diff --git a/lib/concurrency.rb b/lib/concurrency.rb
deleted file mode 100644
index 3bca0031055..00000000000
--- a/lib/concurrency.rb
+++ /dev/null
@@ -1,21 +0,0 @@
-# frozen_string_literal: true
-
-# This is the 'actually concurrent' counterpart to
-# Concurrency::Scenario::Execution from spec/support/concurrency.rb
-module Concurrency
-  class ThreadedExecution
-    def new_mutex
-      Mutex.new
-    end
-
-    def sleep(delay)
-      super(delay)
-      nil
-    end
-
-    def spawn(&blk)
-      Thread.new(&blk)
-      nil
-    end
-  end
-end
diff --git a/lib/discourse_redis.rb b/lib/discourse_redis.rb
index 912aea25843..728e244db74 100644
--- a/lib/discourse_redis.rb
+++ b/lib/discourse_redis.rb
@@ -3,248 +3,139 @@
 #
 #  A wrapper around redis that namespaces keys with the current site id
 #
-require_dependency 'cache'
-require_dependency 'concurrency'
 
 class DiscourseRedis
-  class RedisStatus
+  class FallbackHandler
+    include Singleton
+
     MASTER_ROLE_STATUS = "role:master".freeze
+    MASTER_LOADING_STATUS = "loading:1".freeze
     MASTER_LOADED_STATUS = "loading:0".freeze
     CONNECTION_TYPES = %w{normal pubsub}.each(&:freeze)
 
-    def initialize(master_config, slave_config)
-      master_config = master_config.dup.freeze unless master_config.frozen?
-      slave_config = slave_config.dup.freeze unless slave_config.frozen?
-
-      @master_config = master_config
-      @slave_config = slave_config
-    end
-
-    def master_alive?
-      master_client = connect(@master_config)
-
-      begin
-        info = master_client.call([:info])
-      rescue Redis::ConnectionError, Redis::CannotConnectError, RuntimeError => ex
-        raise ex if ex.class == RuntimeError && ex.message != "Name or service not known"
-        warn "Master not alive, error connecting"
-        return false
-      ensure
-        master_client.disconnect
-      end
-
-      unless info.include?(MASTER_LOADED_STATUS)
-        warn "Master not alive, status is loading"
-        return false
-      end
-
-      unless info.include?(MASTER_ROLE_STATUS)
-        warn "Master not alive, role != master"
-        return false
-      end
-
-      true
-    end
-
-    def fallback
-      warn "Killing connections to slave..."
-
-      slave_client = connect(@slave_config)
-
-      begin
-        CONNECTION_TYPES.each do |connection_type|
-          slave_client.call([:client, [:kill, 'type', connection_type]])
-        end
-      rescue Redis::ConnectionError, Redis::CannotConnectError, RuntimeError => ex
-        raise ex if ex.class == RuntimeError && ex.message != "Name or service not known"
-        warn "Attempted a redis fallback, but connection to slave failed"
-      ensure
-        slave_client.disconnect
-      end
-    end
-
-    private
-
-    def connect(config)
-      config = config.dup
-      config.delete(:connector)
-      ::Redis::Client.new(config)
-    end
-
-    def log_prefix
-      @log_prefix ||= begin
-        master_string = "#{@master_config[:host]}:#{@master_config[:port]}"
-        slave_string = "#{@slave_config[:host]}:#{@slave_config[:port]}"
-        "RedisStatus master=#{master_string} slave=#{slave_string}"
-      end
-    end
-
-    def warn(message)
-      Rails.logger.warn "#{log_prefix}: #{message}"
-    end
-  end
-
-  class FallbackHandler
-    def initialize(log_prefix, redis_status, execution)
-      @log_prefix = log_prefix
-      @redis_status = redis_status
-      @mutex = execution.new_mutex
-      @execution = execution
+    def initialize
       @master = true
-      @event_handlers = []
+      @running = false
+      @mutex = Mutex.new
+      @slave_config = DiscourseRedis.slave_config
+      @message_bus_keepalive_interval = MessageBus.keepalive_interval
     end
 
-    def add_callbacks(handler)
-      @mutex.synchronize do
-        @event_handlers << handler
-      end
-    end
+    def verify_master
+      synchronize do
+        return if @thread && @thread.alive?
 
-    def start_reset
-      @mutex.synchronize do
-        if @master
-          @master = false
-          trigger(:down)
-          true
-        else
-          false
-        end
-      end
-    end
-
-    def use_master?
-      master = @mutex.synchronize { @master }
-      if !master
-        false
-      elsif safe_master_alive?
-        true
-      else
-        if start_reset
-          @execution.spawn do
-            loop do
-              @execution.sleep 5
-              info "Checking connection to master"
-              if safe_master_alive?
-                @mutex.synchronize do
-                  @master = true
-                  @redis_status.fallback
-                  trigger(:up)
-                end
-                break
-              end
+        @thread = Thread.new do
+          loop do
+            begin
+              thread = Thread.new { initiate_fallback_to_master }
+              thread.join
+              break if synchronize { @master }
+              sleep 5
+            ensure
+              thread.kill
             end
           end
         end
+      end
+    end
 
-        false
+    def initiate_fallback_to_master
+      success = false
+
+      begin
+        redis_config = DiscourseRedis.config.dup
+        redis_config.delete(:connector)
+        master_client = ::Redis::Client.new(redis_config)
+        logger.warn "#{log_prefix}: Checking connection to master server..."
+        info = master_client.call([:info])
+
+        if info.include?(MASTER_LOADED_STATUS) && info.include?(MASTER_ROLE_STATUS)
+          begin
+            logger.warn "#{log_prefix}: Master server is active, killing all connections to slave..."
+
+            self.master = true
+            slave_client = ::Redis::Client.new(@slave_config)
+
+            CONNECTION_TYPES.each do |connection_type|
+              slave_client.call([:client, [:kill, 'type', connection_type]])
+            end
+
+            MessageBus.keepalive_interval = @message_bus_keepalive_interval
+            Discourse.clear_readonly!
+            Discourse.request_refresh!
+            success = true
+          ensure
+            slave_client&.disconnect
+          end
+        end
+      rescue => e
+        logger.warn "#{log_prefix}: Connection to Master server failed with '#{e.message}'"
+      ensure
+        master_client&.disconnect
+      end
+
+      success
+    end
+
+    def master
+      synchronize { @master }
+    end
+
+    def master=(args)
+      synchronize do
+        @master = args
+
+        # Disables MessageBus keepalive when Redis is in readonly mode
+        MessageBus.keepalive_interval = 0 if !@master
       end
     end
 
     private
 
-    attr_reader :log_prefix
-
-    def trigger(event)
-      @event_handlers.each do |handler|
-        begin
-          handler.public_send(event)
-        rescue Exception => e
-          Discourse.warn_exception(e, message: "Error running FallbackHandler callback")
-        end
-      end
+    def synchronize
+      @mutex.synchronize { yield }
     end
 
-    def info(message)
-      Rails.logger.info "#{log_prefix}: #{message}"
+    def logger
+      Rails.logger
     end
 
-    def safe_master_alive?
-      begin
-        @redis_status.master_alive?
-      rescue Exception => e
-        Discourse.warn_exception(e, message: "Error running master_alive?")
-        false
-      end
-    end
-  end
-
-  class MessageBusFallbackCallbacks
-    def down
-      @keepalive_interval, MessageBus.keepalive_interval =
-        MessageBus.keepalive_interval, 0
-    end
-
-    def up
-      MessageBus.keepalive_interval = @keepalive_interval
-    end
-  end
-
-  class MainRedisReadOnlyCallbacks
-    def down
-    end
-
-    def up
-      Discourse.clear_readonly!
-      Discourse.request_refresh!
-    end
-  end
-
-  class FallbackHandlers
-    include Singleton
-
-    def initialize
-      @mutex = Mutex.new
-      @fallback_handlers = {}
-    end
-
-    def handler_for(config)
-      config = config.dup.freeze unless config.frozen?
-
-      @mutex.synchronize do
-        @fallback_handlers[[config[:host], config[:port]]] ||= begin
-          log_prefix = "FallbackHandler #{config[:host]}:#{config[:port]}"
-          slave_config = DiscourseRedis.slave_config(config)
-          redis_status = RedisStatus.new(config, slave_config)
-
-          handler =
-            FallbackHandler.new(
-              log_prefix,
-              redis_status,
-              Concurrency::ThreadedExecution.new
-            )
-
-          if config == GlobalSetting.redis_config
-            handler.add_callbacks(MainRedisReadOnlyCallbacks.new)
-          end
-
-          if config == GlobalSetting.message_bus_redis_config
-            handler.add_callbacks(MessageBusFallbackCallbacks.new)
-          end
-
-          handler
-        end
-      end
-    end
-
-    def self.handler_for(config)
-      instance.handler_for(config)
+    def log_prefix
+      "#{self.class}"
     end
   end
 
   class Connector < Redis::Client::Connector
     def initialize(options)
-      options = options.dup.freeze unless options.frozen?
-
       super(options)
-      @slave_options = DiscourseRedis.slave_config(options).freeze
-      @fallback_handler = DiscourseRedis::FallbackHandlers.handler_for(options)
+      @slave_options = DiscourseRedis.slave_config(options)
+      @fallback_handler = DiscourseRedis::FallbackHandler.instance
     end
 
-    def resolve
-      if @fallback_handler.use_master?
-        @options
-      else
-        @slave_options
+    def resolve(client = nil)
+      if !@fallback_handler.master
+        @fallback_handler.verify_master
+        return @slave_options
+      end
+
+      begin
+        options = @options.dup
+        options.delete(:connector)
+        client ||= Redis::Client.new(options)
+
+        loading = client.call([:info, :persistence]).include?(
+          DiscourseRedis::FallbackHandler::MASTER_LOADING_STATUS
+        )
+
+        loading ? @slave_options : @options
+      rescue Redis::ConnectionError, Redis::CannotConnectError, RuntimeError => ex
+        raise ex if ex.class == RuntimeError && ex.message != "Name or service not known"
+        @fallback_handler.master = false
+        @fallback_handler.verify_master
+        raise ex
+      ensure
+        client.disconnect
       end
     end
   end
@@ -268,6 +159,10 @@ class DiscourseRedis
     @namespace = namespace
   end
 
+  def self.fallback_handler
+    @fallback_handler ||= DiscourseRedis::FallbackHandler.instance
+  end
+
   def without_namespace
     # Only use this if you want to store and fetch data that's shared between sites
     @redis
@@ -281,6 +176,7 @@ class DiscourseRedis
         STDERR.puts "WARN: Redis is in a readonly state. Performed a noop"
       end
 
+      fallback_handler.verify_master if !fallback_handler.master
       Discourse.received_redis_readonly!
       nil
     else
@@ -406,4 +302,5 @@ class DiscourseRedis
   def remove_namespace(key)
     key[(namespace.length + 1)..-1]
   end
+
 end
diff --git a/spec/components/discourse_redis_spec.rb b/spec/components/discourse_redis_spec.rb
index d769afdebfa..6d4af1d8174 100644
--- a/spec/components/discourse_redis_spec.rb
+++ b/spec/components/discourse_redis_spec.rb
@@ -3,84 +3,20 @@
 require 'rails_helper'
 
 describe DiscourseRedis do
-  before do
-    DiscourseRedis::FallbackHandlers.instance.instance_variable_set(:@fallback_handlers, {})
-  end
-
   let(:slave_host) { 'testhost' }
   let(:slave_port) { 1234 }
 
   let(:config) do
-    GlobalSetting.redis_config.dup.merge(slave_host: 'testhost', slave_port: 1234, connector: DiscourseRedis::Connector)
+    DiscourseRedis.config.dup.merge(slave_host: 'testhost', slave_port: 1234, connector: DiscourseRedis::Connector)
   end
 
-  let(:slave_config) { DiscourseRedis.slave_config(config) }
+  let(:fallback_handler) { DiscourseRedis::FallbackHandler.instance }
 
   it "ignore_readonly returns nil from a pure exception" do
     result = DiscourseRedis.ignore_readonly { raise Redis::CommandError.new("READONLY") }
     expect(result).to eq(nil)
   end
 
-  let!(:master_conn) { mock('master') }
-
-  def self.use_fake_threads
-    attr_reader :execution
-
-    around(:each) do |example|
-      scenario =
-        Concurrency::Scenario.new do |execution|
-          @execution = execution
-          example.run
-        end
-
-      scenario.run(sleep_order: true, runs: 1)
-    end
-
-    after(:each) do
-      # Doing this here, as opposed to after example.run, ensures that it
-      # happens before the mocha expectations are checked.
-      execution.wait_done
-    end
-  end
-
-  def stop_after(time)
-    execution.sleep(time)
-    execution.stop_other_tasks
-  end
-
-  def expect_master_info(conf = config)
-    conf = conf.dup
-    conf.delete(:connector)
-
-    Redis::Client.expects(:new)
-      .with(conf)
-      .returns(master_conn)
-
-    master_conn.expects(:disconnect)
-    master_conn
-      .expects(:call)
-      .with([:info])
-  end
-
-  def info_response(*values)
-    values.map { |x| x.join(':') }.join("\r\n")
-  end
-
-  def expect_fallback(config = slave_config)
-    slave_conn = mock('slave')
-
-    config = config.dup
-    config.delete(:connector)
-
-    Redis::Client.expects(:new)
-      .with(config)
-      .returns(slave_conn)
-
-    slave_conn.expects(:call).with([:client, [:kill, 'type', 'normal']])
-    slave_conn.expects(:call).with([:client, [:kill, 'type', 'pubsub']])
-    slave_conn.expects(:disconnect)
-  end
-
   describe 'redis commands' do
     let(:raw_redis) { Redis.new(DiscourseRedis.config) }
 
@@ -161,349 +97,150 @@ describe DiscourseRedis do
     end
   end
 
-  describe DiscourseRedis::RedisStatus do
-    let(:redis_status) { DiscourseRedis::RedisStatus.new(config, slave_config) }
-
-    context "#master_alive?" do
-      it "returns false when the master's hostname cannot be resolved" do
-        expect_master_info
-          .raises(RuntimeError.new('Name or service not known'))
-
-        expect(redis_status.master_alive?).to eq(false)
-      end
-
-      it "raises an error if a runtime error is raised" do
-        error = RuntimeError.new('a random runtime error')
-        expect_master_info.raises(error)
-
-        expect {
-          redis_status.master_alive?
-        }.to raise_error(error)
-      end
-
-      it "returns false if the master is unavailable" do
-        expect_master_info.raises(Redis::ConnectionError.new)
-
-        expect(redis_status.master_alive?).to eq(false)
-      end
-
-      it "returns false if the master is loading" do
-        expect_master_info
-          .returns(info_response(['loading', '1'], ['role', 'master']))
-
-        expect(redis_status.master_alive?).to eq(false)
-      end
-
-      it "returns false if the master is a slave" do
-        expect_master_info
-          .returns(info_response(['loading', '0'], ['role', 'slave']))
-
-        expect(redis_status.master_alive?).to eq(false)
-      end
-
-      it "returns true when the master isn't loading and the role is master" do
-        expect_master_info
-          .returns(info_response(['loading', '0'], ['role', 'master']))
-
-        expect(redis_status.master_alive?).to eq(true)
-      end
-    end
-
-    context "#fallback" do
-      it "instructs redis to kill client connections" do
-        expect_fallback
-
-        redis_status.fallback
+  context 'when redis connection is to a slave redis server' do
+    it 'should check the status of the master server' do
+      begin
+        fallback_handler.master = false
+        Discourse.redis.without_namespace.expects(:set).raises(Redis::CommandError.new("READONLY"))
+        fallback_handler.expects(:verify_master).once
+        Discourse.redis.set('test', '1')
+      ensure
+        fallback_handler.master = true
+        Discourse.redis.del('test')
       end
     end
   end
 
   describe DiscourseRedis::Connector do
     let(:connector) { DiscourseRedis::Connector.new(config) }
-    let(:fallback_handler) { mock('fallback_handler') }
 
-    before do
-      DiscourseRedis::FallbackHandlers.stubs(:handler_for).returns(fallback_handler)
+    after do
+      fallback_handler.master = true
     end
 
     it 'should return the master config when master is up' do
-      fallback_handler.expects(:use_master?).returns(true)
       expect(connector.resolve).to eq(config)
     end
 
+    class BrokenRedis
+      def initialize(error)
+        @error = error
+      end
+
+      def call(*args)
+        raise @error
+      end
+
+      def disconnect
+      end
+    end
+
     it 'should return the slave config when master is down' do
-      fallback_handler.expects(:use_master?).returns(false)
-      expect(connector.resolve).to eq(slave_config)
+      error = Redis::CannotConnectError
+
+      expect do
+        connector.resolve(BrokenRedis.new(error))
+      end.to raise_error(Redis::CannotConnectError)
+
+      config = connector.resolve
+
+      expect(config[:host]).to eq(slave_host)
+      expect(config[:port]).to eq(slave_port)
+    end
+
+    it "should return the slave config when master's hostname cannot be resolved" do
+      error = RuntimeError.new('Name or service not known')
+
+      expect do
+        connector.resolve(BrokenRedis.new(error))
+      end.to raise_error(error)
+
+      expect(fallback_handler.master).to eq(false)
+
+      config = connector.resolve
+
+      expect(config[:host]).to eq(slave_host)
+      expect(config[:port]).to eq(slave_port)
+      expect(fallback_handler.master).to eq(false)
+    end
+
+    it "should return the slave config when master is still loading data" do
+      Redis::Client.any_instance
+        .expects(:call)
+        .with([:info, :persistence])
+        .returns("
+          someconfig:haha\r
+          #{DiscourseRedis::FallbackHandler::MASTER_LOADING_STATUS}
+        ")
+
+      config = connector.resolve
+
+      expect(config[:host]).to eq(slave_host)
+      expect(config[:port]).to eq(slave_port)
+    end
+
+    it "should raise the right error" do
+      error = RuntimeError.new('test')
+
+      2.times do
+        expect { connector.resolve(BrokenRedis.new(error)) }
+          .to raise_error(error)
+      end
     end
   end
 
   describe DiscourseRedis::FallbackHandler do
-    use_fake_threads
-
-    let!(:redis_status) { mock }
-    let!(:fallback_handler) { DiscourseRedis::FallbackHandler.new("", redis_status, execution) }
-
-    context "in the initial configuration" do
-      it "tests that the master is alive and returns true if it is" do
-        redis_status.expects(:master_alive?).returns(true)
-
-        expect(fallback_handler.use_master?).to eq(true)
-      end
-
-      it "tests that the master is alive and returns false if it is not" do
-        redis_status.expects(:master_alive?).returns(false)
-        expect(fallback_handler.use_master?).to eq(false)
-
-        stop_after(1)
-      end
-
-      it "tests that the master is alive and returns false if it raises an exception" do
-        error = Exception.new
-        redis_status.expects(:master_alive?).raises(error)
-
-        Discourse.expects(:warn_exception)
-          .with(error, message: "Error running master_alive?")
-
-        expect(fallback_handler.use_master?).to eq(false)
-
-        stop_after(1)
-      end
-    end
-
-    context "after master_alive? has returned false" do
-      before do
-        redis_status.expects(:master_alive?).returns(false)
-        expect(fallback_handler.use_master?).to eq(false)
-      end
-
-      it "responds with false to the next call to use_master? without consulting redis_status" do
-        expect(fallback_handler.use_master?).to eq(false)
-
-        stop_after(1)
-      end
-
-      it "checks that master is alive again after a timeout" do
-        redis_status.expects(:master_alive?).returns(false)
-
-        stop_after(6)
-      end
-
-      it "checks that master is alive again and checks again if an exception is raised" do
-        error = Exception.new
-        redis_status.expects(:master_alive?).raises(error)
-
-        Discourse.expects(:warn_exception)
-          .with(error, message: "Error running master_alive?")
-
-        execution.sleep(6)
-
-        redis_status.expects(:master_alive?).returns(true)
-        redis_status.expects(:fallback)
-
-        stop_after(5)
-      end
-
-      it "triggers a fallback after master_alive? returns true" do
-        redis_status.expects(:master_alive?).returns(true)
-        redis_status.expects(:fallback)
-
-        stop_after(6)
-      end
-
-      context "after falling back" do
-        before do
-          redis_status.expects(:master_alive?).returns(true)
-          redis_status.expects(:fallback)
-
-          stop_after(6)
-        end
-
-        it "tests that the master is alive and returns true if it is" do
-          redis_status.expects(:master_alive?).returns(true)
-
-          expect(fallback_handler.use_master?).to eq(true)
-        end
-
-        it "tests that the master is alive and returns false if it is not" do
-          redis_status.expects(:master_alive?).returns(false)
-          expect(fallback_handler.use_master?).to eq(false)
-
-          stop_after(1)
-        end
-
-        it "tests that the master is alive and returns false if it raises an exception" do
-          error = Exception.new
-          redis_status.expects(:master_alive?).raises(error)
-
-          Discourse.expects(:warn_exception)
-            .with(error, message: "Error running master_alive?")
-
-          expect(fallback_handler.use_master?).to eq(false)
-
-          stop_after(1)
-        end
-
-        it "doesn't do anything to redis_status for a really long time" do
-          stop_after(1e9)
-        end
-      end
-    end
-  end
-
-  context "when message bus and main are on the same host" do
-    use_fake_threads
-
     before do
-      # Since config is based on GlobalSetting, we need to fetch it before
-      # stubbing
-      conf = config
-
-      GlobalSetting.stubs(:redis_config).returns(conf)
-      GlobalSetting.stubs(:message_bus_redis_config).returns(conf)
-
-      Concurrency::ThreadedExecution.stubs(:new).returns(execution)
+      @original_keepalive_interval = MessageBus.keepalive_interval
     end
 
-    context "when the redis master goes down" do
-      it "sets the message bus keepalive interval to 0" do
-        expect_master_info
-          .raises(Redis::ConnectionError.new)
-
-        MessageBus.expects(:keepalive_interval=).with(0)
-
-        DiscourseRedis::Connector.new(config).resolve
-
-        execution.stop_other_tasks
-      end
+    after do
+      fallback_handler.master = true
+      MessageBus.keepalive_interval = @original_keepalive_interval
     end
 
-    context "when the redis master comes back up" do
-      before do
-        MessageBus.keepalive_interval = 60
+    describe '#initiate_fallback_to_master' do
+      it 'should return the right value if the master server is still down' do
+        fallback_handler.master = false
+        Redis::Client.any_instance.expects(:call).with([:info]).returns("Some other stuff")
 
-        expect_master_info
-          .raises(Redis::ConnectionError.new)
-
-        DiscourseRedis::Connector.new(config).resolve
-
-        expect_master_info
-          .returns(info_response(['loading', '0'], ['role', 'master']))
-
-        expect_fallback
+        expect(fallback_handler.initiate_fallback_to_master).to eq(false)
+        expect(MessageBus.keepalive_interval).to eq(0)
       end
 
-      it "sets the message bus keepalive interval to its original value" do
-        MessageBus.expects(:keepalive_interval=).with(60)
-      end
+      it 'should fallback to the master server once it is up' do
+        fallback_handler.master = false
+        master_conn = mock('master')
+        slave_conn = mock('slave')
 
-      it "calls clear_readonly! and request_refresh! on Discourse" do
-        Discourse.expects(:clear_readonly!)
-        Discourse.expects(:request_refresh!)
-      end
-    end
-  end
+        Redis::Client.expects(:new)
+          .with(DiscourseRedis.config)
+          .returns(master_conn)
 
-  context "when message bus and main are on different hosts" do
-    use_fake_threads
+        Redis::Client.expects(:new)
+          .with(DiscourseRedis.slave_config)
+          .returns(slave_conn)
 
-    before do
-      # Since config is based on GlobalSetting, we need to fetch it before stubbing
-      conf = config
+        master_conn.expects(:call)
+          .with([:info])
+          .returns("
+            #{DiscourseRedis::FallbackHandler::MASTER_ROLE_STATUS}\r\n
+            #{DiscourseRedis::FallbackHandler::MASTER_LOADED_STATUS}
+          ")
 
-      GlobalSetting.stubs(:redis_config).returns(conf)
+        DiscourseRedis::FallbackHandler::CONNECTION_TYPES.each do |connection_type|
+          slave_conn.expects(:call).with(
+            [:client, [:kill, 'type', connection_type]]
+          )
+        end
 
-      message_bus_config = conf.dup
-      message_bus_config[:port] = message_bus_config[:port].to_i + 1
-      message_bus_config[:slave_port] = message_bus_config[:slave_port].to_i + 1
+        master_conn.expects(:disconnect)
+        slave_conn.expects(:disconnect)
 
-      GlobalSetting.stubs(:message_bus_redis_config).returns(message_bus_config)
-
-      Concurrency::ThreadedExecution.stubs(:new).returns(execution)
-    end
-
-    let(:message_bus_master_config) {
-      GlobalSetting.message_bus_redis_config
-    }
-
-    context "when the message bus master goes down" do
-      before do
-        expect_master_info(message_bus_master_config)
-          .raises(Redis::ConnectionError.new)
-      end
-
-      it "sets the message bus keepalive interval to 0" do
-        MessageBus.expects(:keepalive_interval=).with(0)
-
-        DiscourseRedis::Connector.new(message_bus_master_config).resolve
-
-        execution.stop_other_tasks
-      end
-
-      it "does not call clear_readonly! or request_refresh! on Discourse" do
-        Discourse.expects(:clear_readonly!).never
-        Discourse.expects(:request_refresh!).never
-
-        DiscourseRedis::Connector.new(message_bus_master_config).resolve
-
-        execution.stop_other_tasks
-      end
-    end
-
-    context "when the message bus master comes back up" do
-      before do
-        MessageBus.keepalive_interval = 60
-
-        expect_master_info(message_bus_master_config)
-          .raises(Redis::ConnectionError.new)
-
-        DiscourseRedis::Connector.new(message_bus_master_config).resolve
-
-        expect_master_info(message_bus_master_config)
-          .returns(info_response(['loading', '0'], ['role', 'master']))
-
-        expect_fallback(DiscourseRedis.slave_config(message_bus_master_config))
-      end
-
-      it "sets the message bus keepalive interval to its original value" do
-        MessageBus.expects(:keepalive_interval=).with(60)
-      end
-    end
-
-    context "when the main master goes down" do
-      before do
-        expect_master_info
-          .raises(Redis::ConnectionError.new)
-      end
-
-      it "does not change the message bus keepalive interval" do
-        MessageBus.expects(:keepalive_interval=).never
-
-        DiscourseRedis::Connector.new(config).resolve
-
-        execution.stop_other_tasks
-      end
-    end
-
-    context "when the main master comes back up" do
-      before do
-        expect_master_info
-          .raises(Redis::ConnectionError.new)
-
-        DiscourseRedis::Connector.new(config).resolve
-
-        expect_master_info
-          .returns(info_response(['loading', '0'], ['role', 'master']))
-
-        expect_fallback
-      end
-
-      it "does not change the message bus keepalive interval" do
-        MessageBus.expects(:keepalive_interval=).never
-      end
-
-      it "calls clear_readonly! and request_refresh! on Discourse" do
-        Discourse.expects(:clear_readonly!)
-        Discourse.expects(:request_refresh!)
+        expect(fallback_handler.initiate_fallback_to_master).to eq(true)
+        expect(fallback_handler.master).to eq(true)
+        expect(Discourse.recently_readonly?).to eq(false)
+        expect(MessageBus.keepalive_interval).to eq(-1)
       end
     end
   end
diff --git a/spec/support/concurrency.rb b/spec/support/concurrency.rb
index 062bcab56b5..5d3cd0c87c4 100644
--- a/spec/support/concurrency.rb
+++ b/spec/support/concurrency.rb
@@ -30,7 +30,7 @@ module Concurrency
         end
 
         def choose_with_weights(*options)
-          choose(*options.map(&:first))
+          choose(options.map(&:first))
         end
 
         def dead_end
@@ -147,11 +147,10 @@ module Concurrency
       def initialize(path)
         @path = path
         @tasks = []
-        @time = 0
       end
 
       def yield
-        sleep(0)
+        Fiber.yield
       end
 
       def choose(*options)
@@ -162,86 +161,30 @@ module Concurrency
         @path.choose_with_weights(*options)
       end
 
-      def stop_other_tasks
-        @tasts = @tasks.select! { |task| task[:fiber] == Fiber.current }
-      end
-
-      def sleep(length)
-        Fiber.yield(@time + length)
-      end
-
-      def start_root(&blk)
-        descriptor = {
-          fiber: Fiber.new(&blk),
-          run_at: 0
-        }
-
-        @tasks << descriptor
-      end
-
       def spawn(&blk)
-        descriptor = {
-          fiber: Fiber.new(&blk),
-          run_at: @time
-        }
-
-        @tasks << descriptor
-
-        self.yield
+        @tasks << Fiber.new(&blk)
       end
 
-      def run(sleep_order: false)
+      def run
         until @tasks.empty?
-          descriptor =
-            if sleep_order
-              @tasks.sort_by! { |x| x[:run_at] }
-              run_at = @tasks.first[:run_at]
-              @path.choose(*@tasks.take_while { |x| x[:run_at] == run_at })
-            else
-              @path.choose(*@tasks)
-            end
-
-          @time = [@time, descriptor[:run_at]].max
-          fiber = descriptor[:fiber]
-
-          begin
-            run_at = fiber.resume
-          rescue Exception
-          end
-
-          if fiber.alive?
-            descriptor[:run_at] = run_at
-          else
-            @tasks.delete(descriptor)
+          task = @path.choose(*@tasks)
+          task.resume
+          unless task.alive?
+            @tasks.delete(task)
           end
         end
       end
-
-      def wait_done
-        until @tasks.size == 1
-          self.sleep(1e9)
-        end
-      end
-
-      def new_mutex
-        Mutex.new(self)
-      end
     end
 
-    def run_with_path(path, sleep_order: false)
+    def run_with_path(path)
       execution = Execution.new(path)
-      result = {}
-      execution.start_root {
-        result[:value] = @blk.call(execution)
-      }
-      execution.run(sleep_order: sleep_order)
+      result = @blk.call(execution)
+      execution.run
       result
     end
 
-    def run(sleep_order: false, **opts)
-      Logic.run(**opts) do |path|
-        run_with_path(path, sleep_order: sleep_order)
-      end
+    def run(**opts)
+      Logic.run(**opts, &method(:run_with_path))
     end
   end
 
@@ -307,45 +250,4 @@ module Concurrency
       result
     end
   end
-
-  class Mutex
-    def initialize(execution)
-      @execution = execution
-      @locked_by = nil
-    end
-
-    def lock
-      @execution.yield
-
-      fiber = Fiber.current
-      while true
-        if @locked_by.nil?
-          @locked_by = fiber
-          return
-        elsif @locked_by == fiber
-          raise ThreadError, "deadlock; recursive locking"
-        else
-          @execution.yield
-        end
-      end
-    end
-
-    def unlock
-      @execution.yield
-
-      if @locked_by != Fiber.current
-        raise ThreadError, "Attempt to unlock a mutex which is locked by another thread"
-      end
-      @locked_by = nil
-    end
-
-    def synchronize
-      lock
-      begin
-        yield
-      ensure
-        unlock
-      end
-    end
-  end
 end