drop inmemory caches for unsaved documents on low memory (IDEA-153382)

platform/lang-impl/src/com/intellij/psi/stubs/StubIndexImpl.java

@@ -148,7 +148,7 @@ public class StubIndexImpl extends StubIndex implements ApplicationComponent, Pe
           extension instanceof StringStubIndexExtension && ((StringStubIndexExtension)extension).traceKeyHashToVirtualFileMapping()
         );
 
-        final MemoryIndexStorage<K, StubIdList> memStorage = new MemoryIndexStorage<K, StubIdList>(storage);
+        final MemoryIndexStorage<K, StubIdList> memStorage = new MemoryIndexStorage<K, StubIdList>(storage, indexKey);
         MyIndex<K> index = new MyIndex<>(new IndexExtension<K, StubIdList, Void>() {
           @NotNull
           @Override

platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexImpl.java

@@ -388,7 +388,7 @@ public class FileBasedIndexImpl extends FileBasedIndex {
         }
 
         state.registerIndex(name,
-                            createIndex(extension, new MemoryIndexStorage<K, V>(storage)),
+                            createIndex(extension, new MemoryIndexStorage<K, V>(storage, name)),
                             new FileBasedIndex.InputFilter() {
 
                               @Override

platform/lang-impl/src/com/intellij/util/indexing/MapReduceIndex.java

@@ -76,6 +76,14 @@ public class MapReduceIndex<Key, Value, Input> implements UpdatableIndex<Key,Val
     @Override
     public void run() {
       try {
+        if (myStorage instanceof MemoryIndexStorage) {
+          getWriteLock().lock();
+          try {
+            ((MemoryIndexStorage<Key, Value>)myStorage).clearCaches();
+          } finally {
+            getWriteLock().unlock();
+          }
+        }
         flush();
       } catch (StorageException e) {
         LOG.info(e);

platform/lang-impl/src/com/intellij/util/indexing/MemoryIndexStorage.java

@@ -36,6 +36,7 @@ public class MemoryIndexStorage<Key, Value> implements IndexStorage<Key, Value>
   @NotNull
   private final IndexStorage<Key, Value> myBackendStorage;
   private final List<BufferingStateListener> myListeners = ContainerUtil.createLockFreeCopyOnWriteList();
+  private final ID<?, ?> myIndexId;
   private boolean myBufferingEnabled;
 
   public interface BufferingStateListener {
@@ -45,7 +46,12 @@ public class MemoryIndexStorage<Key, Value> implements IndexStorage<Key, Value>
   }
 
   public MemoryIndexStorage(@NotNull IndexStorage<Key, Value> backend) {
+    this(backend, null);
+  }
+
+  public MemoryIndexStorage(@NotNull IndexStorage<Key, Value> backend, ID<?, ?> indexId) {
     myBackendStorage = backend;
+    myIndexId = indexId;
   }
 
   @NotNull
@@ -85,6 +91,16 @@ public class MemoryIndexStorage<Key, Value> implements IndexStorage<Key, Value>
     }
   }
 
+  void clearCaches() {
+    if (myMap.size() == 0) return;
+    String message = "Dropping caches for " + (myIndexId != null ? myIndexId:this) + ", number of items:" + myMap.size();
+    FileBasedIndexImpl.LOG.info(message);
+
+    for(ChangeTrackingValueContainer<Value> v:myMap.values()) {
+      v.dropMergedData();
+    }
+  }
+
   @Override
   public void close() throws StorageException {
     myBackendStorage.close();