[JENKINS-8929] follow up changes

- AbstractProject.getBuildingUpstream/getBuildingDownstream()
  should be symmetric.
- It's unlikely for us to add another category of items,
  so reverted getUnblockedItems() implementation to the older one
  that was more efficient.
- ItemList was meant to be internal, so keep it as such,
  at least for now.

core/src/main/java/hudson/model/AbstractProject.java

@@ -43,7 +43,6 @@ import hudson.model.Cause.UserCause;
 import hudson.model.Descriptor.FormException;
 import hudson.model.Fingerprint.RangeSet;
 import hudson.model.Queue.Executable;
-import hudson.model.Queue.ItemList;
 import hudson.model.Queue.Task;
 import hudson.model.queue.SubTask;
 import hudson.model.Queue.WaitingItem;
@@ -1082,12 +1081,10 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
      * the given project (provided that all builds went smoothly.)
      */
     protected AbstractProject getBuildingDownstream() {
-    	DependencyGraph graph = Hudson.getInstance().getDependencyGraph();
-        Set<AbstractProject> tups = graph.getTransitiveDownstream(this);
-        Queue queue = Hudson.getInstance().getQueue();
-        ItemList<Queue.Item> unblockedItems = queue.getUnblockedItems();
-        for (AbstractProject tup : tups) {
-			if(tup.isBuilding() || unblockedItems.containsKey(tup))
+        Set<Task> unblockedTasks = Hudson.getInstance().getQueue().getUnblockedTasks();
+
+        for (AbstractProject tup : Hudson.getInstance().getDependencyGraph().getTransitiveDownstream(this)) {
+			if (tup!=this && (tup.isBuilding() || unblockedTasks.contains(tup)))
                 return tup;
         }
         return null;
@@ -1101,10 +1098,10 @@ public abstract class AbstractProject<P extends AbstractProject<P,R>,R extends A
      * the given project (provided that all builds went smoothly.)
      */
     protected AbstractProject getBuildingUpstream() {
-    	DependencyGraph graph = Hudson.getInstance().getDependencyGraph();
-        Set<AbstractProject> tups = graph.getTransitiveUpstream(this);
-        for (AbstractProject tup : tups) {
-            if(tup.isBuilding() || tup.isInQueue())
+        Set<Task> unblockedTasks = Hudson.getInstance().getQueue().getUnblockedTasks();
+
+        for (AbstractProject tup : Hudson.getInstance().getDependencyGraph().getTransitiveUpstream(this)) {
+			if (tup!=this && (tup.isBuilding() || unblockedTasks.contains(tup)))
                 return tup;
         }
         return null;

core/src/main/java/hudson/model/Queue.java

@@ -76,6 +76,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.GregorianCalendar;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Iterator;
 import java.util.LinkedList;
 import java.util.List;
@@ -636,14 +637,31 @@ public class Queue extends ResourceController implements Saveable {
 
     /**
      * Gets all items that are in the queue but not blocked
+     *
+     * @since 1.402
      */
-    synchronized ItemList<Item> getUnblockedItems() {
-    	ItemList<Item> queuedNotBlocked = new ItemList<Item>();
-        queuedNotBlocked.addAll(Arrays.asList(getItems()));
-        queuedNotBlocked.removeAll(blockedProjects);
+    public synchronized List<Item> getUnblockedItems() {
+    	List<Item> queuedNotBlocked = new ArrayList<Item>();
+        queuedNotBlocked.addAll(waitingList);
+        queuedNotBlocked.addAll(buildables);
+        queuedNotBlocked.addAll(pendings);
+        // but not 'blockedProjects'
         return queuedNotBlocked;
     }
 
+    /**
+     * Works just like {@link #getUnblockedItems()} but return tasks.
+     *
+     * @since 1.402
+     */
+    public synchronized Set<Task> getUnblockedTasks() {
+        List<Item> items = getUnblockedItems();
+        Set<Task> unblockedTasks = new HashSet<Task>(items.size());
+        for (Queue.Item t : items)
+            unblockedTasks.add(t.task);
+        return unblockedTasks;
+    }
+
     /**
      * Is the given task currently pending execution?
      */
@@ -1568,7 +1586,7 @@ public class Queue extends ResourceController implements Saveable {
     /**
      * {@link ArrayList} of {@link Item} with more convenience methods.
      */
-    static class ItemList<T extends Item> extends ArrayList<T> {
+    private static class ItemList<T extends Item> extends ArrayList<T> {
     	public T get(Task task) {
     		for (T item: this) {
     			if (item.task == task) {