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

/*
 * Copyright 2000-2013 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.containers;

import org.jetbrains.annotations.NotNull;

import java.util.Collection;
import java.util.Iterator;
import java.util.List;

/**
 * Implementation of the {@link List} interface which:
 * <ul>
 *   <li>Stores elements using weak semantics (see {@link java.lang.ref.WeakReference})</li>
 *   <li>Automatically reclaims storage for garbage collected elements</li>
 *   <li>Is thread safe</li>
 *   <li>Is NOT RandomAccess, because garbage collector can remove element at any time</li>
 *   <li>Does NOT support null elements</li>
 * </ul>
 */
public class WeakList<T> extends UnsafeWeakList<T> {
  @Override
  public boolean add(@NotNull T element) {
    synchronized (myList) {
      return super.add(element);
    }
  }

  @Override
  public boolean addAll(@NotNull Collection<? extends T> c) {
    synchronized (myList) {
      return super.addAll(c);
    }
  }

  @Override
  public boolean addIfAbsent(@NotNull T element) {
    synchronized (myList) {
      return super.addIfAbsent(element);
    }
  }

  @Override
  public void clear() {
    synchronized (myList) {
      super.clear();
    }
  }

  @Override
  public boolean contains(@NotNull Object o) {
    synchronized (myList) {
      return super.contains(o);
    }
  }

  @Override
  public boolean remove(@NotNull Object o) {
    synchronized (myList) {
      return super.remove(o);
    }
  }

  @Override
  public boolean removeAll(@NotNull Collection<?> c) {
    synchronized (myList) {
      return super.removeAll(c);
    }
  }

  @Override
  public boolean isEmpty() {
    synchronized (myList) {
      return super.isEmpty();
    }
  }

  @Override
  @NotNull
  public Iterator<T> iterator() {
    final Iterator<T> iterator;
    synchronized (myList) {
      iterator = super.iterator();
    }
    return new Iterator<T>(){
      @Override
      public boolean hasNext() {
        synchronized (myList) {
          return iterator.hasNext();
        }
      }

      @Override
      public T next() {
        synchronized (myList) {
          return iterator.next();
        }
      }

      @Override
      public void remove() {
        synchronized (myList) {
          iterator.remove();
        }
      }
    };
  }

  @NotNull
  @Override
  public List<T> toStrongList() {
    synchronized (myList) {
      return super.toStrongList();
    }
  }

  @NotNull
  public List<T> copyAndClear() {
    synchronized (myList) {
      List<T> result = toStrongList();
      clear();
      return result;
    }
  }
}