Switched ChangeDetector to use the last modified times from processing (when the file was last saved or loaded) and compare with the system's last modified time. Added supporting code in SketchCode to get these times. Added a tiny fix in Sketch to allow processing to actually start

app/src/processing/app/ChangeDetector.java

@@ -14,7 +14,8 @@ public class ChangeDetector implements WindowFocusListener {
   private Editor editor;
 
 //  private boolean enabled = true;
-  private boolean enabled = false; // broken on OS X
+  //REMOVE on for testing
+  private boolean enabled = true; // broken on OS X
 
   private boolean skip = false;
 
@@ -39,9 +40,6 @@ public class ChangeDetector implements WindowFocusListener {
   }
 
   private void checkFileChangeAsync() {
-    if(1==1){
-      return;
-    }
     Thread th = new Thread(new Runnable() {
       @Override
       public void run() {
@@ -159,7 +157,7 @@ public class ChangeDetector implements WindowFocusListener {
         reloadSketch(sc);
         return;
       }
-      //if a file's tab was visited after the file was 
+      //if a file's tab was saved before the file was 
       if (sketchFile.lastModified() > sc.lastModified()) {
         reloadSketch(sc);
         return;

app/src/processing/app/Sketch.java

@@ -1210,12 +1210,13 @@ public class Sketch {
     current = code[which];
     currentIndex = which;
     current.visited = System.currentTimeMillis();
+    //REMOVE 
     try {
       editor.setCode(current);
 //    editor.header.rebuild();
       editor.header.repaint();
     } catch (NullPointerException e) {
-      e.printStackTrace();
+      //e.printStackTrace();
     }
   }
 

app/src/processing/app/SketchCode.java

@@ -296,6 +296,7 @@ public class SketchCode {
       System.err.println();
     }
 
+    lastModified = file.lastModified();
     setModified(false);
   }