Rework `Sidekiq::JobsThreads` into `Monitor`

This makes:
- very shallow `Middleware::Monitor` to only request tracking
  of sidekiq jobs,
- `SidekiqStatus::Monitor` to be responsible to maintain persistent
  connection to receive messages,
- `SidekiqStatus::Monitor` to always use structured logging
  and instance variables

config/initializers/sidekiq.rb

@@ -33,7 +33,7 @@ Sidekiq.configure_server do |config|
   config.redis = queues_config_hash
 
   config.server_middleware do |chain|
-    chain.add Gitlab::SidekiqMiddleware::JobsThreads unless ENV['DISABLE_SIDEKIQ_INTERRUPT_RUNNING_JOBS']
+    chain.add Gitlab::SidekiqMiddleware::Monitor
     chain.add Gitlab::SidekiqMiddleware::Metrics if Settings.monitoring.sidekiq_exporter
     chain.add Gitlab::SidekiqMiddleware::ArgumentsLogger if ENV['SIDEKIQ_LOG_ARGUMENTS'] && !enable_json_logs
     chain.add Gitlab::SidekiqMiddleware::MemoryKiller if ENV['SIDEKIQ_MEMORY_KILLER_MAX_RSS']
@@ -59,7 +59,9 @@ Sidekiq.configure_server do |config|
     # Sidekiq (e.g. in an initializer).
     ActiveRecord::Base.clear_all_connections!
 
-    Gitlab::SidekiqStatus::Monitor.instance.start unless ENV['DISABLE_SIDEKIQ_INTERRUPT_RUNNING_JOBS']
+    if ENV.fetch("SIDEKIQ_MONITOR_WORKER", 0).to_i.nonzero?
+      Gitlab::SidekiqMonitor.instance.start
+    end
   end
 
   if enable_reliable_fetch?

doc/administration/troubleshooting/sidekiq.md

@@ -169,3 +169,121 @@ The PostgreSQL wiki has details on the query you can run to see blocking
 queries. The query is different based on PostgreSQL version. See
 [Lock Monitoring](https://wiki.postgresql.org/wiki/Lock_Monitoring) for
 the query details.
+
+## Managing Sidekiq queues
+
+It is possible to use [Sidekiq API](https://github.com/mperham/sidekiq/wiki/API)
+to perform a number of troubleshoting on Sidekiq.
+
+These are the administrative commands and it should only be used if currently
+admin interface is not suitable due to scale of installation.
+
+All this commands should be run using `gitlab-rails console`.
+
+### View the queue size
+
+```ruby
+Sidekiq::Queue.new("pipeline_processing:build_queue").size
+```
+
+### Enumerate all enqueued jobs
+
+```ruby
+queue = Sidekiq::Queue.new("chaos:chaos_sleep")
+queue.each do |job|
+  # job.klass # => 'MyWorker'
+  # job.args # => [1, 2, 3]
+  # job.jid # => jid
+  # job.queue # => chaos:chaos_sleep
+  # job["retry"] # => 3
+  # job.item # => {
+  #   "class"=>"Chaos::SleepWorker",
+  #   "args"=>[1000],
+  #   "retry"=>3,
+  #   "queue"=>"chaos:chaos_sleep",
+  #   "backtrace"=>true,
+  #   "queue_namespace"=>"chaos",
+  #   "jid"=>"39bc482b823cceaf07213523",
+  #   "created_at"=>1566317076.266069,
+  #   "correlation_id"=>"c323b832-a857-4858-b695-672de6f0e1af",
+  #   "enqueued_at"=>1566317076.26761},
+  # }
+
+  # job.delete if job.jid == 'abcdef1234567890'
+end
+```
+
+### Enumerate currently running jobs
+
+```ruby
+workers = Sidekiq::Workers.new
+workers.each do |process_id, thread_id, work|
+  # process_id is a unique identifier per Sidekiq process
+  # thread_id is a unique identifier per thread
+  # work is a Hash which looks like:
+  # {"queue"=>"chaos:chaos_sleep",
+  #  "payload"=>
+  #  { "class"=>"Chaos::SleepWorker",
+  #    "args"=>[1000],
+  #    "retry"=>3,
+  #    "queue"=>"chaos:chaos_sleep",
+  #    "backtrace"=>true,
+  #    "queue_namespace"=>"chaos",
+  #    "jid"=>"b2a31e3eac7b1a99ff235869",
+  #    "created_at"=>1566316974.9215662,
+  #    "correlation_id"=>"e484fb26-7576-45f9-bf21-b99389e1c53c",
+  #    "enqueued_at"=>1566316974.9229589},
+  #  "run_at"=>1566316974}],
+end
+```
+
+### Remove sidekiq jobs for given parameters (destructive)
+
+```ruby
+# for jobs like this:
+# RepositoryImportWorker.new.perform_async(100)
+id_list = [100]
+
+queue = Sidekiq::Queue.new('repository_import')
+queue.each do |job|
+  job.delete if id_list.include?(job.args[0])
+end
+```
+
+### Remove specific job ID (destructive)
+
+```ruby
+queue = Sidekiq::Queue.new('repository_import')
+queue.each do |job|
+  job.delete if job.jid == 'my-job-id'
+end
+```
+
+## Canceling running jobs (destructive)
+
+> Introduced in GitLab 12.3.
+
+This is highly risky operation and use it as last resort.
+Doing that might result in data corruption, as the job
+is interrupted mid-execution and it is not guaranteed
+that proper rollback of transactions is implemented.
+
+```ruby
+Gitlab::SidekiqMonitor.cancel_job('job-id')
+```
+
+> This requires the Sidekiq to be run with `SIDEKIQ_MONITOR_WORKER=1`
+> environment variable.
+
+To perform of the interrupt we use `Thread.raise` which
+has number of drawbacks, as mentioned in [Why Ruby’s Timeout is dangerous (and Thread.raise is terrifying)](https://jvns.ca/blog/2015/11/27/why-rubys-timeout-is-dangerous-and-thread-dot-raise-is-terrifying/):
+
+> This is where the implications get interesting, and terrifying. This means that an exception can get raised:
+>
+> * during a network request (ok, as long as the surrounding code is prepared to catch Timeout::Error)
+> * during the cleanup for the network request
+> * during a rescue block
+> * while creating an object to save to the database afterwards
+> * in any of your code, regardless of whether it could have possibly raised an exception before
+>
+> Nobody writes code to defend against an exception being raised on literally any line. That’s not even possible. So Thread.raise is  basically like a sneak attack on your code that could result in almost anything. It would probably be okay if it were pure-functional code that did not modify any state. But this is Ruby, so that’s unlikely :)

lib/gitlab/sidekiq_middleware/jobs_threads.rb

-# frozen_string_literal: true
-
-module Gitlab
-  module SidekiqMiddleware
-    class JobsThreads
-      @@jobs = {} # rubocop:disable Style/ClassVars
-      MUTEX = Mutex.new
-
-      def call(worker, job, queue)
-        jid = job['jid']
-
-        MUTEX.synchronize do
-          @@jobs[jid] = Thread.current
-        end
-
-        return if self.class.cancelled?(jid)
-
-        yield
-      ensure
-        MUTEX.synchronize do
-          @@jobs.delete(jid)
-        end
-      end
-
-      def self.interrupt(jid)
-        MUTEX.synchronize do
-          thread = @@jobs[jid]
-          break unless thread
-
-          thread.raise(Interrupt)
-          thread
-        end
-      end
-
-      def self.cancelled?(jid)
-        Sidekiq.redis {|c| c.exists("cancelled-#{jid}") }
-      end
-
-      def self.mark_job_as_cancelled(jid)
-        Sidekiq.redis {|c| c.setex("cancelled-#{jid}", 86400, 1) }
-        "Marked job as cancelled(if Sidekiq retry within 24 hours, the job will be skipped as `processed`). Jid: #{jid}"
-      end
-
-      def self.jobs
-        @@jobs
-      end
-    end
-  end
-end

lib/gitlab/sidekiq_middleware/monitor.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module SidekiqMiddleware
+    class Monitor
+      def call(worker, job, queue)
+        Gitlab::SidekiqMonitor.instance.within_job(job['jid'], queue) do
+          yield
+        end
+      end
+    end
+  end
+end

lib/gitlab/sidekiq_monitor.rb

+# frozen_string_literal: true
+
+module Gitlab
+  class SidekiqMonitor < Daemon
+    include ::Gitlab::Utils::StrongMemoize
+
+    NOTIFICATION_CHANNEL = 'sidekiq:cancel:notifications'.freeze
+    CANCEL_DEADLINE = 24.hours.seconds
+
+    # We use exception derived from `Exception`
+    # to consider this as an very low-level exception
+    # that should not be caught by application
+    CancelledError = Class.new(Exception) # rubocop:disable Lint/InheritException
+
+    attr_reader :jobs_thread
+    attr_reader :jobs_mutex
+
+    def initialize
+      super
+
+      @jobs_thread = {}
+      @jobs_mutex = Mutex.new
+    end
+
+    def within_job(jid, queue)
+      jobs_mutex.synchronize do
+        jobs_thread[jid] = Thread.current
+      end
+
+      if cancelled?(jid)
+        Sidekiq.logger.warn(
+          class: self.class,
+          action: 'run',
+          queue: queue,
+          jid: jid,
+          canceled: true)
+        raise CancelledError
+      end
+
+      yield
+    ensure
+      jobs_mutex.synchronize do
+        jobs_thread.delete(jid)
+      end
+    end
+
+    def start_working
+      Sidekiq.logger.info(
+        class: self.class,
+        action: 'start',
+        message: 'Starting Monitor Daemon')
+
+      ::Gitlab::Redis::SharedState.with do |redis|
+        redis.subscribe(NOTIFICATION_CHANNEL) do |on|
+          on.message do |channel, message|
+            process_message(message)
+          end
+        end
+      end
+
+      Sidekiq.logger.warn(
+        class: self.class,
+        action: 'stop',
+        message: 'Stopping Monitor Daemon')
+    rescue Exception => e # rubocop:disable Lint/RescueException
+      Sidekiq.logger.warn(
+        class: self.class,
+        action: 'exception',
+        message: e.message)
+      raise e
+    end
+
+    def self.cancel_job(jid)
+      payload = {
+        action: 'cancel',
+        jid: jid
+      }.to_json
+
+      ::Gitlab::Redis::SharedState.with do |redis|
+        redis.setex(cancel_job_key(jid), CANCEL_DEADLINE, 1)
+        redis.publish(NOTIFICATION_CHANNEL, payload)
+      end
+    end
+
+    private
+
+    def process_message(message)
+      Sidekiq.logger.info(
+        class: self.class,
+        channel: NOTIFICATION_CHANNEL,
+        message: 'Received payload on channel',
+        payload: message)
+
+      message = safe_parse(message)
+      return unless message
+
+      case message['action']
+      when 'cancel'
+        process_job_cancel(message['jid'])
+      else
+        # unknown message
+      end
+    end
+
+    def safe_parse(message)
+      JSON.parse(message)
+    rescue JSON::ParserError
+    end
+
+    def process_job_cancel(jid)
+      return unless jid
+
+      # since this might take time, process cancel in a new thread
+      Thread.new do
+        find_thread(jid) do |thread|
+          next unless thread
+
+          Sidekiq.logger.warn(
+            class: self.class,
+            action: 'cancel',
+            message: 'Canceling thread with CancelledError',
+            jid: jid,
+            thread_id: thread.object_id)
+
+          thread&.raise(CancelledError)
+        end
+      end
+    end
+
+    # This method needs to be thread-safe
+    # This is why it passes thread in block,
+    # to ensure that we do process this thread
+    def find_thread(jid)
+      return unless jid
+
+      jobs_mutex.synchronize do
+        thread = jobs_thread[jid]
+        yield(thread)
+        thread
+      end
+    end
+
+    def cancelled?(jid)
+      ::Gitlab::Redis::SharedState.with do |redis|
+        redis.exists(self.class.cancel_job_key(jid))
+      end
+    end
+
+    def self.cancel_job_key(jid)
+      "sidekiq:cancel:#{jid}"
+    end
+  end
+end

lib/gitlab/sidekiq_status/monitor.rb

-# frozen_string_literal: true
-
-module Gitlab
-  module SidekiqStatus
-    class Monitor < Daemon
-      include ::Gitlab::Utils::StrongMemoize
-
-      NOTIFICATION_CHANNEL = 'sidekiq:cancel:notifications'.freeze
-
-      def start_working
-        Sidekiq.logger.info "Watching sidekiq monitor"
-
-        ::Gitlab::Redis::SharedState.with do |redis|
-          redis.subscribe(NOTIFICATION_CHANNEL) do |on|
-            on.message do |channel, message|
-              Sidekiq.logger.info "Received #{message} on #{channel}..."
-              execute_job_cancel(message)
-            end
-          end
-        end
-      end
-
-      def self.cancel_job(jid)
-        Gitlab::Redis::SharedState.with do |redis|
-          redis.publish(NOTIFICATION_CHANNEL, jid)
-          "Notification sent. Job should be cancelled soon. Check log to confirm. Jid: #{jid}"
-        end
-      end
-
-      private
-
-      def execute_job_cancel(jid)
-        Gitlab::SidekiqMiddleware::JobsThreads.mark_job_as_cancelled(jid)
-
-        thread = Gitlab::SidekiqMiddleware::JobsThreads
-          .interrupt(jid)
-
-        if thread
-          Sidekiq.logger.info "Interrupted thread: #{thread} for #{jid}."
-        else
-          Sidekiq.logger.info "Did not find thread for #{jid}."
-        end
-      end
-    end
-  end
-end

spec/lib/gitlab/sidekiq_middleware/jobs_threads_spec.rb

-require 'spec_helper'
-
-describe Gitlab::SidekiqMiddleware::JobsThreads do
-  subject { described_class.new }
-
-  let(:worker) { double(:worker, class: Chaos::SleepWorker) }
-  let(:jid) { '581f90fbd2f24deabcbde2f9' }
-  let(:job) { { 'jid' => jid } }
-  let(:jid_thread) { '684f90fbd2f24deabcbde2f9' }
-  let(:job_thread) { { 'jid' => jid_thread } }
-  let(:queue) { 'test_queue' }
-  let(:mark_job_as_cancelled) { Sidekiq.redis {|c| c.setex("cancelled-#{jid}", 2, 1) } }
-
-  def run_job
-    subject.call(worker, job, queue) do
-      sleep 2
-      "mock return from yield"
-    end
-  end
-
-  def run_job_thread
-    Thread.new do
-      subject.call(worker, job_thread, queue) do
-        sleep 3
-        "mock return from yield"
-      end
-    end
-  end
-
-  describe '.call' do
-    context 'by default' do
-      it 'return from yield' do
-        expect(run_job).to eq("mock return from yield")
-      end
-    end
-
-    context 'when job is marked as cancelled' do
-      before do
-        mark_job_as_cancelled
-      end
-
-      it 'return directly' do
-        expect(run_job).to be_nil
-      end
-    end
-  end
-
-  describe '.self.interrupt' do
-    before do
-      run_job_thread
-      sleep 1
-    end
-
-    it 'interrupt the job with correct jid' do
-      expect(described_class.jobs[jid_thread]).to receive(:raise).with(Interrupt)
-      expect(described_class.interrupt jid_thread).to eq(described_class.jobs[jid_thread])
-    end
-
-    it 'do nothing with wrong jid' do
-      expect(described_class.jobs[jid_thread]).not_to receive(:raise)
-      expect(described_class.interrupt 'wrong_jid').to be_nil
-    end
-  end
-
-  describe '.self.cancelled?' do
-    it 'return true when job is marked as cancelled' do
-      mark_job_as_cancelled
-      expect(described_class.cancelled? jid).to be true
-    end
-
-    it 'return false when job is not marked as cancelled' do
-      expect(described_class.cancelled? 'non-exists-jid').to be false
-    end
-  end
-
-  describe '.self.mark_job_as_cancelled' do
-    it 'set Redis key' do
-      described_class.mark_job_as_cancelled('jid_123')
-
-      expect(described_class.cancelled? 'jid_123').to be true
-    end
-  end
-end

spec/lib/gitlab/sidekiq_middleware/monitor_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::SidekiqMiddleware::Monitor do
+  let(:monitor) { described_class.new }
+
+  describe '#call' do
+    let(:worker) { double }
+    let(:job) { { 'jid' => 'job-id' } }
+    let(:queue) { 'my-queue' }
+
+    it 'calls SidekiqMonitor' do
+      expect(Gitlab::SidekiqMonitor.instance).to receive(:within_job)
+        .with('job-id', 'my-queue')
+        .and_call_original
+
+      expect { |blk| monitor.call(worker, job, queue, &blk) }.to yield_control
+    end
+
+    it 'passthroughs the return value' do
+      result = monitor.call(worker, job, queue) do
+        'value'
+      end
+
+      expect(result).to eq('value')
+    end
+  end
+end

spec/lib/gitlab/sidekiq_monitor_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::SidekiqMonitor do
+  let(:monitor) { described_class.new }
+
+  describe '#within_job' do
+    it 'tracks thread' do
+      blk = proc do
+        expect(monitor.jobs_thread['jid']).not_to be_nil
+
+        "OK"
+      end
+
+      expect(monitor.within_job('jid', 'queue', &blk)).to eq("OK")
+    end
+
+    context 'when job is canceled' do
+      let(:jid) { SecureRandom.hex }
+
+      before do
+        described_class.cancel_job(jid)
+      end
+
+      it 'does not execute a block' do
+        expect do |blk|
+          monitor.within_job(jid, 'queue', &blk)
+        rescue described_class::CancelledError
+        end.not_to yield_control
+      end
+
+      it 'raises exception' do
+        expect { monitor.within_job(jid, 'queue') }.to raise_error(described_class::CancelledError)
+      end
+    end
+  end
+
+  describe '#start_working' do
+    subject { monitor.start_working }
+
+    context 'when structured logging is used' do
+      before do
+        allow_any_instance_of(::Redis).to receive(:subscribe)
+      end
+
+      it 'logs start message' do
+        expect(Sidekiq.logger).to receive(:info)
+          .with(
+            class: described_class,
+            action: 'start',
+            message: 'Starting Monitor Daemon')
+
+        subject
+      end
+
+      it 'logs stop message' do
+        expect(Sidekiq.logger).to receive(:warn)
+          .with(
+            class: described_class,
+            action: 'stop',
+            message: 'Stopping Monitor Daemon')
+
+        subject
+      end
+
+      it 'logs exception message' do
+        expect(Sidekiq.logger).to receive(:warn)
+          .with(
+            class: described_class,
+            action: 'exception',
+            message: 'My Exception')
+
+        expect(::Gitlab::Redis::SharedState).to receive(:with)
+          .and_raise(Exception, 'My Exception')
+
+        expect { subject }.to raise_error(Exception, 'My Exception')
+      end
+    end
+
+    context 'when message is published' do
+      let(:subscribed) { double }
+
+      before do
+        expect_any_instance_of(::Redis).to receive(:subscribe)
+          .and_yield(subscribed)
+
+        expect(subscribed).to receive(:message)
+          .and_yield(
+            described_class::NOTIFICATION_CHANNEL,
+            payload
+          )
+
+        expect(Sidekiq.logger).to receive(:info)
+          .with(
+            class: described_class,
+            action: 'start',
+            message: 'Starting Monitor Daemon')
+
+        expect(Sidekiq.logger).to receive(:info)
+          .with(
+            class: described_class,
+            channel: described_class::NOTIFICATION_CHANNEL,
+            message: 'Received payload on channel',
+            payload: payload
+          )
+      end
+
+      context 'and message is valid' do
+        let(:payload) { '{"action":"cancel","jid":"my-jid"}' }
+
+        it 'processes cancel' do
+          expect(monitor).to receive(:process_job_cancel).with('my-jid')
+
+          subject
+        end
+      end
+
+      context 'and message is not valid json' do
+        let(:payload) { '{"action"}' }
+
+        it 'skips processing' do
+          expect(monitor).not_to receive(:process_job_cancel)
+
+          subject
+        end
+      end
+    end
+  end
+
+  describe '#process_job_cancel' do
+    subject { monitor.send(:process_job_cancel, jid) }
+
+    context 'when jid is missing' do
+      let(:jid) { nil }
+
+      it 'does not run thread' do
+        expect(subject).to be_nil
+      end
+    end
+
+    context 'when jid is provided' do
+      let(:jid) { 'my-jid' }
+
+      context 'when jid is not found' do
+        it 'does not log cancellation message' do
+          expect(Sidekiq.logger).not_to receive(:warn)
+          expect(subject).to be_a(Thread)
+
+          subject.join
+        end
+      end
+
+      context 'when jid is found' do
+        let(:thread) { Thread.new { sleep 1000 } }
+
+        before do
+          monitor.jobs_thread[jid] = thread
+        end
+
+        it 'does log cancellation message' do
+          expect(Sidekiq.logger).to receive(:warn)
+            .with(
+              class: described_class,
+              action: 'cancel',
+              message: 'Canceling thread with CancelledError',
+              jid: 'my-jid',
+              thread_id: thread.object_id)
+
+          expect(subject).to be_a(Thread)
+
+          subject.join
+        end
+
+        it 'does cancel the thread' do
+          expect(subject).to be_a(Thread)
+
+          subject.join
+
+          expect(thread).not_to be_alive
+          expect { thread.value }.to raise_error(described_class::CancelledError)
+        end
+      end
+    end
+  end
+
+  describe '.cancel_job' do
+    subject { described_class.cancel_job('my-jid') }
+
+    it 'sets a redis key' do
+      expect_any_instance_of(::Redis).to receive(:setex)
+        .with('sidekiq:cancel:my-jid', anything, 1)
+
+      subject
+    end
+
+    it 'notifies all workers' do
+      payload = '{"action":"cancel","jid":"my-jid"}'
+
+      expect_any_instance_of(::Redis).to receive(:publish)
+        .with('sidekiq:cancel:notifications', payload)
+
+      subject
+    end
+  end
+end