diff --git a/java/compiler/impl/src/com/intellij/compiler/impl/CompileDriver.java b/java/compiler/impl/src/com/intellij/compiler/impl/CompileDriver.java
index d0518ba688e8..51747d7dc732 100644
--- a/java/compiler/impl/src/com/intellij/compiler/impl/CompileDriver.java
+++ b/java/compiler/impl/src/com/intellij/compiler/impl/CompileDriver.java
@@ -220,6 +220,16 @@ public class CompileDriver {
     if (!useOutOfProcessBuild()) {
       scope = addAdditionalRoots(scope, ALL_EXCEPT_SOURCE_PROCESSING);
     }
+    else {
+      final Application app = ApplicationManager.getApplication();
+      if (!app.isUnitTestMode()) {
+        final boolean isDispatchThread = app.isDispatchThread();
+        LOG.assertTrue(!isDispatchThread, "Calling isUpToDate() from Event Dispatch Thread may cause deadlocks");
+        if (isDispatchThread) {
+          return false;
+        }
+      }
+    }
 
     final CompilerTask task = new CompilerTask(myProject, "Classes up-to-date check", true, false);
     final DependencyCache cache = useOutOfProcessBuild()? null : createDependencyCache();
diff --git a/platform/lang-impl/src/com/intellij/codeInsight/completion/StatisticsWeigher.java b/platform/lang-impl/src/com/intellij/codeInsight/completion/StatisticsWeigher.java
index 20f02fc5b320..4fee3f47ab08 100644
--- a/platform/lang-impl/src/com/intellij/codeInsight/completion/StatisticsWeigher.java
+++ b/platform/lang-impl/src/com/intellij/codeInsight/completion/StatisticsWeigher.java
@@ -190,15 +190,35 @@ public class StatisticsWeigher extends CompletionWeigher {
     return info == null ? StatisticsInfo.EMPTY : info;
   }
 
+  /**
+   * For different prefixes we want to prefer different completion items,
+   *   so we decorate their basic stat-infos depending on prefix.
+   * For example, consider that an item "fooBar" was chosen with a prefix "foo"
+   * Then we'll register "fooBar" for each of the sub-prefixes: "", "f", "fo" and "foo"
+   *   and suggest "foobar" whenever we a user types any of those prefixes
+   *
+   * If a user has typed "fooB" for which there's no stat-info registered, we want to check
+   *   all of its sub-prefixes: "", "f", "fo", "foo" and see if any of them is associated with a stat-info
+   * But if the item were "fobia" and the user has typed "fob", we don't want to claim
+   *   that "fooBar" (which matches) is statistically better than "fobia" with prefix "fob" even though both begin with "fo"
+   * So we only check non-partial sub-prefixes, then ones that had been really typed by the user before completing
+   *
+   * @param forWriting controls whether this stat-info will be used for incrementing usage count or for its retrieval (for sorting)
+   */
   public static StatisticsInfo composeStatsWithPrefix(StatisticsInfo info, final String fullPrefix, boolean forWriting) {
     ArrayList<StatisticsInfo> infos = new ArrayList<StatisticsInfo>((fullPrefix.length() + 3) * info.getConjuncts().size());
     for (StatisticsInfo conjunct : info.getConjuncts()) {
       if (forWriting) {
+        // some completion contributors may need pure statistical information to speed up searching for frequently chosen items
         infos.add(conjunct);
       }
       for (int i = 0; i <= fullPrefix.length(); i++) {
+        // if we're incrementing usage count, register all sub-prefixes with "partial" mark
+        // if we're sorting and any sub-prefix was used as non-partial to choose this completion item, prefer it
         infos.add(composeWithPrefix(conjunct, fullPrefix.substring(0, i), forWriting));
       }
+      // if we're incrementing usage count, the full prefix is registered as non-partial
+      // if we're sorting and the current prefix was used as partial sub-prefix to choose this completion item, prefer it
       infos.add(composeWithPrefix(conjunct, fullPrefix, !forWriting));
     }
     return StatisticsInfo.createComposite(infos);