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balance_ketama.go
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balance_ketama.go
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package grpclb
import (
"errors"
"hash/fnv"
"math"
"sort"
"strconv"
"sync"
"sync/atomic"
"golang.org/x/net/context"
"google.golang.org/grpc"
"google.golang.org/grpc/grpclog"
"google.golang.org/grpc/naming"
)
type ketamaBalance struct {
sync.RWMutex
servers map[string]*server
replica map[uint32]*server
sortedHashSet []uint32
addrsCh chan []grpc.Address
waitCh chan struct{}
done bool
f HasherFromContext
r naming.Resolver
w naming.Watcher
}
// NewKetamaBalance balance with ketama algorithm.
func NewKetamaBalance(r naming.Resolver, f ...HasherFromContext) grpc.Balancer {
kb := &ketamaBalance{
servers: map[string]*server{},
replica: map[uint32]*server{},
sortedHashSet: []uint32{},
addrsCh: make(chan []grpc.Address, 1),
waitCh: make(chan struct{}),
r: r,
}
if len(f) > 0 {
kb.f = f[0]
} else {
kb.f = strOrNumFromContext
}
return kb
}
func (kb *ketamaBalance) add(s *server) {
addr := s.addr.Addr
if _, ok := kb.servers[addr]; ok {
grpclog.Printf("grpclb: The name resolver added an exisited server(%s).\n", addr)
return
}
w := weightFromMetadata(s.addr.Metadata)
step := math.MaxUint32 / w
kb.servers[addr] = s
h := fnv.New32a()
h.Write([]byte(addr))
serverHash := h.Sum32()
h.Reset()
for i := 1; i <= int(w); i++ {
h.Write([]byte(strconv.FormatUint(uint64(serverHash)+uint64(i)*uint64(step), 10)))
tmpH := h.Sum32()
kb.sortedHashSet = append(kb.sortedHashSet, tmpH)
kb.replica[tmpH] = s
h.Reset()
}
sort.Slice(kb.sortedHashSet, func(i int, j int) bool {
return kb.sortedHashSet[i] < kb.sortedHashSet[j]
})
}
func (kb *ketamaBalance) delHash(h uint32) {
for i, v := range kb.sortedHashSet {
if v == h {
kb.sortedHashSet = append(kb.sortedHashSet[:i], kb.sortedHashSet[i+1:]...)
return
}
}
}
func (kb *ketamaBalance) delete(addr string) {
s, ok := kb.servers[addr]
if !ok {
grpclog.Printf("grpclb: The name resolver deleted an unexistd server(%s).\n", addr)
return
}
delete(kb.servers, addr)
for k, v := range kb.replica {
if v == s {
delete(kb.replica, k)
kb.delHash(k)
}
}
}
func (kb *ketamaBalance) get(ctx context.Context) (*server, error) {
h, ok := kb.f(ctx)
if !ok {
return nil, errors.New("grpclb: The HashKey is not in the context")
}
length := len(kb.sortedHashSet)
if length == 0 {
return nil, ErrNoServer
}
hash32 := h.Hash32()
idx := sort.Search(length, func(i int) bool {
return kb.sortedHashSet[i] >= hash32
})
if idx >= length {
idx = 0
}
return kb.replica[kb.sortedHashSet[idx]], nil
}
func (kb *ketamaBalance) watchAddrUpdates() error {
us, err := kb.w.Next()
if err != nil {
grpclog.Printf("grpclb: The naming watcher stops working due to error(%v).\n", err)
return err
}
kb.Lock()
defer kb.Unlock()
for _, u := range us {
switch u.Op {
case naming.Add:
kb.add(&server{addr: grpc.Address{Addr: u.Addr, Metadata: u.Metadata}})
case naming.Delete:
kb.delete(u.Addr)
default:
grpclog.Printf("grpclb: The name resolver provided an unsupported operation(%v).\n", u)
}
}
if len(kb.servers) == 0 {
if kb.waitCh == nil {
kb.waitCh = make(chan struct{})
}
} else {
if kb.waitCh != nil {
close(kb.waitCh)
kb.waitCh = nil
}
}
select {
case <-kb.addrsCh:
default:
}
var as []grpc.Address
for _, s := range kb.servers {
as = append(as, s.addr)
}
kb.addrsCh <- as
return nil
}
func (kb *ketamaBalance) Start(target string, _ grpc.BalancerConfig) (err error) {
kb.Lock()
defer kb.Unlock()
if kb.done {
return grpc.ErrClientConnClosing
}
if kb.w, err = kb.r.Resolve(target); err != nil {
return
}
go func() {
for {
if err := kb.watchAddrUpdates(); err != nil {
return
}
}
}()
return
}
func (kb *ketamaBalance) Up(addr grpc.Address) (down func(error)) {
kb.RLock()
defer kb.RUnlock()
if server, ok := kb.servers[addr.Addr]; ok {
server.connected.Set()
}
return func(err error) {
kb.RLock()
defer kb.RUnlock()
grpclog.Errorf("grpclb: The connection to(%s) is lost due to error(%v).\n", addr.Addr, err)
if server, ok := kb.servers[addr.Addr]; ok {
server.connected.UnSet()
}
}
}
func (kb *ketamaBalance) Get(ctx context.Context, opts grpc.BalancerGetOptions) (addr grpc.Address, put func(), err error) {
if opts.BlockingWait {
kb.RLock()
ch := kb.waitCh
kb.RUnlock()
if ch != nil {
select {
case <-ctx.Done():
err = ctx.Err()
case <-ch:
// wait util there is a new registry server.
}
}
}
kb.RLock()
defer kb.RUnlock()
if kb.done {
err = grpc.ErrClientConnClosing
return
}
s, err := kb.get(ctx)
if err != nil {
return
}
addr = s.addr
atomic.AddUint64(&s.currConns, 1)
put = func() {
kb.RLock()
defer kb.RUnlock()
if s != nil {
atomic.AddUint64(&s.currConns, ^uint64(0))
}
}
return
}
func (kb *ketamaBalance) Notify() <-chan []grpc.Address {
return kb.addrsCh
}
func (kb *ketamaBalance) Close() error {
kb.Lock()
defer kb.Unlock()
if kb.done {
return errors.New("grpclb: Balancer is closed")
}
if kb.w != nil {
kb.w.Close()
}
if kb.waitCh != nil {
close(kb.waitCh)
kb.waitCh = nil
}
if kb.addrsCh != nil {
close(kb.addrsCh)
}
return nil
}