content: /*
   * Licensed to the Apache Software Foundation (ASF) under one
   * or more contributor license agreements.  See the NOTICE file
   * distributed with this work for additional information
   * regarding copyright ownership.  The ASF licenses this file
   * to you 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 org.apache.beam.runners.fnexecution.control;
  
  import java.time.Duration;
  import java.util.Map;
  import java.util.concurrent.CompletableFuture;
  import java.util.concurrent.ExecutionException;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.TimeoutException;
  import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Maps;
  
  /**
   * A {@link ControlClientPool} backed by a client map. It is expected that a given client id will be
   * requested at most once.
   */
  public class MapControlClientPool implements ControlClientPool {
  
    /** Creates a {@link MapControlClientPool}. */
    public static MapControlClientPool create() {
      return new MapControlClientPool();
    }
  
    private final Map<String, CompletableFuture<InstructionRequestHandler>> clients =
        Maps.newConcurrentMap();
  
    private MapControlClientPool() {}
  
    @Override
    public Source getSource() {
      return this::getClient;
    }
  
    @Override
    public Sink getSink() {
      return this::putClient;
    }
  
    private void putClient(String workerId, InstructionRequestHandler client) {
      CompletableFuture<InstructionRequestHandler> future =
          clients.computeIfAbsent(workerId, MapControlClientPool::createClientFuture);
      boolean success = future.complete(client);
      if (!success) {
        throw new IllegalStateException(
            String.format("Control client for worker id %s failed to compete", workerId));
      }
    }
  
    private InstructionRequestHandler getClient(String workerId, Duration timeout)
        throws ExecutionException, InterruptedException, TimeoutException {
      CompletableFuture<InstructionRequestHandler> future =
          clients.computeIfAbsent(workerId, MapControlClientPool::createClientFuture);
      // TODO: Wire in health checking of clients so requests don't hang.
      future.get(timeout.getSeconds(), TimeUnit.SECONDS);
      InstructionRequestHandler client = future.get();
      clients.remove(workerId);
      return client;
    }
  
    private static CompletableFuture<InstructionRequestHandler> createClientFuture(String unused) {
      return new CompletableFuture<>();
    }
  }
  