Line data    Source code

       1             : // Copyright (C) 2019 The Android Open Source Project
       2             : //
       3             : // Licensed under the Apache License, Version 2.0 (the "License");
       4             : // you may not use this file except in compliance with the License.
       5             : // You may obtain a copy of the License at
       6             : //
       7             : // http://www.apache.org/licenses/LICENSE-2.0
       8             : //
       9             : // Unless required by applicable law or agreed to in writing, software
      10             : // distributed under the License is distributed on an "AS IS" BASIS,
      11             : // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      12             : // See the License for the specific language governing permissions and
      13             : // limitations under the License.
      14             : 
      15             : package com.google.gerrit.index.query;
      16             : 
      17             : import static java.util.Objects.requireNonNull;
      18             : 
      19             : import com.google.common.collect.ImmutableList;
      20             : import java.util.Iterator;
      21             : import java.util.function.Supplier;
      22             : 
      23             : /**
      24             :  * Result set that allows for asynchronous execution of the actual query. Callers should dispatch
      25             :  * the query and call the constructor of this class with a supplier that fetches the result and
      26             :  * blocks on it if necessary.
      27             :  *
      28             :  * <p>If the execution is synchronous or the results are known a priori, consider using {@link
      29             :  * ListResultSet}.
      30             :  */
      31             : public class LazyResultSet<T> implements ResultSet<T> {
      32             :   private final Supplier<ImmutableList<T>> resultsCallback;
      33             : 
      34         121 :   private boolean resultsReturned = false;
      35             : 
      36         121 :   public LazyResultSet(Supplier<ImmutableList<T>> r) {
      37         121 :     resultsCallback = requireNonNull(r, "results can't be null");
      38         121 :   }
      39             : 
      40             :   @Override
      41             :   public Iterator<T> iterator() {
      42           0 :     return toList().iterator();
      43             :   }
      44             : 
      45             :   @Override
      46             :   public ImmutableList<T> toList() {
      47         121 :     if (resultsReturned) {
      48           0 :       throw new IllegalStateException("Results already obtained");
      49             :     }
      50         121 :     resultsReturned = true;
      51         120 :     return resultsCallback.get();
      52             :   }
      53             : 
      54             :   @Override
      55           0 :   public void close() {}
      56             : 
      57             :   @Override
      58             :   public Object searchAfter() {
      59           0 :     return null;
      60             :   }
      61             : }