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/*
 * Tencent is pleased to support the open source community by making Angel available.
 *
 * Copyright (C) 2017-2018 THL A29 Limited, a Tencent company. All rights reserved.
 *
 * 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
 *
 * https://opensource.org/licenses/Apache-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.tencent.angel.ipc;

import io.netty.buffer.PooledByteBufAllocator;
import io.netty.channel.Channel;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.ServerChannel;
import io.netty.channel.epoll.EpollEventLoopGroup;
import io.netty.channel.epoll.EpollServerSocketChannel;
import io.netty.channel.epoll.EpollSocketChannel;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.LengthFieldBasedFrameDecoder;
import io.netty.util.concurrent.DefaultThreadFactory;
import io.netty.util.internal.PlatformDependent;

import java.lang.reflect.Field;
import java.util.concurrent.ThreadFactory;

/**
 * Utilities for creating various Netty constructs based on whether we're using EPOLL or NIO.
 */
public class NettyUtils {
  /**
   * Creates a new ThreadFactory which prefixes each thread with the given name.
   */
  public static ThreadFactory createThreadFactory(String threadPoolPrefix) {
    return new DefaultThreadFactory(threadPoolPrefix, true);
  }

  /**
   * Creates a Netty EventLoopGroup based on the IOMode.
   */
  public static EventLoopGroup createEventLoop(IOMode mode, int numThreads, String threadPrefix) {
    ThreadFactory threadFactory = createThreadFactory(threadPrefix);

    switch (mode) {
      case NIO:
        return new NioEventLoopGroup(numThreads, threadFactory);
      case EPOLL:
        return new EpollEventLoopGroup(numThreads, threadFactory);
      default:
        throw new IllegalArgumentException("Unknown io mode: " + mode);
    }
  }

  /**
   * Returns the correct (client) SocketChannel class based on IOMode.
   */
  public static Class getClientChannelClass(IOMode mode) {
    switch (mode) {
      case NIO:
        return NioSocketChannel.class;
      case EPOLL:
        return EpollSocketChannel.class;
      default:
        throw new IllegalArgumentException("Unknown io mode: " + mode);
    }
  }

  /**
   * Returns the correct ServerSocketChannel class based on IOMode.
   */
  public static Class getServerChannelClass(IOMode mode) {
    switch (mode) {
      case NIO:
        return NioServerSocketChannel.class;
      case EPOLL:
        return EpollServerSocketChannel.class;
      default:
        throw new IllegalArgumentException("Unknown io mode: " + mode);
    }
  }

  /**
   * Creates a LengthFieldBasedFrameDecoder where the first 8 bytes are the length of the frame.
   * This is used before all decoders.
   */
  public static ByteToMessageDecoder createFrameDecoder() {
    // maxFrameLength = 2G
    // lengthFieldOffset = 0
    // lengthFieldLength = 8
    // lengthAdjustment = -8, i.e. exclude the 8 byte length itself
    // initialBytesToStrip = 8, i.e. strip out the length field itself
    return new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 8, -8, 8);
  }

  /**
   * Returns the remote address on the channel or "<unknown remote>" if none exists.
   */
  public static String getRemoteAddress(Channel channel) {
    if (channel != null && channel.remoteAddress() != null) {
      return channel.remoteAddress().toString();
    }
    return "";
  }

  /**
   * Create a pooled ByteBuf allocator but disables the thread-local cache. Thread-local caches
   * are disabled for TransportClients because the ByteBufs are allocated by the event loop thread,
   * but released by the executor thread rather than the event loop thread. Those thread-local
   * caches actually delay the recycling of buffers, leading to larger memory usage.
   */
  public static PooledByteBufAllocator createPooledByteBufAllocator(boolean allowDirectBufs,
    boolean allowCache, int numCores) {
    if (numCores == 0) {
      numCores = Runtime.getRuntime().availableProcessors();
    }
    return new PooledByteBufAllocator(allowDirectBufs && PlatformDependent.directBufferPreferred(),
      Math.min(getPrivateStaticField("DEFAULT_NUM_HEAP_ARENA"), numCores),
      Math.min(getPrivateStaticField("DEFAULT_NUM_DIRECT_ARENA"), allowDirectBufs ? numCores : 0),
      getPrivateStaticField("DEFAULT_PAGE_SIZE"), getPrivateStaticField("DEFAULT_MAX_ORDER"),
      allowCache ? getPrivateStaticField("DEFAULT_TINY_CACHE_SIZE") : 0,
      allowCache ? getPrivateStaticField("DEFAULT_SMALL_CACHE_SIZE") : 0,
      allowCache ? getPrivateStaticField("DEFAULT_NORMAL_CACHE_SIZE") : 0);
  }

  /**
   * Used to get defaults from Netty's private static fields.
   */
  private static int getPrivateStaticField(String name) {
    try {
      Field f = PooledByteBufAllocator.DEFAULT.getClass().getDeclaredField(name);
      f.setAccessible(true);
      return f.getInt(null);
    } catch (Exception e) {
      throw new RuntimeException(e);
    }
  }
}