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.bookkeeper.util;
  
  import io.netty.channel.EventLoopGroup;
  import io.netty.channel.SelectStrategy;
  import io.netty.channel.epoll.EpollEventLoopGroup;
  import io.netty.channel.nio.NioEventLoopGroup;
  import io.netty.incubator.channel.uring.IOUring;
  import io.netty.incubator.channel.uring.IOUringEventLoopGroup;
  import java.util.concurrent.ThreadFactory;
  import lombok.experimental.UtilityClass;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.bookkeeper.common.util.affinity.CpuAffinity;
  import org.apache.bookkeeper.conf.ClientConfiguration;
  import org.apache.bookkeeper.conf.ServerConfiguration;
  import org.apache.commons.lang3.StringUtils;
  import org.apache.commons.lang3.SystemUtils;
  
  
  /**
   * Utility class to initialize Netty event loops.
   */
  @Slf4j
  @UtilityClass
  public class EventLoopUtil {
  
      private static final String ENABLE_IO_URING = "enable.io_uring";
  
      public static EventLoopGroup getClientEventLoopGroup(ClientConfiguration conf, ThreadFactory threadFactory) {
          return getEventLoopGroup(threadFactory, conf.getNumIOThreads(), conf.isBusyWaitEnabled());
      }
  
      public static EventLoopGroup getServerEventLoopGroup(ServerConfiguration conf, ThreadFactory threadFactory) {
          return getEventLoopGroup(threadFactory, conf.getServerNumIOThreads(), conf.isBusyWaitEnabled());
      }
  
      public static EventLoopGroup getServerAcceptorGroup(ServerConfiguration conf, ThreadFactory threadFactory) {
          return getEventLoopGroup(threadFactory, conf.getServerNumAcceptorThreads(), false);
      }
  
      private static EventLoopGroup getEventLoopGroup(ThreadFactory threadFactory,
              int numThreads, boolean enableBusyWait) {
          if (!SystemUtils.IS_OS_LINUX) {
              return new NioEventLoopGroup(numThreads, threadFactory);
          }
  
          String enableIoUring = System.getProperty(ENABLE_IO_URING);
  
          // By default, io_uring will not be enabled, even if available. The environment variable will be used:
          // enable.io_uring=1
          if (StringUtils.equalsAnyIgnoreCase(enableIoUring, "1", "true")) {
              // Throw exception if IOUring cannot be used
              IOUring.ensureAvailability();
              return new IOUringEventLoopGroup(numThreads, threadFactory);
          } else {
              try {
                  if (!enableBusyWait) {
                      // Regular Epoll based event loop
                      return new EpollEventLoopGroup(numThreads, threadFactory);
                  }
  
                  // With low latency setting, put the Netty event loop on busy-wait loop to reduce cost of
                  // context switches
                  EpollEventLoopGroup eventLoopGroup = new EpollEventLoopGroup(numThreads, threadFactory,
                          () -> (selectSupplier, hasTasks) -> SelectStrategy.BUSY_WAIT);
  
                  // Enable CPU affinity on IO threads
                  for (int i = 0; i < numThreads; i++) {
                      eventLoopGroup.next().submit(() -> {
                          try {
                              CpuAffinity.acquireCore();
                          } catch (Throwable t) {
                              log.warn("Failed to acquire CPU core for thread {} err {} {}",
                                      Thread.currentThread().getName(), t.getMessage(), t);
                          }
                      });
                  }
  
                  return eventLoopGroup;
              } catch (ExceptionInInitializerError | NoClassDefFoundError | UnsatisfiedLinkError e) {
                  log.warn("Could not use Netty Epoll event loop: {}", e.getMessage());
                  return new NioEventLoopGroup(numThreads, threadFactory);
              }
          }
      }
  }
  