balancer.go

package clientv3

import (

    "net/url"

    "strings"

    "sync"

    "golang.org/x/net/context"

    "google.golang.org/grpc"

    "google.golang.org/grpc/codes"

// ErrNoAddrAvilable is returned by Get() when the balancer does not have

// any active connection to endpoints at the time.

// This error is returned only when opts.BlockingWait is true.

var ErrNoAddrAvilable = grpc.Errorf(codes.Unavailable, "there is no address available")

// simpleBalancer does the bare minimum to expose multiple eps

// to the grpc reconnection code path

//简单均衡器

type simpleBalancer struct {

    // addrs are the client's endpoints for grpc

    addrs []grpc.Address  //nsqd 地址列表

    // notifyCh notifies grpc of the set of addresses for connecting

    notifyCh chan []grpc.Address  //链接通知地址

    // readyc closes once the first connection is up

//一旦连接上 ，就关闭链接  并且 只执行一次

    readyc    chan struct{}

    readyOnce sync.Once

    // mu protects upEps, pinAddr, and connectingAddr

    //锁  保护 upEps, pinAddr, and connectingAddr 的锁

    mu sync.RWMutex

    // upEps holds the current endpoints that have an active connection

//已经存活的链接地址

    upEps map[string]struct{}

    // upc closes when upEps transitions from empty to non-zero or the balancer closes.

//当upEps为空 转化为非空 或者均衡器关闭的时候 ，关闭此通道

    upc chan struct{}

    // grpc issues TLS cert checks using the string passed into dial so

    // that string must be the host. To recover the full scheme://host URL,

    // have a map from hosts to the original endpoint.

//host 到 endpoint 映射 map集合

    host2ep map[string]string

    // pinAddr is the currently pinned address; set to the empty string on

    // intialization and shutdown.

//当前固定的地址。当此变量被初始化或者关闭的时候  设置为空

    pinAddr string

//是否关闭的标志

    closed bool

//创建负载均衡器

func newSimpleBalancer(eps []string) *simpleBalancer {

    notifyCh := make(chan []grpc.Address, 1)

    addrs := make([]grpc.Address, len(eps))

    for i := range eps {

        addrs[i].Addr = getHost(eps[i])

    notifyCh <- addrs

    sb := &simpleBalancer{

        addrs:    addrs,

        notifyCh: notifyCh,

        readyc:   make(chan struct{}),

        upEps:    make(map[string]struct{}),

        upc:      make(chan struct{}),

        host2ep:  getHost2ep(eps),

    return sb

//启动

func (b *simpleBalancer) Start(target string, config grpc.BalancerConfig) error { return nil }

//链接通知

func (b *simpleBalancer) ConnectNotify() <-chan struct{} {

    b.mu.Lock()

    defer b.mu.Unlock()

    return b.upc

//通过主机 转化为地址

func (b *simpleBalancer) getEndpoint(host string) string {

    b.mu.Lock()

    defer b.mu.Unlock()

    return b.host2ep[host]

//同上相反

func getHost2ep(eps []string) map[string]string {

    hm := make(map[string]string, len(eps))

    for i := range eps {

        _, host, _ := parseEndpoint(eps[i])

        hm[host] = eps[i]

    return hm

//更新地址列表

func (b *simpleBalancer) updateAddrs(eps []string) {

    np := getHost2ep(eps)

    b.mu.Lock()

    defer b.mu.Unlock()

    match := len(np) == len(b.host2ep)

    for k, v := range np {

        if b.host2ep[k] != v {

            match = false

            break

    if match {

        // same endpoints, so no need to update address

        return

    b.host2ep = np

    addrs := make([]grpc.Address, 0, len(eps))

    for i := range eps {

        addrs = append(addrs, grpc.Address{Addr: getHost(eps[i])})

    b.addrs = addrs

    b.notifyCh <- addrs

//运行中的机器

func (b *simpleBalancer) Up(addr grpc.Address) func(error) {

    b.mu.Lock()

    defer b.mu.Unlock()

    // gRPC might call Up after it called Close. We add this check

    // to "fix" it up at application layer. Or our simplerBalancer

    // might panic since b.upc is closed.

    if b.closed {

        return func(err error) {}

    if len(b.upEps) == 0 {

        // notify waiting Get()s and pin first connected address

        close(b.upc)

        b.pinAddr = addr.Addr

    b.upEps[addr.Addr] = struct{}{}

    // notify client that a connection is up

    b.readyOnce.Do(func() { close(b.readyc) })

    return func(err error) {

        b.mu.Lock()

        delete(b.upEps, addr.Addr)

        if len(b.upEps) == 0 && b.pinAddr != "" {

            b.upc = make(chan struct{})

        } else if b.pinAddr == addr.Addr {

            // choose new random up endpoint

            for k := range b.upEps {

                b.pinAddr = k

                break

        b.mu.Unlock()

func (b *simpleBalancer) Get(ctx context.Context, opts grpc.BalancerGetOptions) (grpc.Address, func(), error) {

    var addr string

    // If opts.BlockingWait is false (for fail-fast RPCs), it should return

    // an address it has notified via Notify immediately instead of blocking.

    if !opts.BlockingWait {

        b.mu.RLock()

        closed := b.closed

        addr = b.pinAddr

        upEps := len(b.upEps)

        b.mu.RUnlock()

        if closed {

            return grpc.Address{Addr: ""}, nil, grpc.ErrClientConnClosing

        if upEps == 0 {

            return grpc.Address{Addr: ""}, nil, ErrNoAddrAvilable

        return grpc.Address{Addr: addr}, func() {}, nil

    for {

        b.mu.RLock()

        ch := b.upc

        b.mu.RUnlock()

        select {

        case <-ch:

        case <-ctx.Done():

            return grpc.Address{Addr: ""}, nil, ctx.Err()

        b.mu.RLock()

        addr = b.pinAddr

        upEps := len(b.upEps)

        b.mu.RUnlock()

        if addr == "" {

            return grpc.Address{Addr: ""}, nil, grpc.ErrClientConnClosing

        if upEps > 0 {

            break

    return grpc.Address{Addr: addr}, func() {}, nil

func (b *simpleBalancer) Notify() <-chan []grpc.Address { return b.notifyCh }

func (b *simpleBalancer) Close() error {

    b.mu.Lock()

    defer b.mu.Unlock()

    // In case gRPC calls close twice. TODO: remove the checking

    // when we are sure that gRPC wont call close twice.

    if b.closed {

        return nil

    b.closed = true

    close(b.notifyCh)

    // terminate all waiting Get()s

    b.pinAddr = ""

    if len(b.upEps) == 0 {

        close(b.upc)

    return nil

func getHost(ep string) string {

    url, uerr := url.Parse(ep)

    if uerr != nil || !strings.Contains(ep, "://") {

        return ep

    return url.Host

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