memory backed, limited recent strings interner for stubs

platform/core-api/src/com/intellij/psi/stubs/StubSerializationHelper.java

@@ -16,13 +16,15 @@
 package com.intellij.psi.stubs;
 
 import com.intellij.openapi.diagnostic.LogUtil;
-import com.intellij.openapi.diagnostic.Logger;
+import com.intellij.openapi.util.LowMemoryWatcher;
 import com.intellij.openapi.util.io.BufferExposingByteArrayOutputStream;
+import com.intellij.util.containers.SLRUCache;
 import com.intellij.util.io.AbstractStringEnumerator;
 import com.intellij.util.io.DataInputOutputUtil;
 import com.intellij.util.io.IOUtil;
 import gnu.trove.TIntObjectHashMap;
 import gnu.trove.TObjectIntHashMap;
+import jsr166e.SequenceLock;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -32,13 +34,12 @@ import java.io.InputStream;
 import java.io.OutputStream;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.locks.Lock;
 
 /**
  * Author: dmitrylomov
  */
 public class StubSerializationHelper {
-  private static final Logger LOG = Logger.getInstance("#com.intellij.psi.stubs.StubSerializationHelper");
-
   private AbstractStringEnumerator myNameStorage;
 
   protected final TIntObjectHashMap<StubSerializer<? extends StubElement>> myIdToSerializer = new TIntObjectHashMap<StubSerializer<? extends StubElement>>();
@@ -47,6 +48,7 @@ public class StubSerializationHelper {
   public StubSerializationHelper(AbstractStringEnumerator nameStorage) {
     myNameStorage = nameStorage;
   }
+
   public void assignId(@NotNull final StubSerializer<? extends StubElement> serializer) throws IOException {
     final int id = persistentId(serializer);
     final StubSerializer old = myIdToSerializer.put(id, serializer);
@@ -98,6 +100,58 @@ public class StubSerializationHelper {
     return idValue;
   }
 
+  private static class RecentStringInterner {
+    private final int myStripeMask;
+    private final SLRUCache<String, String>[] myInterns;
+    private final Lock[] myStripeLocks;
+    private final LowMemoryWatcher myClearingCallback;
+
+    private RecentStringInterner(int capacity) {
+      final int stripes = 16;
+      myInterns = new SLRUCache[stripes];
+      myStripeLocks = new Lock[myInterns.length];
+      for(int i = 0; i < myInterns.length; ++i) {
+        myInterns[i] = new SLRUCache<String, String>(capacity / stripes, capacity / stripes) {
+          @NotNull
+          @Override
+          public String createValue(String key) {
+            return key;
+          }
+        };
+        myStripeLocks[i] = new SequenceLock();
+      }
+
+      assert Integer.highestOneBit(stripes) == stripes;
+      myStripeMask = stripes - 1;
+      myClearingCallback = LowMemoryWatcher.register(new Runnable() {
+        @Override
+        public void run() {
+          clear();
+        };
+      });
+    }
+
+    String get(String s) {
+      final int stripe = Math.abs(s.hashCode()) & myStripeMask;
+      try {
+        myStripeLocks[stripe].lock();
+        return myInterns[stripe].get(s);
+      } finally {
+        myStripeLocks[stripe].unlock();
+      }
+    }
+
+    void clear() {
+      for(int i = 0; i < myInterns.length; ++i) {
+        myStripeLocks[i].lock();
+        myInterns[i].clear();
+        myStripeLocks[i].unlock();
+      }
+    }
+  }
+
+  private final RecentStringInterner myStringInterner = new RecentStringInterner(8192);
+
   public StubElement deserialize(InputStream stream) throws IOException {
     FileLocalStringEnumerator storage = new FileLocalStringEnumerator();
     StubInputStream inputStream = new StubInputStream(stream, storage);
@@ -106,7 +160,7 @@ public class StubSerializationHelper {
 
     int i = 1;
     while(i <= size) {
-      String s = IOUtil.readUTFFast(buffer, inputStream);
+      String s = myStringInterner.get(IOUtil.readUTFFast(buffer, inputStream));
       storage.myStrings.add(s);
       storage.myEnumerates.put(s, i);
       ++i;