :start ->
            IO.puts("#{inspect(name)}: started")

            [leader | rest] = participants

            to_kill = Enum.slice(rest, 0, div(length(participants), 2))

            if name == leader do
              Paxos.propose(pid, 1, val, 10000)
            end

            if name in to_kill do
              Process.sleep(Enum.random(1..5))
              Process.exit(pid, :kill)
            end

            spare = for p <- participants, p not in to_kill, do: p

            if name in spare do
              {status, val} = wait_for_decision(pid, 1, 10000)

              if status != :none,
                do: IO.puts("#{name}: decided #{inspect(val)}"),
                else: IO.puts("#{name}: No decision after 10 seconds")

              {status, val, 10, spare}
            else
              {:killed, :none, -1, spare}
            end
        end
      rescue
        _ -> {:none, :none, 10, []}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # Leader crashes, no concurrent ballots
  def run_leader_crash_simple(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      try do
        receive do
          :start ->
            IO.puts("#{inspect(name)}: started")

            [leader | spare] = participants
            [new_leader | _] = spare

            if name == leader do
              Paxos.propose(pid, 1, val, 10000)
              Process.sleep(Enum.random(1..5))
              Process.exit(pid, :kill)
            end

            if name == new_leader do
              Process.sleep(10)
              propose_until_commit(pid, 1, val)
            end

            if name in spare do
              {status, val} = wait_for_decision(pid, 1, 10000)

              if status != :none,
                do: IO.puts("#{name}: decided #{inspect(val)}"),
                else: IO.puts("#{name}: No decision after 10 seconds")

              {status, val, 10, spare}
            else
              {:killed, :none, -1, spare}
            end
        end
      rescue
        _ -> {:none, :none, 10, []}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # Leader and some non-leaders crash, no concurrent ballots
  # # Needs to be run with at least 5 process config
  def run_leader_crash_simple_2(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started")
          leader = (fn [h | _] -> h end).(participants)

          if name == leader do
            Paxos.propose(pid, 1, val, 10000)
            Process.sleep(Enum.random(1..5))
            Process.exit(pid, :kill)
          end

          spare =
            Enum.reduce(
              List.delete(participants, leader),
              List.delete(participants, leader),
              fn _, s -> if length(s) > length(participants) / 2 + 1, do: tl(s), else: s end
            )

          leader = hd(spare)

          if name not in spare do
            Process.sleep(Enum.random(1..5))
            Process.exit(pid, :kill)
          end

          if name == leader do
            Process.sleep(10)
            propose_until_commit(pid, 1, val)
          end

          if name in spare do
            {status, val} = wait_for_decision(pid, 1, 10000)

            if status != :none,
              do: IO.puts("#{name}: decided #{inspect(val)}"),
              else: IO.puts("#{name}: No decision after 10 seconds")

            {status, val, 10, spare}
          else
            {:killed, :none, -1, spare}
          end
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # Cascading failures of leaders and non-leaders
  def run_leader_crash_complex(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      receive do
        :start ->
          IO.puts("#{inspect(name)}: started with #{inspect(participants)}")

          {kill, spare} =
            Enum.reduce(participants, {[], participants}, fn _, {k, s} ->
              if length(s) > length(participants) / 2 + 1, do: {k ++ [hd(s)], tl(s)}, else: {k, s}
            end)

          leaders = Enum.slice(kill, 0, div(length(kill), 2))
          followers = Enum.slice(kill, div(length(kill), 2), div(length(kill), 2) + 1)

          # IO.puts("spare = #{inspect spare}")
          # IO.puts "kill: leaders, followers = #{inspect leaders}, #{inspect followers}"

          if name in leaders do
            Paxos.propose(pid, 1, val, 10000)
            Process.sleep(Enum.random(1..5))
            Process.exit(pid, :kill)
          end

          if name in followers do
            Process.sleep(Enum.random(1..5))
            Process.exit(pid, :kill)
          end

          if hd(spare) == name do
            Process.sleep(10)
            propose_until_commit(pid, 1, val)
          end

          if name in spare do
            {status, val} = wait_for_decision(pid, 1, 50000)

            if status != :none,
              do: IO.puts("#{name}: decided #{inspect(val)}"),
              else: IO.puts("#{name}: No decision after 50 seconds")

            {status, val, 10, spare}
          else
            {:killed, :none, -1, spare}
          end
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end

  # # Cascading failures of leaders and non-leaders, random delays
  def run_leader_crash_complex_2(name, participants, val) do
    {cpid, pid} = init(name, participants, true)
    send(cpid, :ready)

    {status, val, a, spare} =
      try do
        receive do
          :start ->
            IO.puts("#{inspect(name)}: started")

            {kill, spare} =
              Enum.reduce(participants, {[], participants}, fn _, {k, s} ->
                if length(s) > length(participants) / 2 + 1,
                  do: {k ++ [hd(s)], tl(s)},
                  else: {k, s}
              end)

            leaders = Enum.slice(kill, 0, div(length(kill), 2))
            followers = Enum.slice(kill, div(length(kill), 2), div(length(kill), 2) + 1)

            IO.puts("spare = #{inspect(spare)}")
            IO.puts("kill: leaders, followers = #{inspect(leaders)}, #{inspect(followers)}")

            if name in leaders do
              Paxos.propose(pid, 1, val, 10000)
              Process.sleep(Enum.random(1..5))
              Process.exit(pid, :kill)
            end

            if name in followers do
              for _ <- 1..10 do
                :erlang.suspend_process(pid)
                Process.sleep(Enum.random(1..5))
                :erlang.resume_process(pid)
              end

              Process.exit(pid, :kill)
            end

            if hd(spare) == name do
              Process.sleep(10)
              Paxos.propose(pid, 1, val, 10000)
            end

            if name in spare do
              for _ <- 1..10 do
                :erlang.suspend_process(pid)
                Process.sleep(Enum.random(1..5))
                :erlang.resume_process(pid)
                leader = hd(Enum.reverse(spare))
                if name == leader, do: Paxos.propose(pid, 1, val, 10000)
              end

              leader = hd(spare)
              if name == leader, do: propose_until_commit(pid, 1, val)
              {status, val} = wait_for_decision(pid, 1, 50000)

              if status != :none,
                do: IO.puts("#{name}: decided #{inspect(val)}"),
                else: IO.puts("#{name}: No decision after 50 seconds")

              {status, val, 10, spare}
            else
              {:killed, :none, -1, spare}
            end
        end
      rescue
        _ -> {:none, :none, 10, []}
      end

    send(cpid, :done)

    receive do
      :all_done ->
        Process.sleep(100)

        ql =
          if name in spare do
            IO.puts("#{name}: #{inspect(ql = Process.info(pid, :message_queue_len))}")
            ql
          else
            {:message_queue_len, -1}
          end

        kill_paxos(pid, name)
        send(cpid, {:finished, name, pid, status, val, a, ql})
    end
  end
end