Alter "wait for changes" algorithm to wait for incoming changes to ac…

…cumulate before calling block. Fixes guard#202

The new algorithm is (pseudocode):

      loop
        begin
          sleep options[:wait_for_delay] # wait for changes to accumulate
          new_changes = _pop_changes
          changes += new_changes
        end until new_changes.empty?
        unless changes.empty?
          block.call(changes)
        end
      end

Note that the "sleep" happens both before and after any callback, so the
value of wait_for_delay is effectively doubled. This also means that if
the filesystem is constantly changing, the callback will never happen...
maybe we should check for this and bail out after, say, 10 seconds even
if new changes keep on coming.

lib/listen/listener.rb

@@ -138,24 +138,33 @@ def _wait_for_changes
       loop do
         break if @stopping
 
-        changes = _pop_changes
-        unless changes.all? { |_,v| v.empty? }
-          block.call(changes[:modified], changes[:added], changes[:removed])
+        changes = []
+        begin
+          sleep options[:wait_for_delay] # wait for changes to accumulate
+          new_changes = _pop_changes
+          changes += new_changes
+        end until new_changes.empty?
+        unless changes.empty?
+          hash = _smoosh_changes changes
+          block.call(hash[:modified], hash[:added], hash[:removed])
         end
-        sleep options[:wait_for_delay]
       end
     rescue => ex
       Kernel.warn "[Listen warning]: Change block raised an exception: #{$!}"
       Kernel.warn "Backtrace:\n\t#{ex.backtrace.join("\n\t")}"
     end
 
     def _pop_changes
-      changes = { modified: [], added: [], removed: [] }
-      until @changes.empty?
-        change = @changes.pop
-        change.each { |k, v| changes[k] << v.to_s }
-      end
-      changes.each { |_, v| v.uniq! }
+      popped = []
+      popped << @changes.pop until @changes.empty?
+      popped
+    end
+
+    def _smoosh_changes changes
+      smooshed = { modified: [], added: [], removed: [] }
+      changes.each { |h| type = h.keys.first; smooshed[type] << h[type].to_s }
+      smooshed.each { |_, v| v.uniq! }
+      smooshed
     end
   end
 end

spec/acceptance/tcp_spec.rb

@@ -86,7 +86,7 @@
     end
 
     it 'receives changes over TCP' do
-      expect(listen {
+      expect(listen(1) {
         touch 'file.rb'
       }).to eq(
         modified: [],
@@ -98,7 +98,7 @@
     it 'may be paused and unpaused' do
       recipient.pause
 
-      expect(listen {
+      expect(listen(1) {
         touch 'file.rb'
       }).to eq(
         modified: [],
@@ -108,7 +108,7 @@
 
       recipient.unpause
 
-      expect(listen {
+      expect(listen(1) {
         touch 'file.rb'
       }).to eq(
         modified: ['file.rb'],
@@ -120,7 +120,7 @@
     it 'may be stopped and restarted' do
       recipient.stop
 
-      expect(listen {
+      expect(listen(1) {
         touch 'file.rb'
       }).to eq(
         modified: [],
@@ -130,7 +130,7 @@
 
       recipient.start
 
-      expect(listen {
+      expect(listen(1) {
         touch 'file.rb'
       }).to eq(
         modified: ['file.rb'],

spec/lib/listen/listener_spec.rb

@@ -114,7 +114,7 @@
       listener.block = block_stub
       expect(block_stub).to receive(:call).with(['foo'], [], [])
       listener.start
-      sleep 0.01
+      sleep 0.25
     end
   end
 
@@ -268,4 +268,36 @@
     end
   end
 
+  describe '_wait_for_changes' do
+    it 'works' do
+
+      fake_time = 0
+      listener.stub(:sleep) { |sec| fake_time += sec; listener.stopping = true if fake_time > 1 }
+
+      modified = []
+      added = []
+      removed = []
+      listener.block = proc { |m,a,r| modified += m; added += a; removed += r; }
+
+      i = 0
+      listener.stub(:_pop_changes) do
+        i+=1
+        case i
+          when 1
+            [{modified: 'foo.txt'}]
+          when 2
+            [{added: 'bar.txt'}]
+          else
+            []
+        end
+      end
+
+      listener.send :_wait_for_changes
+
+      expect(modified).to eql(['foo.txt'])
+      expect(added).to eql(['bar.txt'])
+
+    end
+  end
+
 end

spec/support/acceptance_helper.rb

@@ -1,9 +1,9 @@
-def listen
-  sleep 0.5 # wait for changes
+def listen lag = 0.5
+  sleep lag # wait for changes
   sleep_until_next_second
   reset_changes
   yield
-  sleep 0.5 # wait for changes
+  sleep lag # wait for changes
   @changes
 end