// 连接池, 通过 host 区分不同的池private final ConcurrentHashMap<String, ConcurrentLinkedQueue<IdleChannel>> connectionsPool = new ConcurrentHashMap<String, ConcurrentLinkedQueue<IdleChannel>>();// 原生channel跟IdleChannel对象的映射, IdleChannel主要是包含一些请求信息, 请求url以及请求开始时间private final ConcurrentHashMap<Channel, IdleChannel> channel2IdleChannel = new ConcurrentHashMap<Channel, IdleChannel>();// 记录了Channel的创建时间, 用于做Channel生命周期检测, 如果生命周期是-1, 此Map无用private final ConcurrentHashMap<Channel, Long> channel2CreationDate = new ConcurrentHashMap<Channel, Long>();

synchronized (idleConnectionForHost) {idleChannel = idleConnectionForHost.poll();if (idleChannel != null) {channel2IdleChannel.remove(idleChannel.channel);}
}

    public boolean canCacheConnection() {if (!isClosed.get() && maxTotalConnections != -1 && channel2IdleChannel.size() >= maxTotalConnections) {return false;} else {return true;}}

// Do not throw an exception when we need an extra connection for a redirect.if (!reclaimCache && !connectionsPool.canCacheConnection()) {IOException ex = new IOException(String.format("Too many connections %s", config.getMaxTotalConnections()));try {asyncHandler.onThrowable(ex);} catch (Throwable t) {log.warn("!connectionsPool.canCacheConnection()", t);}throw ex;}

    if (trackConnections) {if (!reclaimCache) {if (!freeConnections.tryAcquire()) {IOException ex = new IOException(String.format("Too many connections %s", config.getMaxTotalConnections()));try {asyncHandler.onThrowable(ex);} catch (Throwable t) {log.warn("!connectionsPool.canCacheConnection()", t);}throw ex;} else {acquiredConnection = true;}}}

    private void finishUpdate(final NettyResponseFuture<?> future, final ChannelHandlerContext ctx, boolean lastValidChunk) throws IOException {if (lastValidChunk && future.getKeepAlive()) {drainChannel(ctx, future);} else {if (future.getKeepAlive() && ctx.getChannel().isReadable() && connectionsPool.offer(getPoolKey(future), ctx.getChannel())) {markAsDone(future, ctx);return;}finishChannel(ctx);}markAsDone(future, ctx);}