Watcher: No need to keep checking mtimes if already stale

Author: jeremy

lib/spring/watcher/polling.rb

@@ -25,10 +25,12 @@ def start
           @poller = Thread.new {
             Thread.current.abort_on_exception = true
 
-            loop do
+            until stale?
               Kernel.sleep latency
               check_stale
             end
+
+            @poller = nil
           }
         end
       end

test/unit/watcher_test.rb

@@ -6,4 +6,48 @@ class PollingWatcherTest < Spring::Test::WatcherTest
   def watcher_class
     Spring::Watcher::Polling
   end
+
+  test "skips staleness checks if already stale" do
+    class << watcher
+      attr_reader :checked_when_stale_count
+      attr_reader :checked_when_not_stale_count
+
+      def check_stale
+        @checked_when_stale_count = 0 unless defined? @checked_when_stale_count
+        @checked_when_not_stale_count = 0 unless defined? @checked_when_not_stale_count
+
+        if stale?
+          @checked_when_stale_count += 1
+        else
+          @checked_when_not_stale_count += 1
+        end
+
+        super
+      end
+    end
+
+    # Track when we're marked as stale.
+    on_stale_count = 0
+    watcher.on_stale { on_stale_count += 1 }
+
+    # Add a file to watch and start polling.
+    file = "#{@dir}/omg"
+    touch file, Time.now - 2.seconds
+    watcher.add file
+    watcher.start
+
+    # First touch bumps mtime and marks as stale.
+    touch file, Time.now - 1.second
+    Timeout.timeout(1) { sleep 0.01 until on_stale_count > 0 }
+    assert_equal 0, watcher.checked_when_stale_count
+    assert_equal 1, watcher.checked_when_not_stale_count
+    assert_equal 1, on_stale_count
+
+    # Second touch skips mtime check because it's already stale.
+    touch file, Time.now
+    sleep 1
+    assert_equal 0, watcher.checked_when_stale_count
+    assert_equal 1, watcher.checked_when_not_stale_count
+    assert_equal 1, on_stale_count
+  end
 end