Explicitly add redlock dependency. Require redlock

Gemfile

@@ -56,6 +56,7 @@ gem 'rails', '~> 6.0'
 gem 'rdf', git: 'https://github.com/ruby-rdf/rdf.git', branch: '3.2.11-patch'
 # Use Redis adapter to run Action Cable in production
 gem 'redis', '~> 4.5.0'
+gem 'redlock' # version determined by hyrax
 gem 'riiif', '~> 2.5.0'
 gem 'roo', '~>2.9.0'
 gem 'rsolr', '~> 2.5.0'

Gemfile.lock

@@ -1130,6 +1130,7 @@ DEPENDENCIES
   rails (~> 6.0)
   rdf!
   redis (~> 4.5.0)
+  redlock
   riiif (~> 2.5.0)
   roo (~> 2.9.0)
   rsolr (~> 2.5.0)

app/overrides/lib/hydra/derivatives/processors/document_override.rb

@@ -1,12 +1,15 @@
 # frozen_string_literal: true
 # [hyc-override] https://github.com/samvera/hydra-derivatives/blob/v3.8.0/lib/hydra/derivatives/processors/document.rb
+require 'redlock'
+
 class SofficeTimeoutError < StandardError; end
 
 Hydra::Derivatives::Processors::Document.class_eval do
+  # [hyc-override] Use Redlock to manage soffice process lock
   LOCK_KEY = "soffice:document_conversion"
   LOCK_TIMEOUT = 6 * 60 * 1000
   JOB_TIMEOUT_SECONDS = 30
-  LOCK_MANAGER = Redlock::Client.new([ENV['REDIS_URL']])
+  LOCK_MANAGER = Redlock::Client.new([Redis.current])
 
   # [hyc-override] Trigger kill if soffice process takes too long, and throw a non-retry error if that happens
   def self.encode(path, format, outdir, timeout = JOB_TIMEOUT_SECONDS)
@@ -37,6 +40,7 @@ def self.encode(path, format, outdir, timeout = JOB_TIMEOUT_SECONDS)
   # TODO: file_suffix and options are passed from ShellBasedProcessor.process but are not needed.
   #       A refactor could simplify this.
   def encode_file(_file_suffix, _options = {})
+    # [hyc-override] Use Redlock to manage soffice process lock, since only one soffice process can run at a time
     LOCK_MANAGER.lock(LOCK_KEY, LOCK_TIMEOUT) do |locked|
       if locked
         convert_to_format