Merge pull request rails#51030 from searls/queue-approach-to-preview-image-race-condition

Fixes race condition for multiple preprocessed video variants

Author: rafaelfranca

activestorage/app/jobs/active_storage/preview_image_job.rb

@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class ActiveStorage::PreviewImageJob < ActiveStorage::BaseJob
+  queue_as { ActiveStorage.queues[:preview_image] }
+
+  discard_on ActiveRecord::RecordNotFound, ActiveStorage::UnrepresentableError
+  retry_on ActiveStorage::IntegrityError, attempts: 10, wait: :polynomially_longer
+
+  def perform(blob, variations)
+    blob.preview({}).processed
+
+    variations.each do |transformations|
+      blob.preprocessed(transformations)
+    end
+  end
+end

activestorage/app/models/active_storage/attachment.rb

@@ -132,8 +132,18 @@ def mirror_blob_later
     end
 
     def transform_variants_later
-      named_variants.each do |_name, named_variant|
-        blob.preprocessed(named_variant.transformations) if named_variant.preprocessed?(record)
+      preprocessed_variations = named_variants.filter_map { |_name, named_variant|
+        if named_variant.preprocessed?(record)
+          named_variant.transformations
+        end
+      }
+
+      if blob.preview_image_needed_before_processing_variants?
+        blob.create_preview_image_later(preprocessed_variations)
+      else
+        preprocessed_variations.each do |transformations|
+          blob.preprocessed(transformations)
+        end
       end
     end
 

activestorage/app/models/active_storage/blob/representable.rb

@@ -98,6 +98,14 @@ def representable?
     variable? || previewable?
   end
 
+  def preview_image_needed_before_processing_variants?
+    previewable? && !preview_image.attached?
+  end
+
+  def create_preview_image_later(variations) # :nodoc:
+    ActiveStorage::PreviewImageJob.perform_later(self, variations) if representable?
+  end
+
   def preprocessed(transformations) # :nodoc:
     ActiveStorage::TransformJob.perform_later(self, transformations) if representable?
   end