Enable per job class max_job_runtime

This allows incremental adoption of the setting, without applying the setting
globally. Alternatively, it allows applications to set a conservative global
setting, and a more aggressive setting per jobs.

In order to prevent rogue jobs from causing trouble, the per-job override can
only be set to a value less than the inherited value.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - [241](https://github.com/Shopify/job-iteration/pull/241) - Require Ruby 2.7+, dropping 2.6 support
 - [241](https://github.com/Shopify/job-iteration/pull/241) - Require Rails 6.0+, dropping 5.2 support
+- [240](https://github.com/Shopify/job-iteration/pull/240) - Allow setting inheritable per-job `max_job_runtime`
 
 ## v1.3.6 (Mar 9, 2022)
 

guides/best-practices.md

@@ -66,3 +66,18 @@ JobIteration.max_job_runtime = 5.minutes # nil by default
 ```
 
 Use this accessor to tweak how often you'd like the job to interrupt itself.
+
+### Per job max job runtime
+
+For more granular control, `max_job_runtime` can be set **per-job class**. This allows both incremental adoption, as well as using a conservative global setting, and an aggressive setting on a per-job basis.
+
+```ruby
+class MyJob < ApplicationJob
+  include JobIteration::Iteration
+
+  self.max_job_runtime = 3.minutes
+
+  # ...
+```
+
+This setting will be inherited by any child classes, although it can be further overridden. Note that no class can **increase** the `max_job_runtime` it has inherited; it can only be **decreased**.

lib/job-iteration/iteration.rb

@@ -39,6 +39,27 @@ def inspected_cursor
       define_callbacks :start
       define_callbacks :shutdown
       define_callbacks :complete
+
+      class_attribute :max_job_runtime, instance_writer: false, instance_predicate: false, default: JobIteration.max_job_runtime
+
+      singleton_class.prepend PrependedClassMethods
+    end
+
+    module PrependedClassMethods
+      def max_job_runtime=(new)
+        existing = max_job_runtime
+
+        if existing && (!new || new > existing)
+          existing_label = existing.inspect
+          new_label = new ? new.inspect : "#{new.inspect} (no limit)"
+          raise(
+            ArgumentError,
+            "max_job_runtime may only decrease; #{self} tried to increase it from #{existing_label} to #{new_label}",
+          )
+        end
+
+        super
+      end
     end
 
     module ClassMethods
@@ -262,7 +283,7 @@ def output_interrupt_summary
     end
 
     def job_should_exit?
-      if ::JobIteration.max_job_runtime && start_time && (Time.now.utc - start_time) > ::JobIteration.max_job_runtime
+      if max_job_runtime && start_time && (Time.now.utc - start_time) > max_job_runtime
         return true
       end
 

test/unit/iteration_test.rb

@@ -251,6 +251,75 @@ def test_global_max_job_runtime
     end
   end
 
+  def test_per_class_max_job_runtime_with_no_global_set
+    freeze_time
+    with_global_max_job_runtime(nil) do
+      parent = build_slow_job_class(iterations: 3, iteration_duration: 30.seconds)
+      child = Class.new(parent) do
+        self.max_job_runtime = 1.minute
+      end
+
+      parent.perform_now
+      assert_no_enqueued_jobs
+
+      child.perform_now
+      assert_partially_completed_job(cursor_position: 2)
+    end
+  end
+
+  def test_per_class_max_job_runtime_with_global_set
+    freeze_time
+    with_global_max_job_runtime(1.minute) do
+      parent = build_slow_job_class(iterations: 3, iteration_duration: 30.seconds)
+      child = Class.new(parent) do
+        self.max_job_runtime = 30.seconds
+      end
+
+      parent.perform_now
+      assert_partially_completed_job(cursor_position: 2)
+      clear_enqueued_jobs
+
+      child.perform_now
+      assert_partially_completed_job(cursor_position: 1)
+    end
+  end
+
+  def test_max_job_runtime_cannot_be_higher_than_global
+    with_global_max_job_runtime(30.seconds) do
+      klass = Class.new(ActiveJob::Base) do
+        include JobIteration::Iteration
+      end
+
+      error = assert_raises(ArgumentError) do
+        klass.max_job_runtime = 1.minute
+      end
+
+      assert_equal(
+        "max_job_runtime may only decrease; #{klass} tried to increase it from 30 seconds to 1 minute",
+        error.message,
+      )
+    end
+  end
+
+  def test_max_job_runtime_cannot_be_higher_than_parent
+    with_global_max_job_runtime(1.minute) do
+      parent = Class.new(ActiveJob::Base) do
+        include JobIteration::Iteration
+        self.max_job_runtime = 30.seconds
+      end
+      child = Class.new(parent)
+
+      error = assert_raises(ArgumentError) do
+        child.max_job_runtime = 45.seconds
+      end
+
+      assert_equal(
+        "max_job_runtime may only decrease; #{child} tried to increase it from 30 seconds to 45 seconds",
+        error.message,
+      )
+    end
+  end
+
   private
 
   # Allows building job classes that read max_job_runtime during the test,