CPP-8459: don't calculate usage text in EDT

Review: IDEA-CR-32232

platform/usageView/src/com/intellij/usages/UsageInfo2UsageAdapter.java

@@ -432,6 +432,22 @@ public class UsageInfo2UsageAdapter implements UsageInModule,
   @Override
   @NotNull
   public TextChunk[] getText() {
+    return doUpdateCachedText();
+  }
+
+  @Nullable
+  @Override
+  public TextChunk[] getCachedText() {
+    return SoftReference.dereference(myTextChunks);
+  }
+
+  @Override
+  public void updateCachedText() {
+    doUpdateCachedText();
+  }
+
+  @NotNull
+  private TextChunk[] doUpdateCachedText() {
     TextChunk[] chunks = SoftReference.dereference(myTextChunks);
     final long currentModificationStamp = getCurrentModificationStamp();
     boolean isModified = currentModificationStamp != myModificationStamp;

platform/usageView/src/com/intellij/usages/UsagePresentation.java

@@ -16,6 +16,7 @@
 package com.intellij.usages;
 
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import javax.swing.*;
 
@@ -26,6 +27,20 @@ public interface UsagePresentation {
   @NotNull
   TextChunk[] getText();
 
+  /**
+   * If the implementation caches or lazy-loades the text chunks internally, this method gives it a chance to avoid
+   * re-calculating it synchronously on EDT and return the possibly obsolete data.
+   *
+   * The component using this presentation might call {@link UsagePresentation#updateCachedText()} in a background
+   * thread and then use {@link UsagePresentation#getCachedText()} to draw the text.
+   */
+  @Nullable
+  default TextChunk[] getCachedText() {
+    return getText();
+  }
+
+  default void updateCachedText() {}
+
   @NotNull
   String getPlainText();
 

platform/usageView/src/com/intellij/usages/impl/Node.java

@@ -67,6 +67,8 @@ public abstract class Node extends DefaultMutableTreeNode {
   protected abstract boolean isDataReadOnly();
   protected abstract boolean isDataExcluded();
 
+  protected void updateCachedPresentation() {}
+
   @NotNull
   protected abstract String getText(@NotNull UsageView view);
 
@@ -98,6 +100,7 @@ public abstract class Node extends DefaultMutableTreeNode {
     boolean isDataValid = isDataValid();
     boolean isReadOnly = isDataReadOnly();
     String text = getText(view);
+    updateCachedPresentation();
     doUpdate(edtNodeChangedQueue, isDataValid, isReadOnly, text);
   }
 

platform/usageView/src/com/intellij/usages/impl/UsageNode.java

@@ -93,4 +93,9 @@ public class UsageNode extends Node implements Comparable<UsageNode>, Navigatabl
   protected String getText(@NotNull final UsageView view) {
     return getUsage().getPresentation().getPlainText();
   }
+
+  @Override
+  protected void updateCachedPresentation() {
+    getUsage().getPresentation().updateCachedText();
+  }
 }

platform/usageView/src/com/intellij/usages/impl/UsageViewImpl.java

@@ -1419,7 +1419,7 @@ public class UsageViewImpl implements UsageViewEx {
     }
   }
 
-  private void updateLater() {
+  void updateLater() {
     myUpdateAlarm.cancelAllRequests();
     myUpdateAlarm.addRequest(() -> {
       if (myProject.isDisposed()) return;

platform/usageView/src/com/intellij/usages/impl/UsageViewTreeCellRenderer.java

@@ -49,14 +49,15 @@ class UsageViewTreeCellRenderer extends ColoredTreeCellRenderer {
   private static final SimpleTextAttributes ourNumberOfUsagesAttribute = SimpleTextAttributes.fromTextAttributes(ourColorsScheme.getAttributes(UsageTreeColors.NUMBER_OF_USAGES));
   private static final SimpleTextAttributes ourInvalidAttributesDarcula = new SimpleTextAttributes(null, DarculaColors.RED, null, ourInvalidAttributes.getStyle());
   private static final Insets STANDARD_IPAD_NOWIFI = new Insets(1, 2, 1, 2);
+  private static final TextChunk[] ourLoadingText = {new TextChunk(SimpleTextAttributes.GRAY_ATTRIBUTES.toTextAttributes(), "loading...")};
   private boolean myRowBoundsCalled;
 
   private final UsageViewPresentation myPresentation;
-  private final UsageView myView;
+  private final UsageViewImpl myView;
   private boolean myCalculated;
   private int myRowHeight = AllIcons.Nodes.AbstractClass.getIconHeight()+2;
 
-  UsageViewTreeCellRenderer(@NotNull UsageView view) {
+  UsageViewTreeCellRenderer(@NotNull UsageViewImpl view) {
     myView = view;
     myPresentation = view.getPresentation();
   }
@@ -150,7 +151,16 @@ class UsageViewTreeCellRenderer extends ColoredTreeCellRenderer {
         }
 
         if (node.isValid()) {
-          TextChunk[] text = node.getUsage().getPresentation().getText();
+          TextChunk[] text = node.getUsage().getPresentation().getCachedText();
+          if (text == null) {
+            // either:
+            //   1. the node was never updated yet
+            //   2. the usage presentation have dropped the cached text by itself
+            //      (i.e. it was stored by a soft reference and was gc-ed).
+            //  In either case, `myView.updateLater()` will eventually re-update the visible nodes.
+            text = ourLoadingText;
+            myView.updateLater();
+          }
           for (int i = 0; i < text.length; i++) {
             TextChunk textChunk = text[i];
             SimpleTextAttributes simples = textChunk.getSimpleAttributesIgnoreBackground();