WIP: Use NIO.2 WatchService for JRuby

lib/listen/adapter.rb

@@ -4,10 +4,11 @@
 require 'listen/adapter/linux'
 require 'listen/adapter/polling'
 require 'listen/adapter/windows'
+require 'listen/adapter/jruby'
 
 module Listen
   module Adapter
-    OPTIMIZED_ADAPTERS = [Darwin, Linux, BSD, Windows].freeze
+    OPTIMIZED_ADAPTERS = [Darwin, Linux, BSD, Windows, Jruby].freeze
     POLLING_FALLBACK_MESSAGE = 'Listen will be polling for changes.'\
       'Learn more at https://github.com/guard/listen#listen-adapters.'.freeze
 

lib/listen/adapter/jruby.rb

@@ -0,0 +1,55 @@
+module Listen
+  module Adapter
+    # @see https://docs.oracle.com/javase/tutorial/essential/io/notification.html
+    class Jruby < Base
+      def self.usable?
+        RUBY_ENGINE == 'jruby'
+      end
+
+      private
+
+      def _configure(directory, &callback)
+        require 'java'
+        java_import 'java.nio.file.FileSystems'
+        java_import 'java.nio.file.Paths'
+        java_import 'java.nio.file.StandardWatchEventKinds'
+
+        event_kinds = [
+          StandardWatchEventKinds::ENTRY_CREATE,
+          StandardWatchEventKinds::ENTRY_MODIFY,
+          StandardWatchEventKinds::ENTRY_DELETE
+        ]
+
+        @watcher ||= FileSystems.getDefault.newWatchService
+        @keys ||= {}
+        path = Paths.get(directory.to_s)
+        key = path.register(@watcher, *event_kinds)
+        @keys[key] = path
+      end
+
+      def _run
+        loop do
+          key = @watcher.take
+          dir = @keys[key]
+          next if dir.nil?
+          key.pollEvents.each do |event|
+            kind = event.kind
+            next if kind == StandardWatchEventKinds::OVERFLOW
+            name = event.context
+            child = dir.resolve(name)
+            pathname = Pathname.new(child.to_s).dirname
+            _queue_change(:dir, pathname, '.', recursive: true)
+            valid = key.reset
+            unless valid
+              @keys.delete(key)
+              break if @keys.empty?
+            end
+          end
+        end
+      end
+
+      def _process_event(dir, event)
+      end
+    end
+  end
+end

spec/lib/listen/adapter/jruby_spec.rb

@@ -0,0 +1,11 @@
+RSpec.describe Listen::Adapter::Jruby do
+  describe 'class' do
+    subject { described_class }
+
+    if jruby?
+      it { should be_usable }
+    else
+      it { should_not be_usable }
+    end
+  end
+end

spec/lib/listen/adapter_spec.rb

@@ -5,6 +5,7 @@
     allow(Listen::Adapter::Darwin).to receive(:usable?) { false }
     allow(Listen::Adapter::Linux).to receive(:usable?) { false }
     allow(Listen::Adapter::Windows).to receive(:usable?) { false }
+    allow(Listen::Adapter::Jruby).to receive(:usable?) { false }
   end
 
   describe '.select' do
@@ -37,6 +38,12 @@
       expect(klass).to eq Listen::Adapter::Windows
     end
 
+    it 'returns JRuby adapter when usable' do
+      allow(Listen::Adapter::Jruby).to receive(:usable?) { true }
+      klass = Listen::Adapter.select
+      expect(klass).to eq Listen::Adapter::Jruby
+    end
+
     context 'no usable adapters' do
       before { allow(Kernel).to receive(:warn) }
 

spec/support/platform_helper.rb

@@ -13,3 +13,7 @@ def bsd?
 def windows?
   RbConfig::CONFIG['target_os'] =~ /mswin|mingw|cygwin/i
 end
+
+def jruby?
+  RUBY_ENGINE == 'jruby'
+end