/*
 * 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.openapi.compiler;

import com.intellij.openapi.util.Key;
import com.intellij.openapi.util.UserDataHolderBase;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;

import java.util.*;

public class ExportableUserDataHolderBase extends UserDataHolderBase implements ExportableUserDataHolder{
  private final Set<Key> myKeys = Collections.synchronizedSet(new HashSet<Key>());

  @NotNull
  public final Map<Key, Object> exportUserData() {
    final Map<Key, Object> result = new HashMap<Key, Object>();
    synchronized (myKeys) {
      for (Key<?> k : myKeys) {
        final Object data = getUserData(k);
        if (data != null) {
          result.put(k, data);
        }
      }
    }
    return result;
  }

  @Override
  public final <T> void putUserData(@NotNull Key<T> key, @Nullable T value) {
    if (value != null) {
      myKeys.add(key);
    }
    else {
      myKeys.remove(key);
    }
    super.putUserData(key, value);
  }

}

/*
 * 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.openapi.compiler;

import com.intellij.openapi.util.Key;
import com.intellij.openapi.util.UserDataHolderBase;
import com.intellij.util.keyFMap.KeyFMap;
import org.jetbrains.annotations.NotNull;

import java.util.HashMap;
import java.util.Map;

public class ExportableUserDataHolderBase extends UserDataHolderBase implements ExportableUserDataHolder{
  @NotNull
  public final Map<Key, Object> exportUserData() {
    final Map<Key, Object> result = new HashMap<Key, Object>();

    KeyFMap map = getUserMap();
    Key[] keys = map.getKeys();

    for (Key<?> k : keys) {
      final Object data = map.get(k);
      if (data != null) {
        result.put(k, data);
      }
    }

    return result;
  }
}

Use KeyFMap#getKeys in ExportableUserDataHolderBase to simplify and improve performance