src/share/classes/com/sun/tools/sjavac/BuildState.java

*** 24,35 ****
--- 24,38 ----
   */
  
  package com.sun.tools.sjavac;
  
  import java.io.File;
+ import java.util.ArrayList;
+ import java.util.Collections;
  import java.util.HashMap;
  import java.util.HashSet;
+ import java.util.List;
  import java.util.Map;
  import java.util.Set;
  
  /**
   * The build state class captures the source code and generated artifacts
*** 46,61 ****
--- 49,68 ----
      private Map<String,Package> packages = new HashMap<>();
      private Map<String,Source> sources = new HashMap<>();
      private Map<String,File> artifacts = new HashMap<>();
      // Map from package to a set of packages that depend on said package.
      private Map<String,Set<String>> dependents = new HashMap<>();
+     // All Archives that are found to have the same timestamps as in the javac_state file are stored here.
+     // If a archive is not found here, it is either new, or its timestamps has changed.
+     private Set<String> archives = new HashSet<>();
  
      public  Map<String,Module> modules() { return modules; }
      public  Map<String,Package> packages() { return packages; }
      public  Map<String,Source> sources() { return sources; }
      public  Map<String,File> artifacts() { return artifacts; }
      public  Map<String,Set<String>> dependents() { return dependents; }
+     public  Set<String> archives() { return archives; }
  
      /**
       * Lookup a module from a name. Create the module if it does
       * not exist yet.
       */
*** 260,269 ****
--- 267,306 ----
          sources.put(s.name(), s);
          return s;
      }
  
      /**
+      * Add to archives, but only if the timestamp is the same, ie the archive is 
+      * probably unchanged.
+      */
+     public void loadArchiveTimestamp(String l) {
+         int p = l.indexOf(' ', 2);
+         String archive = l.substring(2, p);
+         long timestamp = Long.parseLong(l.substring(p+1));
+         File f = new File(archive);
+         if (f.lastModified() == timestamp) {
+             Log.trace("Same timestamp for "+archive);
+             archives.add(archive);
+         } else {
+             Log.debug("Timestamp changed for "+archive);
+         }
+     }
+ 
+     /**
+      * Save archive with timestamp info.
+      */
+     public void saveArchiveTimestamps(StringBuilder b) {
+         List<String> sorted = new ArrayList<>();
+         sorted.addAll(archives);
+         Collections.sort(sorted);
+         for (String a : sorted) {
+             File f = new File(a);
+             b.append("Z "+a+" "+f.lastModified()+"\n");
+         }
+     }
+ 
+     /**
       * During an incremental compile we need to copy the old javac state
       * information about packages that were not recompiled.
       */
      public void copyPackagesExcept(BuildState prev, Set<String> recompiled, Set<String> removed) {
          for (String pkg : prev.packages().keySet()) {