Namespace configuration env vars with backwards compatibility

Namespace all configuration variables used by Delayed::Job under the
`DELAYED_JOB_`-prefix. This will allow developers to easily figure out
what the env var is used for at a glance and prevent collisions with
other libraries using similarly named variable names.

Allow non-namespaced configuration variables as a fallback, but with a
deprecation warning.

See #1028

CHANGELOG.md

@@ -1,3 +1,8 @@
+master (unreleased)
+===================
+* Allow namespaced configuration env vars with `DELAYED_JOB_`-prefix
+* Deprecate non-namespaced configuration env vars
+
 4.1.5 - 2018-04-13
 =================
 * Allow Rails 5.2

README.md

@@ -265,10 +265,11 @@ cancel the rake task with `CTRL-C`.
 
 If you want to just run all available jobs and exit you can use `rake jobs:workoff`
 
-Work off queues by setting the `QUEUE` or `QUEUES` environment variable.
+Work off queues by setting the `DELAYED_JOB_QUEUE` or `DELAYED_JOB_QUEUES`
+environment variable.
 
-    QUEUE=tracking rake jobs:work
-    QUEUES=mailers,tasks rake jobs:work
+    DELAYED_JOB_QUEUE=tracking rake jobs:work
+    DELAYED_JOB_QUEUES=mailers,tasks rake jobs:work
 
 Restarting delayed_job
 ======================

lib/delayed/tasks.rb

@@ -15,15 +15,25 @@
   end
 
   task :environment_options => :environment do
+    def read_env(name)
+      return ::ENV[name] if ::ENV.key?(name)
+
+      deprecated_name = name[/DELAYED_JOB_(.+)/, 1]
+      if ::ENV.key?(deprecated_name)
+        warn "[DEPRECATION] '#{deprecated_name}' for configuration is deprecated. Use '#{name}'"
+        ::ENV[deprecated_name]
+      end
+    end
+
     @worker_options = {
-      :min_priority => ENV['MIN_PRIORITY'],
-      :max_priority => ENV['MAX_PRIORITY'],
-      :queues => (ENV['QUEUES'] || ENV['QUEUE'] || '').split(','),
-      :quiet => ENV['QUIET']
+      :min_priority => read_env('DELAYED_JOB_MIN_PRIORITY'),
+      :max_priority => read_env('DELAYED_JOB_MAX_PRIORITY'),
+      :queues => (read_env('DELAYED_JOB_QUEUES') || read_env('DELAYED_JOB_QUEUE') || '').split(','),
+      :quiet => read_env('DELAYED_JOB_QUIET')
     }
 
-    @worker_options[:sleep_delay] = ENV['SLEEP_DELAY'].to_i if ENV['SLEEP_DELAY']
-    @worker_options[:read_ahead] = ENV['READ_AHEAD'].to_i if ENV['READ_AHEAD']
+    @worker_options[:sleep_delay] = read_env('DELAYED_JOB_SLEEP_DELAY').to_i if read_env('DELAYED_JOB_SLEEP_DELAY')
+    @worker_options[:read_ahead] = read_env('DELAYED_JOB_READ_AHEAD').to_i if read_env('DELAYED_JOB_READ_AHEAD')
   end
 
   desc "Exit with error status if any jobs older than max_age seconds haven't been attempted yet."