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/*
*
* Copyright 2016 gRPC authors.
*
* 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
*
* http://www.apache.org/licenses/LICENSE-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 grpc
import (
"context"
"net"
"sync"
"google.golang.org/grpc/codes"
"google.golang.org/grpc/credentials"
"google.golang.org/grpc/grpclog"
"google.golang.org/grpc/naming"
"google.golang.org/grpc/status"
)
// Address represents a server the client connects to.
//
// Deprecated: please use package balancer.
type Address struct {
// Addr is the server address on which a connection will be established.
Addr string
// Metadata is the information associated with Addr, which may be used
// to make load balancing decision.
Metadata interface{}
}
// BalancerConfig specifies the configurations for Balancer.
//
// Deprecated: please use package balancer.
type BalancerConfig struct {
// DialCreds is the transport credential the Balancer implementation can
// use to dial to a remote load balancer server. The Balancer implementations
// can ignore this if it does not need to talk to another party securely.
DialCreds credentials.TransportCredentials
// Dialer is the custom dialer the Balancer implementation can use to dial
// to a remote load balancer server. The Balancer implementations
// can ignore this if it doesn't need to talk to remote balancer.
Dialer func(context.Context, string) (net.Conn, error)
}
// BalancerGetOptions configures a Get call.
//
// Deprecated: please use package balancer.
type BalancerGetOptions struct {
// BlockingWait specifies whether Get should block when there is no
// connected address.
BlockingWait bool
}
// Balancer chooses network addresses for RPCs.
//
// Deprecated: please use package balancer.
type Balancer interface {
// Start does the initialization work to bootstrap a Balancer. For example,
// this function may start the name resolution and watch the updates. It will
// be called when dialing.
Start(target string, config BalancerConfig) error
// Up informs the Balancer that gRPC has a connection to the server at
// addr. It returns down which is called once the connection to addr gets
// lost or closed.
// TODO: It is not clear how to construct and take advantage of the meaningful error
// parameter for down. Need realistic demands to guide.
Up(addr Address) (down func(error))
// Get gets the address of a server for the RPC corresponding to ctx.
// i) If it returns a connected address, gRPC internals issues the RPC on the
// connection to this address;
// ii) If it returns an address on which the connection is under construction
// (initiated by Notify(...)) but not connected, gRPC internals
// * fails RPC if the RPC is fail-fast and connection is in the TransientFailure or
// Shutdown state;
// or
// * issues RPC on the connection otherwise.
// iii) If it returns an address on which the connection does not exist, gRPC
// internals treats it as an error and will fail the corresponding RPC.
//
// Therefore, the following is the recommended rule when writing a custom Balancer.
// If opts.BlockingWait is true, it should return a connected address or
// block if there is no connected address. It should respect the timeout or
// cancellation of ctx when blocking. If opts.BlockingWait is false (for fail-fast
// RPCs), it should return an address it has notified via Notify(...) immediately
// instead of blocking.
//
// The function returns put which is called once the rpc has completed or failed.
// put can collect and report RPC stats to a remote load balancer.
//
// This function should only return the errors Balancer cannot recover by itself.
// gRPC internals will fail the RPC if an error is returned.
Get(ctx context.Context, opts BalancerGetOptions) (addr Address, put func(), err error)
// Notify returns a channel that is used by gRPC internals to watch the addresses
// gRPC needs to connect. The addresses might be from a name resolver or remote
// load balancer. gRPC internals will compare it with the existing connected
// addresses. If the address Balancer notified is not in the existing connected
// addresses, gRPC starts to connect the address. If an address in the existing
// connected addresses is not in the notification list, the corresponding connection
// is shutdown gracefully. Otherwise, there are no operations to take. Note that
// the Address slice must be the full list of the Addresses which should be connected.
// It is NOT delta.
Notify() <-chan []Address
// Close shuts down the balancer.
Close() error
}
// RoundRobin returns a Balancer that selects addresses round-robin. It uses r to watch
// the name resolution updates and updates the addresses available correspondingly.
//
// Deprecated: please use package balancer/roundrobin.
func RoundRobin(r naming.Resolver) Balancer {
return &roundRobin{r: r}
}
type addrInfo struct {
addr Address
connected bool
}
type roundRobin struct {
r naming.Resolver
w naming.Watcher
addrs []*addrInfo // all the addresses the client should potentially connect
mu sync.Mutex
addrCh chan []Address // the channel to notify gRPC internals the list of addresses the client should connect to.
next int // index of the next address to return for Get()
waitCh chan struct{} // the channel to block when there is no connected address available
done bool // The Balancer is closed.
}
func (rr *roundRobin) watchAddrUpdates() error {
updates, err := rr.w.Next()
if err != nil {
grpclog.Warningf("grpc: the naming watcher stops working due to %v.", err)
return err
}
rr.mu.Lock()
defer rr.mu.Unlock()
for _, update := range updates {
addr := Address{
Addr: update.Addr,
Metadata: update.Metadata,
}
switch update.Op {
case naming.Add:
var exist bool
for _, v := range rr.addrs {
if addr == v.addr {
exist = true
grpclog.Infoln("grpc: The name resolver wanted to add an existing address: ", addr)
break
}
}
if exist {
continue
}
rr.addrs = append(rr.addrs, &addrInfo{addr: addr})
case naming.Delete:
for i, v := range rr.addrs {
if addr == v.addr {
copy(rr.addrs[i:], rr.addrs[i+1:])
rr.addrs = rr.addrs[:len(rr.addrs)-1]
break
}
}
default:
grpclog.Errorln("Unknown update.Op ", update.Op)
}
}
// Make a copy of rr.addrs and write it onto rr.addrCh so that gRPC internals gets notified.
open := make([]Address, len(rr.addrs))
for i, v := range rr.addrs {
open[i] = v.addr
}
if rr.done {
return ErrClientConnClosing
}
select {
case <-rr.addrCh:
default:
}
rr.addrCh <- open
return nil
}
func (rr *roundRobin) Start(target string, config BalancerConfig) error {
rr.mu.Lock()
defer rr.mu.Unlock()
if rr.done {
return ErrClientConnClosing
}
if rr.r == nil {
// If there is no name resolver installed, it is not needed to
// do name resolution. In this case, target is added into rr.addrs
// as the only address available and rr.addrCh stays nil.
rr.addrs = append(rr.addrs, &addrInfo{addr: Address{Addr: target}})
return nil
}
w, err := rr.r.Resolve(target)
if err != nil {
return err
}
rr.w = w
rr.addrCh = make(chan []Address, 1)
go func() {
for {
if err := rr.watchAddrUpdates(); err != nil {
return
}
}
}()
return nil
}
// Up sets the connected state of addr and sends notification if there are pending
// Get() calls.
func (rr *roundRobin) Up(addr Address) func(error) {
rr.mu.Lock()
defer rr.mu.Unlock()
var cnt int
for _, a := range rr.addrs {
if a.addr == addr {
if a.connected {
return nil
}
a.connected = true
}
if a.connected {
cnt++
}
}
// addr is only one which is connected. Notify the Get() callers who are blocking.
if cnt == 1 && rr.waitCh != nil {
close(rr.waitCh)
rr.waitCh = nil
}
return func(err error) {
rr.down(addr, err)
}
}
// down unsets the connected state of addr.
func (rr *roundRobin) down(addr Address, err error) {
rr.mu.Lock()
defer rr.mu.Unlock()
for _, a := range rr.addrs {
if addr == a.addr {
a.connected = false
break
}
}
}
// Get returns the next addr in the rotation.
func (rr *roundRobin) Get(ctx context.Context, opts BalancerGetOptions) (addr Address, put func(), err error) {
var ch chan struct{}
rr.mu.Lock()
if rr.done {
rr.mu.Unlock()
err = ErrClientConnClosing
return
}
if len(rr.addrs) > 0 {
if rr.next >= len(rr.addrs) {
rr.next = 0
}
next := rr.next
for {
a := rr.addrs[next]
next = (next + 1) % len(rr.addrs)
if a.connected {
addr = a.addr
rr.next = next
rr.mu.Unlock()
return
}
if next == rr.next {
// Has iterated all the possible address but none is connected.
break
}
}
}
if !opts.BlockingWait {
if len(rr.addrs) == 0 {
rr.mu.Unlock()
err = status.Errorf(codes.Unavailable, "there is no address available")
return
}
// Returns the next addr on rr.addrs for failfast RPCs.
addr = rr.addrs[rr.next].addr
rr.next++
rr.mu.Unlock()
return
}
// Wait on rr.waitCh for non-failfast RPCs.
if rr.waitCh == nil {
ch = make(chan struct{})
rr.waitCh = ch
} else {
ch = rr.waitCh
}
rr.mu.Unlock()
for {
select {
case <-ctx.Done():
err = ctx.Err()
return
case <-ch:
rr.mu.Lock()
if rr.done {
rr.mu.Unlock()
err = ErrClientConnClosing
return
}
if len(rr.addrs) > 0 {
if rr.next >= len(rr.addrs) {
rr.next = 0
}
next := rr.next
for {
a := rr.addrs[next]
next = (next + 1) % len(rr.addrs)
if a.connected {
addr = a.addr
rr.next = next
rr.mu.Unlock()
return
}
if next == rr.next {
// Has iterated all the possible address but none is connected.
break
}
}
}
// The newly added addr got removed by Down() again.
if rr.waitCh == nil {
ch = make(chan struct{})
rr.waitCh = ch
} else {
ch = rr.waitCh
}
rr.mu.Unlock()
}
}
}
func (rr *roundRobin) Notify() <-chan []Address {
return rr.addrCh
}
func (rr *roundRobin) Close() error {
rr.mu.Lock()
defer rr.mu.Unlock()
if rr.done {
return errBalancerClosed
}
rr.done = true
if rr.w != nil {
rr.w.Close()
}
if rr.waitCh != nil {
close(rr.waitCh)
rr.waitCh = nil
}
if rr.addrCh != nil {
close(rr.addrCh)
}
return nil
}
// pickFirst is used to test multi-addresses in one addrConn in which all addresses share the same addrConn.
// It is a wrapper around roundRobin balancer. The logic of all methods works fine because balancer.Get()
// returns the only address Up by resetTransport().
type pickFirst struct {
*roundRobin
}