VCS: short diff to be loaded in background through generic loader

platform/vcs-api/src/com/intellij/openapi/vcs/Details.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2000-2011 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.openapi.vcs;
+
+/**
+ * @author irengrig
+ *         Date: 7/5/11
+ *         Time: 7:32 PM
+ */
+public interface Details<Id, Data> {
+  void take(Id id, Data data);
+  Id getCurrentlySelected();
+}

platform/vcs-api/src/com/intellij/openapi/vcs/GenericDetailsLoader.java

@@ -28,7 +28,7 @@ import java.util.concurrent.atomic.AtomicReference;
  *         Date: 6/29/11
  *         Time: 11:38 PM
  */
-public class GenericDetailsLoader<Id, Data> implements PairConsumer<Id, Data> {
+public class GenericDetailsLoader<Id, Data> implements Details<Id,Data> {
   private final Consumer<Id> myLoader;
   private final ValueConsumer<Id, Data> myValueConsumer;
   private final AtomicReference<Id> myCurrentlySelected;
@@ -39,21 +39,27 @@ public class GenericDetailsLoader<Id, Data> implements PairConsumer<Id, Data> {
     myCurrentlySelected = new AtomicReference<Id>(null);
   }
 
-  public void updateSelection(@Nullable final Id id) {
+  public void updateSelection(@Nullable final Id id, boolean force) {
     ApplicationManager.getApplication().assertIsDispatchThread();
     myValueConsumer.setId(id);
 
-    if (! Comparing.equal(id, myCurrentlySelected.getAndSet(id))) {
+    final Id wasId = myCurrentlySelected.getAndSet(id);
+    if (force || ! Comparing.equal(id, wasId)) {
       myLoader.consume(id);
     }
   }
 
+  public void setCacheConsumer(final PairConsumer<Id, Data>  cacheConsumer) {
+    myValueConsumer.setCacheConsumer(cacheConsumer);
+  }
+
   @Override
-  public void consume(Id id, Data data) {
+  public void take(Id id, Data data) {
     ApplicationManager.getApplication().assertIsDispatchThread();
     myValueConsumer.consume(id, data);
   }
 
+  @Override
   public Id getCurrentlySelected() {
     return myCurrentlySelected.get();
   }

platform/vcs-api/src/com/intellij/openapi/vcs/ValueConsumer.java

@@ -26,14 +26,23 @@ public class ValueConsumer<Id, Data> {
   private Id myId;
   private Id mySetId;
   private final PairConsumer<Id, Data> myConsumer;
+  private PairConsumer<Id, Data> myCacheConsumer;
 
   protected ValueConsumer(PairConsumer<Id, Data> consumer) {
     myConsumer = consumer;
   }
 
+  public void setCacheConsumer(PairConsumer<Id, Data> cacheConsumer) {
+    myCacheConsumer = cacheConsumer;
+  }
+
   public void consume(final Id id, final Data data) {
-    if (id.equals(mySetId)) return; // already set
-    if (! id.equals(myId)) return;
+    if (id.equals(mySetId) || ! id.equals(myId)) {
+      if (myCacheConsumer != null) {
+        myCacheConsumer.consume(id, data);
+      }
+      return;
+    }
     mySetId = id;
     myConsumer.consume(id, data);
   }

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/BinaryDiffRequestFromChange.java

@@ -37,11 +37,13 @@ public class BinaryDiffRequestFromChange implements DiffRequestFromChange<DiffCo
     myProject = project;
   }
 
+  @Override
+  public boolean canCreateRequest(Change change) {
+    return ShowDiffAction.isBinaryChange(myProject, change);
+  }
+
   @Override
   public List<BeforeAfter<DiffContent>> createRequestForChange(Change change, int extraLines) throws VcsException {
-    if (ShowDiffAction.isBinaryChange(myProject, change)) {
-      return Collections.singletonList(ShowDiffAction.createBinaryDiffContents(myProject, change));
-    }
-    return null;
+    return Collections.singletonList(ShowDiffAction.createBinaryDiffContents(myProject, change));
   }
 }

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/ChangesViewManager.java

@@ -54,6 +54,8 @@ import com.intellij.ui.ScrollPaneFactory;
 import com.intellij.ui.content.Content;
 import com.intellij.ui.content.ContentFactory;
 import com.intellij.util.Alarm;
+import com.intellij.util.Consumer;
+import com.intellij.util.PairConsumer;
 import com.intellij.util.PlatformIcons;
 import com.intellij.util.containers.SLRUMap;
 import com.intellij.util.messages.MessageBusConnection;
@@ -98,10 +100,8 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
   @NonNls private static final String ATT_SHOW_IGNORED = "show_ignored";
   private static final Logger LOG = Logger.getInstance("#com.intellij.openapi.vcs.changes.ChangesViewManager");
   private Splitter mySplitter;
-  // todo group somewhere
-  private JPanel myNoDetailsPanel;
-  private JPanel myNothingSelected;
-  private JPanel myNotLoadedYet;
+  private DetailsPanel myDetailsPanel;
+  private GenericDetailsLoader<Change, Pair<JPanel, Disposable>> myDetailsLoader;
   private boolean myDetailsOn;
   private ChangesViewManager.MyFileListener myFileListener;
   private final SLRUMap<FilePath, Pair<JPanel, Disposable>> myDetailsCache;
@@ -111,6 +111,8 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
   private Runnable myUpdateDetails;
   private MessageBusConnection myConnection;
   private ChangesViewManager.ToggleDetailsAction myToggleDetailsAction;
+  private PairConsumer<Change,Pair<JPanel, Disposable>> myDetailsConsumer;
+  private final TreeSelectionListener myTsl;
 
   public static ChangesViewI getInstance(Project project) {
     return PeriodicalTasksCloser.getInstance().safeGetComponent(project, ChangesViewI.class);
@@ -121,9 +123,6 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
     myContentManager = contentManager;
     myVcsChangeDetailsManager = vcsChangeDetailsManager;
     myView = new ChangesListView(project);
-    myNoDetailsPanel = UIVcsUtil.errorPanel("No details available", false);
-    myNothingSelected = UIVcsUtil.errorPanel("Nothing selected", false);
-    myNotLoadedYet = UIVcsUtil.errorPanel("Changes content is not loaded yet", false);
 
     Disposer.register(project, myView);
     myRepaintAlarm = new Alarm(Alarm.ThreadToUse.SWING_THREAD, project);
@@ -144,6 +143,12 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
         changeDetails();
       }
     };
+    myTsl = new TreeSelectionListener() {
+      @Override
+      public void valueChanged(TreeSelectionEvent e) {
+        changeDetails();
+      }
+    };
   }
 
   public void projectOpened() {
@@ -173,6 +178,12 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
   }
 
   public void projectClosed() {
+    if (myToggleDetailsAction.isSelected(null)) {
+      VirtualFileManager.getInstance().removeVirtualFileListener(myFileListener);
+      EditorFactory.getInstance().getEventMulticaster().removeDocumentListener(myDocumentListener);
+    }
+    myDetailsPanel.clear();
+    myView.removeTreeSelectionListener(myTsl);
     myConnection.disconnect();
     myDetailsCache.clear();
     myDisposed = true;
@@ -244,56 +255,92 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
     content.add(myProgressLabel, BorderLayout.SOUTH);
     panel.setContent(content);
 
+    myDetailsPanel = new DetailsPanel();
+    initDetailsLoader();
+
     myView.installDndSupport(ChangeListManagerImpl.getInstanceImpl(myProject));
-    myView.addTreeSelectionListener(new TreeSelectionListener() {
-      @Override
-      public void valueChanged(TreeSelectionEvent e) {
-        changeDetails();
-      }
-    });
+    myView.addTreeSelectionListener(myTsl);
     return panel;
   }
 
+  private void initDetailsLoader() {
+    final PairConsumer<Change, Pair<JPanel, Disposable>> cacheConsumer = new PairConsumer<Change, Pair<JPanel, Disposable>>() {
+      @Override
+      public void consume(Change change, Pair<JPanel, Disposable> pair) {
+        final FilePath filePath = ChangesUtil.getFilePath(change);
+        final Pair<JPanel, Disposable> old = myDetailsCache.get(filePath);
+        if (old == null) {
+          myDetailsCache.put(filePath, pair);
+        } else if (old != pair) {
+          Disposer.dispose(pair.getSecond());
+        }
+      }
+    };
+    myDetailsConsumer = new PairConsumer<Change, Pair<JPanel, Disposable>>() {
+      @Override
+      public void consume(Change change, Pair<JPanel, Disposable> pair) {
+        cacheConsumer.consume(change, pair);
+        myDetailsPanel.data(pair.getFirst());
+        myDetailsPanel.layout();
+      }
+    };
+    myDetailsLoader = new GenericDetailsLoader<Change, Pair<JPanel, Disposable>>(new Consumer<Change>() {
+      @Override
+      public void consume(Change change) {
+        final FilePath filePath = ChangesUtil.getFilePath(change);
+        Pair<JPanel, Disposable> details = myDetailsCache.get(filePath);
+        if (details != null) {
+          myDetailsConsumer.consume(change, details);
+        } else if (myVcsChangeDetailsManager.getPanel(change)) {
+          myDetailsPanel.loading();
+          myDetailsPanel.layout();
+        }
+      }
+    }, myDetailsConsumer);
+    myDetailsLoader.setCacheConsumer(cacheConsumer);
+    myVcsChangeDetailsManager.setDetails(myDetailsLoader);
+  }
+
   private void changeDetails() {
     if (! myDetailsOn) {
-      setChangeDetailsPanel(null);
+      if (mySplitter.getSecondComponent() != null) {
+        setChangeDetailsPanel(null);
+      }
     } else {
-      final Change[] selectedChanges = myView.getSelectedChanges();
-      if (selectedChanges.length == 0) {
-        setChangeDetailsPanel(myNothingSelected);
-      } else {
-        final String freezed = ChangeListManager.getInstance(myProject).isFreezed();
-        if (freezed != null) {
-          setChangeDetailsPanel(UIVcsUtil.errorPanel(freezed, false));
+      setDetails();
+      myDetailsPanel.layout();
+
+      if (mySplitter.getSecondComponent() == null) {
+        setChangeDetailsPanel(myDetailsPanel.myPanel);
+      }
+    }
+  }
+
+  private void setDetails() {
+    final Change[] selectedChanges = myView.getSelectedChanges();
+    if (selectedChanges.length == 0) {
+      myDetailsPanel.nothingSelected();
+    } else {
+      final String freezed = ChangeListManager.getInstance(myProject).isFreezed();
+      if (freezed != null) {
+        myDetailsPanel.data(UIVcsUtil.errorPanel(freezed, false));
+        return;
+      }
+
+      myDetailsPanel.notAvailable();
+      for (Change change : selectedChanges) {
+        if (change.getBeforeRevision() instanceof FakeRevision || change.getAfterRevision() instanceof FakeRevision) {
+          myDetailsPanel.loadingInitial();
           return;
         }
-        Pair<JPanel, Disposable> details = null;
-        FilePath filePath = null;
-        for (Change change : selectedChanges) {
-          if (change.getBeforeRevision() instanceof FakeRevision || change.getAfterRevision() instanceof FakeRevision) {
-            setChangeDetailsPanel(myNotLoadedYet);
-            return;
-          }
-          filePath = ChangesUtil.getFilePath(change);
-          details = myDetailsCache.get(filePath);
-          if (details != null) break;
-          details = myVcsChangeDetailsManager.getPanel(change);
-          if (details != null) {
-            myDetailsCache.put(filePath, details);
-            break;
-          }
+        if (myVcsChangeDetailsManager.canComment(change)) {
+          myDetailsFilePath = ChangesUtil.getFilePath(change);
+          myDetailsLoader.updateSelection(change, true);
+          return;
         }
-
-        final JPanel panel;
-        if (details == null) {
-          panel = myNoDetailsPanel;
-        }
-        else {
-          myDetailsFilePath = filePath;
-          panel = details.getFirst();
-        }
-        setChangeDetailsPanel(panel);
       }
+
+      myDetailsPanel.notAvailable();
     }
   }
 
@@ -580,4 +627,61 @@ public class ChangesViewManager implements ChangesViewI, JDOMExternalizable, Pro
       }
     }
   }
+
+  private static class DetailsPanel {
+    private CardLayout myLayout;
+    private JPanel myPanel;
+    private JPanel myDataPanel;
+    private Layer myCurrentLayer;
+
+    private DetailsPanel() {
+      myPanel = new JPanel();
+      myLayout = new CardLayout();
+      myPanel.setLayout(myLayout);
+      myDataPanel = new JPanel(new BorderLayout());
+
+      myPanel.add(UIVcsUtil.errorPanel("No details available", false), Layer.notAvailable.name());
+      myPanel.add(UIVcsUtil.errorPanel("Nothing selected", false), Layer.nothingSelected.name());
+      myPanel.add(UIVcsUtil.errorPanel("Changes content is not loaded yet", false), Layer.notLoadedInitial.name());
+      myPanel.add(UIVcsUtil.errorPanel("Loading...", false), Layer.loading.name());
+      myPanel.add(myDataPanel, Layer.data.name());
+    }
+
+    public void nothingSelected() {
+      myCurrentLayer = Layer.nothingSelected;
+    }
+
+    public void notAvailable() {
+      myCurrentLayer = Layer.notAvailable;
+    }
+
+    public void loading() {
+      myCurrentLayer = Layer.loading;
+    }
+
+    public void loadingInitial() {
+      myCurrentLayer = Layer.notLoadedInitial;
+    }
+
+    public void data(final JPanel panel) {
+      myCurrentLayer = Layer.data;
+      myPanel.add(panel, Layer.data.name());
+    }
+
+    public void layout() {
+      myLayout.show(myPanel, myCurrentLayer.name());
+    }
+
+    public void clear() {
+      myPanel.removeAll();
+    }
+
+    private static enum Layer {
+      notAvailable,
+      nothingSelected,
+      notLoadedInitial,
+      loading,
+      data,
+    }
+  }
 }

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/FragmentedDiffRequestFromChange.java

@@ -64,11 +64,17 @@ public class FragmentedDiffRequestFromChange implements DiffRequestFromChange<Sh
   }
 
   @Override
+  public boolean canCreateRequest(Change change) {
+    if (ChangesUtil.isTextConflictingChange(change)) return false;
+    if (ShowDiffAction.isBinaryChange(myProject, change)) return false;
+    final FilePath filePath = ChangesUtil.getFilePath(change);
+    if (filePath.isDirectory()) return false;
+    return true;
+  }
+
+  @Override
   public List<BeforeAfter<ShiftedSimpleContent>> createRequestForChange(Change change, int extraLines) throws VcsException {
-    if (ChangesUtil.isTextConflictingChange(change)) return null;
-    if (ShowDiffAction.isBinaryChange(myProject, change)) return null;
     final FilePath filePath = ChangesUtil.getFilePath(change);
-    if (filePath.isDirectory()) return null;
 
     final RangesCalculator calculator = new RangesCalculator();
     calculator.execute(change, filePath, myRangesCache, LineStatusTrackerManager.getInstance(myProject));
@@ -216,7 +222,7 @@ public class FragmentedDiffRequestFromChange implements DiffRequestFromChange<Sh
       final Document oldDocument = new DocumentImpl(true);
       // todo !!! a question how to show line separators in diff etc
       // todo currently document doesn't allow to put \r as separator
-      oldDocument.setText(StringUtil.convertLineSeparators(notNullContentRevision(cr)));
+      oldDocument.replaceString(0, oldDocument.getTextLength(), StringUtil.convertLineSeparators(notNullContentRevision(cr)));
       oldDocument.setReadOnly(true);
       return oldDocument;
     }

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/TransparentlyFailedValue.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2000-2011 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.openapi.vcs.changes;
+
+/**
+ * @author irengrig
+ *         Date: 7/5/11
+ *         Time: 3:35 PM
+ */
+public class TransparentlyFailedValue<T, E extends Exception> {
+  private T t;
+  private E e;
+
+  public void set(final T t) {
+    this.t = t;
+  }
+
+  public void fail(final E e) {
+    this.e = e;
+  }
+
+  public T get() throws E {
+    if (this.e != null) throw this.e;
+    return this.t;
+  }
+}

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/VcsChangeDetailsManager.java

@@ -21,17 +21,22 @@ import com.intellij.openapi.diff.DiffContent;
 import com.intellij.openapi.diff.DiffPanel;
 import com.intellij.openapi.diff.ShiftedSimpleContent;
 import com.intellij.openapi.diff.impl.DiffPanelImpl;
+import com.intellij.openapi.progress.BackgroundTaskQueue;
+import com.intellij.openapi.progress.ProgressIndicator;
+import com.intellij.openapi.progress.Task;
 import com.intellij.openapi.project.Project;
+import com.intellij.openapi.util.Comparing;
 import com.intellij.openapi.util.Disposer;
 import com.intellij.openapi.util.Pair;
+import com.intellij.openapi.vcs.Details;
 import com.intellij.openapi.vcs.VcsException;
 import com.intellij.openapi.vcs.VcsKey;
 import com.intellij.openapi.vcs.changes.actions.DiffRequestFromChange;
 import com.intellij.ui.components.JBScrollPane;
 import com.intellij.util.BeforeAfter;
-import com.intellij.util.containers.Convertor;
 import com.intellij.util.containers.HashMap;
 import com.intellij.vcsUtil.UIVcsUtil;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
 import javax.swing.*;
@@ -49,15 +54,18 @@ import java.util.Map;
  */
 public class VcsChangeDetailsManager {
   private static final int extraLines = 2;
-  private final Map<VcsKey, Convertor<Change, Pair<JPanel, Disposable>>> myProviderMap = new HashMap<VcsKey, Convertor<Change, Pair<JPanel, Disposable>>>();
-  private final List<Convertor<Change, Pair<JPanel, Disposable>>> myDedicatedList;
+  private final Map<VcsKey, VcsChangeDetailsProvider> myProviderMap = new HashMap<VcsKey, VcsChangeDetailsProvider>();
+  private final List<VcsChangeDetailsProvider> myDedicatedList;
   // todo also check for size
   private final LinkedList<DiffPanel> myDiffPanelCache;
   private final Project myProject;
+  private Details<Change, Pair<JPanel, Disposable>> myDetails;
+  private final BackgroundTaskQueue myQueue;
 
   public VcsChangeDetailsManager(final Project project) {
     myProject = project;
-    myDedicatedList = new ArrayList<Convertor<Change,Pair<JPanel, Disposable>>>();
+    myQueue = new BackgroundTaskQueue(myProject, "Loading change details");
+    myDedicatedList = new ArrayList<VcsChangeDetailsProvider>();
 
     myDiffPanelCache = new LinkedList<DiffPanel>();
     myDedicatedList.add(new BinaryDiffDetailsProvider(project, myDiffPanelCache));
@@ -66,6 +74,7 @@ public class VcsChangeDetailsManager {
     Disposer.register(project, new Disposable() {
       @Override
       public void dispose() {
+        myQueue.clear();
         for (DiffPanel diffPanel : myDiffPanelCache) {
           Disposer.dispose(diffPanel);
         }
@@ -73,19 +82,67 @@ public class VcsChangeDetailsManager {
     });
   }
 
+  public void setDetails(Details<Change, Pair<JPanel, Disposable>> details) {
+    myDetails = details;
+  }
+
+  public boolean canComment(final Change change) {
+    return getProvider(change) != null;
+  }
+
   @Nullable
-  public Pair<JPanel, Disposable> getPanel(final Change change) {
-    // text details
-    for (Convertor<Change, Pair<JPanel, Disposable>> convertor : myDedicatedList) {
-      final Pair<JPanel, Disposable> pair = convertor.convert(change);
-      if (pair != null) {
-        return pair;
-      }
+  private VcsChangeDetailsProvider getProvider(final Change change) {
+    for (VcsChangeDetailsProvider provider : myDedicatedList) {
+      if (provider.canComment(change)) return provider;
     }
     return null;
   }
 
-  private static class BinaryDiffDetailsProvider implements Convertor<Change,Pair<JPanel, Disposable>> {
+  // true -> loading
+  public boolean getPanel(final Change change) {
+    // text details
+    final VcsChangeDetailsProvider<?> provider = getProvider(change);
+    if (provider == null) {
+      return false;
+    }
+
+    myQueue.run(new LoaderTask(myProject, provider, change, myDetails));
+    return true;
+  }
+
+  private static class LoaderTask<T> extends Task.Backgroundable {
+    private T myResult;
+    private final VcsChangeDetailsProvider<T> myProvider;
+    private final Change myChange;
+    private final Details<Change, Pair<JPanel, Disposable>> myDetails;
+
+    private LoaderTask(@Nullable Project project, final VcsChangeDetailsProvider provider, final Change change,
+                       final Details<Change, Pair<JPanel, Disposable>> consumer) {
+      super(project, provider.getProgressTitle(), false, BackgroundFromStartOption.getInstance());
+      myProvider = provider;
+      myChange = change;
+      myDetails = consumer;
+    }
+
+    @Override
+    public void run(@NotNull ProgressIndicator indicator) {
+      if (myProject.isDisposed() || ! myProject.isOpen() || !Comparing.equal(myChange, myDetails.getCurrentlySelected())) return;
+      //if (! myProvider.canComment(myChange)) return;
+      myResult = myProvider.load(myChange);
+    }
+
+    @Override
+    public void onSuccess() {
+      if (myProject.isDisposed() || ! myProject.isOpen()) return;
+      if (myResult != null) {
+        final Pair<JPanel, Disposable> pair = myProvider.comment(myChange, myResult);
+        myDetails.take(myChange, pair);
+      }
+      // todo else?
+    }
+  }
+
+  private static class BinaryDiffDetailsProvider implements VcsChangeDetailsProvider<ValueWithVcsException<List<BeforeAfter<DiffContent>>>> {
     private final BinaryDiffRequestFromChange myRequestFromChange;
     private final Project myProject;
     private DiffPanelHolder myDiffPanelHolder;
@@ -97,15 +154,26 @@ public class VcsChangeDetailsManager {
     }
 
     @Override
-    public Pair<JPanel, Disposable> convert(Change o) {
+    public String getProgressTitle() {
+      return "Loading change content";
+    }
+
+    @Override
+    public boolean canComment(Change change) {
+      return myRequestFromChange.canCreateRequest(change);
+    }
+
+    @Override
+    public Pair<JPanel, Disposable> comment(Change change, ValueWithVcsException<List<BeforeAfter<DiffContent>>> value) {
       final List<BeforeAfter<DiffContent>> contents;
       try {
-        contents = myRequestFromChange.createRequestForChange(o, 0);
+        contents = value.get();
+        if (contents == null) throw new VcsException("Can not load content");
       }
       catch (VcsException e) {
         return new Pair<JPanel, Disposable>(UIVcsUtil.errorPanel(e.getMessage(), true), null);
       }
-      if (contents == null || contents.isEmpty()) return null;
+      if (contents.isEmpty()) return noDifferences();
       assert contents.size() == 1;
       final DiffPanel panel = myDiffPanelHolder.getOrCreate();
       panel.setContents(contents.get(0).getBefore(), contents.get(0).getAfter());
@@ -116,7 +184,7 @@ public class VcsChangeDetailsManager {
       final JPanel wrapper = new JPanel();
       final BoxLayout boxLayout = new BoxLayout(wrapper, BoxLayout.X_AXIS);
       wrapper.setLayout(boxLayout);
-      final JLabel label = new JLabel(changeDescription(o));
+      final JLabel label = new JLabel(changeDescription(change));
       label.setBorder(BorderFactory.createEmptyBorder(1,2,0,0));
       wrapper.add(label);
       topPanel.add(wrapper, BorderLayout.CENTER);
@@ -131,9 +199,37 @@ public class VcsChangeDetailsManager {
         }
       });
     }
+
+    @Override
+    public ValueWithVcsException<List<BeforeAfter<DiffContent>>> load(final Change change) {
+      return new ValueWithVcsException<List<BeforeAfter<DiffContent>>>() {
+        @Override
+        protected List<BeforeAfter<DiffContent>> computeImpl() throws VcsException {
+          return myRequestFromChange.createRequestForChange(change, 0);
+        }
+      };
+    }
   }
 
-  private static class FragmentedDiffDetailsProvider implements Convertor<Change,Pair<JPanel, Disposable>> {
+  private abstract static class ValueWithVcsException<T> extends TransparentlyFailedValue<T, VcsException> {
+    protected ValueWithVcsException() {
+      try {
+        set(computeImpl());
+      }
+      catch (VcsException e) {
+        fail(e);
+      }
+    }
+
+    protected abstract T computeImpl() throws VcsException;
+  }
+
+  private static Pair<JPanel, Disposable> noDifferences() {
+    return new Pair<JPanel, Disposable>(
+      UIVcsUtil.errorPanel(DiffBundle.message("diff.contents.have.differences.only.in.line.separators.message.text"), false), null);
+  }
+
+  private static class FragmentedDiffDetailsProvider implements VcsChangeDetailsProvider<ValueWithVcsException<List<BeforeAfter<ShiftedSimpleContent>>>> {
     private final DiffRequestFromChange<ShiftedSimpleContent> myRequestFromChange;
     private final Project myProject;
     private final LinkedList<DiffPanel> myDiffPanelCache;
@@ -147,14 +243,33 @@ public class VcsChangeDetailsManager {
     }
 
     @Override
-    public Pair<JPanel, Disposable> convert(Change o) {
+    public String getProgressTitle() {
+      return "Loading change content";
+    }
+
+    @Override
+    public boolean canComment(Change change) {
+      return myRequestFromChange.canCreateRequest(change);
+    }
+
+    @Override
+    public ValueWithVcsException<List<BeforeAfter<ShiftedSimpleContent>>> load(final Change change) {
+      return new ValueWithVcsException<List<BeforeAfter<ShiftedSimpleContent>>>() {
+        @Override
+        protected List<BeforeAfter<ShiftedSimpleContent>> computeImpl() throws VcsException {
+          return myRequestFromChange.createRequestForChange(change, extraLines);
+        }
+      };
+    }
+
+    @Override
+    public Pair<JPanel, Disposable> comment(Change change, ValueWithVcsException<List<BeforeAfter<ShiftedSimpleContent>>> value) {
       final List<BeforeAfter<ShiftedSimpleContent>> requestForChange;
       try {
-        requestForChange = myRequestFromChange.createRequestForChange(o, extraLines);
-        if (requestForChange == null) return null;
+        requestForChange = value.get();
+        if (requestForChange == null) throw new VcsException("Can not load content");
         if (requestForChange.isEmpty()) {
-          return new Pair<JPanel, Disposable>(
-            UIVcsUtil.errorPanel(DiffBundle.message("diff.contents.have.differences.only.in.line.separators.message.text"), false), null);
+          return noDifferences();
         }
       }
       catch (VcsException e) {
@@ -162,11 +277,10 @@ public class VcsChangeDetailsManager {
       }
 
       final ChangesFragmentedDiffPanel panel =
-        new ChangesFragmentedDiffPanel(myProject, requestForChange, myDiffPanelCache, changeDescription(o));
+        new ChangesFragmentedDiffPanel(myProject, requestForChange, myDiffPanelCache, changeDescription(change));
       panel.buildUi();
       return new Pair<JPanel, Disposable>(panel.getPanel(), panel);
     }
-
   }
 
   private static String changeDescription(Change o) {

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/VcsChangeDetailsProvider.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2000-2011 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.intellij.openapi.vcs.changes;
+
+import com.intellij.openapi.Disposable;
+import com.intellij.openapi.util.Pair;
+import com.intellij.openapi.vcs.CalledInAwt;
+import com.intellij.openapi.vcs.CalledInBackground;
+
+import javax.swing.*;
+
+/**
+ * @author irengrig
+ *         Date: 7/5/11
+ *         Time: 2:49 PM
+ */
+public interface VcsChangeDetailsProvider<T> {
+  String getProgressTitle();
+  @CalledInAwt
+  boolean canComment(final Change change);
+  @CalledInBackground
+  T load(final Change change);
+  @CalledInAwt
+  Pair<JPanel, Disposable> comment(final Change change, final T t);
+}

platform/vcs-impl/src/com/intellij/openapi/vcs/changes/actions/DiffRequestFromChange.java

@@ -29,6 +29,7 @@ import java.util.List;
  *         Time: 6:39 PM
  */
 public interface DiffRequestFromChange<T extends DiffContent> {
+  boolean canCreateRequest(final Change change);
   @Nullable
   List<BeforeAfter<T>> createRequestForChange(final Change change, int extraLines) throws VcsException;
 }

plugins/git4idea/src/git4idea/history/wholeTree/GitLogUI.java

@@ -312,7 +312,7 @@ public class GitLogUI implements Disposable {
           question.putValue(commitI.selectRepository(myRootsUnderVcs), commitI.getHash());
           myDetailsCache.acceptQuestion(question);
         } else {
-          myDetailsLoader.consume(commitI, gitCommit);
+          myDetailsLoader.take(commitI, gitCommit);
         }
       }
     };
@@ -342,7 +342,7 @@ public class GitLogUI implements Disposable {
         final VirtualFile root = commitI.selectRepository(myRootsUnderVcs);
         final List<String> branches = myDetailsCache.getBranches(root, commitI.getHash());
         if (branches != null) {
-          myBranchesLoader.consume(commitI, branches);
+          myBranchesLoader.take(commitI, branches);
           return;
         }
 
@@ -350,7 +350,7 @@ public class GitLogUI implements Disposable {
           @Override
           public void consume(List<String> strings) {
             if (myProject.isDisposed() || strings == null) return;
-            myBranchesLoader.consume(commitI, strings);
+            myBranchesLoader.take(commitI, strings);
           }
         }, myRecheck);
       }
@@ -447,19 +447,19 @@ public class GitLogUI implements Disposable {
 
     if (meaningfulRows == 0) {
       myDetailsPanel.nothingSelected();
-      myDetailsLoader.updateSelection(null);
-      myBranchesLoader.updateSelection(null);
+      myDetailsLoader.updateSelection(null, false);
+      myBranchesLoader.updateSelection(null, false);
     } else if (meaningfulRows == 1) {
       final GitCommit commit = fullCommitPresentation(commitAt);
       if (commit == null) {
         myDetailsPanel.loading(commitAt.selectRepository(myRootsUnderVcs));
       }
-      myDetailsLoader.updateSelection(commitAt);
-      myBranchesLoader.updateSelection(commitAt);
+      myDetailsLoader.updateSelection(commitAt, false);
+      myBranchesLoader.updateSelection(commitAt, false);
     } else {
       myDetailsPanel.severalSelected();
-      myDetailsLoader.updateSelection(null);
-      myBranchesLoader.updateSelection(null);
+      myDetailsLoader.updateSelection(null, false);
+      myBranchesLoader.updateSelection(null, false);
     }
   }