SofterReference

platform/core-impl/src/com/intellij/util/SofterReference.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2000-2012 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.util;
+
+import com.intellij.openapi.util.LowMemoryWatcher;
+import com.intellij.util.containers.WeakList;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+import java.lang.ref.Reference;
+import java.lang.ref.SoftReference;
+import java.lang.ref.WeakReference;
+
+/**
+ * A reference whose referent may be garbage-collected when there's low free memory, not only when there's none.
+ * Use for objects which retain lots of memory and whose loss is not very expensive.
+ *
+ * @author peter
+ */
+public class SofterReference<T> {
+  private volatile Reference<T> myRef;
+  private static final WeakList<SofterReference> ourRegistry = new WeakList<SofterReference>();
+
+  @SuppressWarnings("UnusedDeclaration") private static LowMemoryWatcher ourWatcher = LowMemoryWatcher.register(new Runnable() {
+    @Override
+    public void run() {
+      System.out.println("SofterReference.run: " + ourRegistry.size());
+      for (SofterReference reference : ourRegistry.copyAndClear()) {
+        reference.weaken();
+      }
+    }
+  });
+
+  public SofterReference(@NotNull T referent) {
+    ourRegistry.add(this);
+    myRef = new SoftReference<T>(referent);
+  }
+
+  private void weaken() {
+    T o = myRef.get();
+    if (o != null) {
+      myRef = new WeakReference<T>(o);
+    }
+  }
+
+  @Nullable
+  public T get() {
+    Reference<T> ref = myRef;
+    T referent = ref.get();
+    if (referent != null && ref instanceof WeakReference) {
+      ourRegistry.add(this);
+      myRef = new SoftReference<T>(referent);
+    }
+    return referent;
+  }
+}

platform/util/src/com/intellij/util/containers/WeakList.java

@@ -102,6 +102,15 @@ public class WeakList<T> extends UnsafeWeakList<T> {
     }
   }
 
+  public List<T> copyAndClear() {
+    synchronized (myArray) {
+      List<T> result = new ArrayList<T>(myArray.size());
+      myArray.toStrongCollection(result);
+      clear();
+      return result;
+    }
+  }
+
   private class MySyncIterator extends MyIterator {
     protected void findNext() {
       synchronized (myArray) {