gRPC(Java) keepAlive机制研究

基于java gRPC 1.24.2 分析

结论

gRPC keepAlive是grpc框架在应用层面连接保活的一种措施。即当grpc连接上没有业务数据时，是否发送pingpong,以保持连接活跃性,不因长时间空闲而被Server或操作系统关闭
gRPC keepAlive在client与server都有,client端默认关闭(keepAliveTime为Long.MAX_VALUE), server端默认打开，keepAliveTime为2小时,即每2小时向client发送一次ping

// io.grpc.internal.GrpcUtil

public static final long DEFAULT_SERVER_KEEPALIVE_TIME_NANOS = TimeUnit.HOURS.toNanos(2L);

KeepAlive的管理使用类io.grpc.internal.KeepAliveManager, 用于管理KeepAlive状态，ping任务调度与执行.

Client端KeepAlive

使用入口

我们在使用io.grpc框架创建grpc连接的时候，可以设置keeplive, 例如下面:

NettyChannelBuilder builder = NettyChannelBuilder.forTarget(String.format("grpc://%s", provider)) //

      .usePlaintext() //

      .defaultLoadBalancingPolicy(props.getBalancePolicy()) //

      .maxInboundMessageSize(props.getMaxInboundMessageSize()) //

      .keepAliveTime(1,TimeUnit.MINUTES)

      .keepAliveWithoutCalls(true)

      .keepAliveTimeout(10,TimeUnit.SECONDS)

      .intercept(channelManager.getInterceptors()); //

其中与keepAlive相关的参数有三个,keepAliveTime,keepAliveTimeout,keepAliveWithoutCalls。这三个变量有什么作用呢?

keepAliveTime: 表示当grpc连接没有数据传递时，多久之后开始向server发送ping packet
keepAliveTimeout: 表示当发送完ping packet后多久没收到server回应算超时
keepAliveTimeoutCalls: 表示如果grpc连接没有数据传递时，是否keepAlive,默认为false

简要时序列表

Create & Start

NettyChannelBuilder

   -----> NettyTransportFactory

   ---------> NettyClientTransport

   -------------> KeepAliveManager & NettyClientHandler

响应各种事件

当Active、Idle、DataReceived、Started、Termination事件发生时，更改KeepAlive状态，调度发送ping任务。

Server端KeepAlive

使用入口

// 只截取关键代码,详细代码请看`NettyServerBuilder`

ServerImpl server = new ServerImpl(

    this,

    buildTransportServers(getTracerFactories()),

    Context.ROOT);

for (InternalNotifyOnServerBuild notifyTarget : notifyOnBuildList) {

  notifyTarget.notifyOnBuild(server);

}

return server;

// 在buildTransportServers方法中创建NettyServer

List<NettyServer> transportServers = new ArrayList<>(listenAddresses.size());

for (SocketAddress listenAddress : listenAddresses) {

  NettyServer transportServer = new NettyServer(

      listenAddress, resolvedChannelType, channelOptions, bossEventLoopGroupPool,

      workerEventLoopGroupPool, negotiator, streamTracerFactories,

      getTransportTracerFactory(), maxConcurrentCallsPerConnection, flowControlWindow,

      maxMessageSize, maxHeaderListSize, keepAliveTimeInNanos, keepAliveTimeoutInNanos,

      maxConnectionIdleInNanos, maxConnectionAgeInNanos, maxConnectionAgeGraceInNanos,

      permitKeepAliveWithoutCalls, permitKeepAliveTimeInNanos, getChannelz());

  transportServers.add(transportServer);

}

简要时序列表

Create & Start

NettyServerBuilder

    ---> NettyServer

    ---------> NettyServerTransport

    -------------> NettyServerHandler

    -----------------> KeepAliveEnforcer

连接准备就绪

调用 io.netty.channel.ChannelHandler的handlerAdded方法,关于此方法的描述:

Gets called after the ChannelHandler was added to the actual context and it's ready to handle events.

NettyServerHandler(handlerAdded)

   ---> 创建KeepAliveManager对象

响应各种事件

同Client

KeepAliveEnforcer

在上面Server端的简要时序图中，可以看见，server端有一个特有的io.grpc.netty.KeepAliveEnforcer类

此类的作用是监控clinet ping的频率，以确保其在一个合理范围内。

package io.grpc.netty;

import com.google.common.annotations.VisibleForTesting;

import com.google.common.base.Preconditions;

import java.util.concurrent.TimeUnit;

import javax.annotation.CheckReturnValue;

/** Monitors the client's PING usage to make sure the rate is permitted. */

class KeepAliveEnforcer {

  @VisibleForTesting

  static final int MAX_PING_STRIKES = 2;

  @VisibleForTesting

  static final long IMPLICIT_PERMIT_TIME_NANOS = TimeUnit.HOURS.toNanos(2);

  private final boolean permitWithoutCalls;

  private final long minTimeNanos;

  private final Ticker ticker;

  private final long epoch;

  private long lastValidPingTime;

  private boolean hasOutstandingCalls;

  private int pingStrikes;

  public KeepAliveEnforcer(boolean permitWithoutCalls, long minTime, TimeUnit unit) {

    this(permitWithoutCalls, minTime, unit, SystemTicker.INSTANCE);

  }

  @VisibleForTesting

  KeepAliveEnforcer(boolean permitWithoutCalls, long minTime, TimeUnit unit, Ticker ticker) {

    Preconditions.checkArgument(minTime >= 0, "minTime must be non-negative");

    this.permitWithoutCalls = permitWithoutCalls;

    this.minTimeNanos = Math.min(unit.toNanos(minTime), IMPLICIT_PERMIT_TIME_NANOS);

    this.ticker = ticker;

    this.epoch = ticker.nanoTime();

    lastValidPingTime = epoch;

  }

  /** Returns {@code false} when client is misbehaving and should be disconnected. */

  @CheckReturnValue

  public boolean pingAcceptable() {

    long now = ticker.nanoTime();

    boolean valid;

    if (!hasOutstandingCalls && !permitWithoutCalls) {

      valid = compareNanos(lastValidPingTime + IMPLICIT_PERMIT_TIME_NANOS, now) <= 0;

    } else {

      valid = compareNanos(lastValidPingTime + minTimeNanos, now) <= 0;

    }

    if (!valid) {

      pingStrikes++;

      return !(pingStrikes > MAX_PING_STRIKES);

    } else {

      lastValidPingTime = now;

      return true;

    }

  }

  /**

   * Reset any counters because PINGs are allowed in response to something sent. Typically called

   * when sending HEADERS and DATA frames.

   */

  public void resetCounters() {

    lastValidPingTime = epoch;

    pingStrikes = 0;

  }

  /** There are outstanding RPCs on the transport. */

  public void onTransportActive() {

    hasOutstandingCalls = true;

  }

  /** There are no outstanding RPCs on the transport. */

  public void onTransportIdle() {

    hasOutstandingCalls = false;

  }

  /**

   * Positive when time1 is greater; negative when time2 is greater; 0 when equal. It is important

   * to use something like this instead of directly comparing nano times. See {@link

   * System#nanoTime}.

   */

  private static long compareNanos(long time1, long time2) {

    // Possibility of overflow/underflow is on purpose and necessary for correctness

    return time1 - time2;

  }

  @VisibleForTesting

  interface Ticker {

    long nanoTime();

  }

  @VisibleForTesting

  static class SystemTicker implements Ticker {

    public static final SystemTicker INSTANCE = new SystemTicker();

    @Override

    public long nanoTime() {

      return System.nanoTime();

    }

  }

}

先来看pingAcceptable方法，此方法是判断是否接受client ping。

lastValidPingTime是上次client valid ping的时间, 连接建立时此时间等于KeepAliveEnforcer对象创建的时间。当client ping有效时，其等于当时ping的时间
hasOutstandingCalls其初始值为false，当连接activie时，其值为true,当连接idle时，其值为false。如果grpc调用为阻塞时调用，则调用时连接变为active，调用完成，连接变为idle.
permitWithoutCalls其值是创建NettyServer时传入，默认为false.
IMPLICIT_PERMIT_TIME_NANOS其值为常量，2h
minTimeNanos其值是创建NettyServer时传入，默认为5min.
MAX_PING_STRIKES其值为常量2

resetCounters方法是当grpc当中有数据时会被调用，即有grpc调用时lastValidPingTime和pingStrikes会被重置。
如果client要想使用keepAlive，permitWithoutCalls值需要设置为true，而且cient keepAliveTime需要>=minTimeNanos

巴特西

gRPC(Java) keepAlive机制研究

结论

Client端KeepAlive

使用入口

简要时序列表

Server端KeepAlive

使用入口

简要时序列表

KeepAliveEnforcer

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