option for writing to all nodes in a multicache ring

refs CNVS-30659

Change-Id: I2fcc74e9a4bede89adb1122bcea8fea7925805f2
Reviewed-on: https://gerrit.instructure.com/86735
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

lib/multi_cache.rb

@@ -33,9 +33,26 @@ class MultiCache < ActiveSupport::Cache::Store
 
   def fetch(key, options = nil, &block)
     options ||= {}
-    # this makes the node "sticky" for read/write
-    options[:node] = @ring[rand(@ring.length)]
-    super(key, options, &block)
+    # an option to allow populating all nodes in the ring with the
+    # same data
+    if options[:node] == :all
+      calculated_value = nil
+      did_calculate = false
+      result = nil
+      @ring.each do |node|
+        options[:node] = node
+        result = super(key, options) do
+          calculated_value = yield unless did_calculate
+          did_calculate = true
+          calculated_value
+        end
+      end
+      result
+    else
+      # this makes the node "sticky" for read/write
+      options[:node] = @ring[rand(@ring.length)]
+      super(key, options, &block)
+    end
   end
 
   # for compatibility

spec/lib/multi_cache_spec.rb

@@ -62,4 +62,17 @@ describe MultiCache do
     store = MultiCache.new(ring)
     expect(store.delete('key')).to eq true
   end
+
+  it 'allows writing to all nodes' do
+    ring = [mock, mock]
+    ring[0].expects(:get).once
+    ring[0].expects(:set).once
+    ring[1].expects(:get).once
+    ring[1].expects(:set).once
+
+    store = MultiCache.new(ring)
+    generated = 0
+    store.fetch('key', node: :all) { generated += 1 }
+    expect(generated).to eq 1
+  end
 end