Aggressively cache Screen widgets to accelerate forward/back

When browsing changes it is very common for a user to be on their own
dashboard, click on a change, jump back, then jump to another change.
We want to make the "jump back" part really fast.  Its unlikely that
the data in the dashboard has really changed since the last time the
user looked at it, so recycling the entire widget graph saves us time
in constructing the DOM elements over again for the table.  If rows
did get removed or were inserted the table will update itself once the
RPC call is complete.

Signed-off-by: Shawn O. Pearce <sop@google.com>

webapp/src/com/google/gerrit/client/changes/AccountDashboardScreen.java

@@ -14,12 +14,12 @@
 
 package com.google.gerrit.client.changes;
 
+import com.google.gerrit.client.Link;
 import com.google.gerrit.client.data.AccountDashboardInfo;
 import com.google.gerrit.client.data.AccountInfo;
 import com.google.gerrit.client.reviewdb.Account;
 import com.google.gerrit.client.rpc.GerritCallback;
 import com.google.gerrit.client.ui.Screen;
-import com.google.gwt.user.client.History;
 
 
 public class AccountDashboardScreen extends Screen {
@@ -29,44 +29,49 @@ public class AccountDashboardScreen extends Screen {
   private ChangeTable.Section forReview;
   private ChangeTable.Section closed;
 
-  public AccountDashboardScreen() {
-    this(null);
+  public AccountDashboardScreen(final Account.Id id) {
+    ownerId = id;
   }
 
-  public AccountDashboardScreen(final Account.Id id) {
-    super("");
+  @Override
+  public Object getScreenCacheToken() {
+    return getClass();
+  }
 
-    ownerId = id;
-    table = new ChangeTable();
-    byOwner = new ChangeTable.Section("");
-    forReview = new ChangeTable.Section("");
-    closed = new ChangeTable.Section("");
-
-    table.addSection(byOwner);
-    table.addSection(forReview);
-    table.addSection(closed);
-    add(table);
-
-    if (ownerId == null) {
-      setRequiresSignIn(true);
-    }
+  @Override
+  public Screen recycleThis(final Screen newScreen) {
+    ownerId = ((AccountDashboardScreen) newScreen).ownerId;
+    return this;
   }
 
   @Override
   public void onLoad() {
+    if (table == null) {
+      table = new ChangeTable();
+      byOwner = new ChangeTable.Section("");
+      forReview = new ChangeTable.Section("");
+      closed = new ChangeTable.Section("");
+
+      table.addSection(byOwner);
+      table.addSection(forReview);
+      table.addSection(closed);
+      add(table);
+    }
+    table.setSavePointerId(Link.toAccountDashboard(ownerId));
     super.onLoad();
-    table.setSavePointerId(History.getToken());
     Util.LIST_SVC.forAccount(ownerId,
         new GerritCallback<AccountDashboardInfo>() {
           public void onSuccess(final AccountDashboardInfo r) {
-            display(r);
+            // TODO Actually we want to cancel the RPC if detached.
+            if (isAttached()) {
+              display(r);
+            }
           }
         });
   }
 
   private void display(final AccountDashboardInfo r) {
     final AccountInfo o = r.getOwner();
-
     setTitleText(Util.M.accountDashboardTitle(o.getFullName()));
     byOwner.setTitleText(Util.M.changesUploadedBy(o.getFullName()));
     forReview.setTitleText(Util.M.changesReviewableBy(o.getFullName()));

webapp/src/com/google/gerrit/client/changes/ChangeScreen.java

@@ -15,15 +15,34 @@
 package com.google.gerrit.client.changes;
 
 import com.google.gerrit.client.data.ChangeInfo;
+import com.google.gerrit.client.reviewdb.Change;
 import com.google.gerrit.client.ui.Screen;
 
 
 public class ChangeScreen extends Screen {
-  public ChangeScreen(final int id) {
-    super("Loading Change " + id);
+  private Change.Id changeId;
+
+  public ChangeScreen(final Change.Id toShow) {
+    changeId = toShow;
   }
 
   public ChangeScreen(final ChangeInfo c) {
-    super(c.getSubject());
+    this(c.getId());
+  }
+
+  @Override
+  public Object getScreenCacheToken() {
+    return getClass();
+  }
+
+  @Override
+  public Screen recycleThis(final Screen newScreen) {
+    changeId = ((ChangeScreen) newScreen).changeId;
+    return this;
+  }
+
+  @Override
+  public void onLoad() {
+    setTitleText("Change " + changeId.get());
   }
 }

webapp/src/com/google/gerrit/client/changes/ChangeTable.java

@@ -19,7 +19,6 @@ import com.google.gerrit.client.Link;
 import com.google.gerrit.client.SignedInListener;
 import com.google.gerrit.client.data.ChangeInfo;
 import com.google.gerrit.client.reviewdb.Change;
-import com.google.gerrit.client.reviewdb.Change.Id;
 import com.google.gerrit.client.rpc.GerritCallback;
 import com.google.gwt.user.client.Command;
 import com.google.gwt.user.client.DOM;
@@ -73,7 +72,7 @@ public class ChangeTable extends Composite implements HasFocus {
   private static final LinkedHashMap<String, Change.Id> savedPositions =
       new LinkedHashMap<String, Change.Id>(10, 0.75f, true) {
         @Override
-        protected boolean removeEldestEntry(Entry<String, Id> eldest) {
+        protected boolean removeEldestEntry(Entry<String, Change.Id> eldest) {
           return size() >= 5;
         }
       };

webapp/src/com/google/gerrit/client/changes/MineStarredScreen.java

@@ -14,10 +14,10 @@
 
 package com.google.gerrit.client.changes;
 
+import com.google.gerrit.client.Link;
 import com.google.gerrit.client.data.ChangeInfo;
 import com.google.gerrit.client.rpc.GerritCallback;
 import com.google.gerrit.client.ui.AccountScreen;
-import com.google.gwt.user.client.History;
 
 import java.util.List;
 
@@ -33,13 +33,19 @@ public class MineStarredScreen extends AccountScreen {
     starred = new ChangeTable.Section();
 
     table.addSection(starred);
+    table.setSavePointerId(Link.MINE_STARRED);
+
     add(table);
   }
 
+  @Override
+  public Object getScreenCacheToken() {
+    return Link.MINE_STARRED;
+  }
+
   @Override
   public void onLoad() {
     super.onLoad();
-    table.setSavePointerId(History.getToken());
     Util.LIST_SVC.myStarredChanges(new GerritCallback<List<ChangeInfo>>() {
       public void onSuccess(final List<ChangeInfo> result) {
         starred.display(result);