tusd/vendor/google.golang.org/grpc/balancer/roundrobin/roundrobin.go

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2017-11-20 21:35:32 +00:00
/*
*
* Copyright 2017 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 roundrobin defines a roundrobin balancer. Roundrobin balancer is
// installed as one of the default balancers in gRPC, users don't need to
// explicitly install this balancer.
package roundrobin
import (
"sync"
"golang.org/x/net/context"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/connectivity"
"google.golang.org/grpc/grpclog"
"google.golang.org/grpc/resolver"
)
// newBuilder creates a new roundrobin balancer builder.
func newBuilder() balancer.Builder {
return &rrBuilder{}
}
func init() {
balancer.Register(newBuilder())
}
type rrBuilder struct{}
func (*rrBuilder) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
return &rrBalancer{
cc: cc,
subConns: make(map[resolver.Address]balancer.SubConn),
scStates: make(map[balancer.SubConn]connectivity.State),
csEvltr: &connectivityStateEvaluator{},
// Initialize picker to a picker that always return
// ErrNoSubConnAvailable, because when state of a SubConn changes, we
// may call UpdateBalancerState with this picker.
picker: newPicker([]balancer.SubConn{}, nil),
}
}
func (*rrBuilder) Name() string {
return "round_robin"
}
type rrBalancer struct {
cc balancer.ClientConn
csEvltr *connectivityStateEvaluator
state connectivity.State
subConns map[resolver.Address]balancer.SubConn
scStates map[balancer.SubConn]connectivity.State
picker *picker
}
func (b *rrBalancer) HandleResolvedAddrs(addrs []resolver.Address, err error) {
if err != nil {
grpclog.Infof("roundrobin.rrBalancer: HandleResolvedAddrs called with error %v", err)
return
}
grpclog.Infoln("roundrobin.rrBalancer: got new resolved addresses: ", addrs)
// addrsSet is the set converted from addrs, it's used for quick lookup of an address.
addrsSet := make(map[resolver.Address]struct{})
for _, a := range addrs {
addrsSet[a] = struct{}{}
if _, ok := b.subConns[a]; !ok {
// a is a new address (not existing in b.subConns).
sc, err := b.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{})
if err != nil {
grpclog.Warningf("roundrobin.rrBalancer: failed to create new SubConn: %v", err)
continue
}
b.subConns[a] = sc
b.scStates[sc] = connectivity.Idle
sc.Connect()
}
}
for a, sc := range b.subConns {
// a was removed by resolver.
if _, ok := addrsSet[a]; !ok {
b.cc.RemoveSubConn(sc)
delete(b.subConns, a)
// Keep the state of this sc in b.scStates until sc's state becomes Shutdown.
// The entry will be deleted in HandleSubConnStateChange.
}
}
}
// regeneratePicker takes a snapshot of the balancer, and generates a picker
// from it. The picker
// - always returns ErrTransientFailure if the balancer is in TransientFailure,
// - or does round robin selection of all READY SubConns otherwise.
func (b *rrBalancer) regeneratePicker() {
if b.state == connectivity.TransientFailure {
b.picker = newPicker(nil, balancer.ErrTransientFailure)
return
}
var readySCs []balancer.SubConn
for sc, st := range b.scStates {
if st == connectivity.Ready {
readySCs = append(readySCs, sc)
}
}
b.picker = newPicker(readySCs, nil)
}
func (b *rrBalancer) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
grpclog.Infof("roundrobin.rrBalancer: handle SubConn state change: %p, %v", sc, s)
oldS, ok := b.scStates[sc]
if !ok {
grpclog.Infof("roundrobin.rrBalancer: got state changes for an unknown SubConn: %p, %v", sc, s)
return
}
b.scStates[sc] = s
switch s {
case connectivity.Idle:
sc.Connect()
case connectivity.Shutdown:
// When an address was removed by resolver, b called RemoveSubConn but
// kept the sc's state in scStates. Remove state for this sc here.
delete(b.scStates, sc)
}
oldAggrState := b.state
b.state = b.csEvltr.recordTransition(oldS, s)
// Regenerate picker when one of the following happens:
// - this sc became ready from not-ready
// - this sc became not-ready from ready
// - the aggregated state of balancer became TransientFailure from non-TransientFailure
// - the aggregated state of balancer became non-TransientFailure from TransientFailure
if (s == connectivity.Ready) != (oldS == connectivity.Ready) ||
(b.state == connectivity.TransientFailure) != (oldAggrState == connectivity.TransientFailure) {
b.regeneratePicker()
}
b.cc.UpdateBalancerState(b.state, b.picker)
return
}
// Close is a nop because roundrobin balancer doesn't internal state to clean
// up, and it doesn't need to call RemoveSubConn for the SubConns.
func (b *rrBalancer) Close() {
}
type picker struct {
// If err is not nil, Pick always returns this err. It's immutable after
// picker is created.
err error
// subConns is the snapshot of the roundrobin balancer when this picker was
// created. The slice is immutable. Each Get() will do a round robin
// selection from it and return the selected SubConn.
subConns []balancer.SubConn
mu sync.Mutex
next int
}
func newPicker(scs []balancer.SubConn, err error) *picker {
grpclog.Infof("roundrobinPicker: newPicker called with scs: %v, %v", scs, err)
if err != nil {
return &picker{err: err}
}
return &picker{
subConns: scs,
}
}
func (p *picker) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
if p.err != nil {
return nil, nil, p.err
}
if len(p.subConns) <= 0 {
return nil, nil, balancer.ErrNoSubConnAvailable
}
p.mu.Lock()
sc := p.subConns[p.next]
p.next = (p.next + 1) % len(p.subConns)
p.mu.Unlock()
return sc, nil, nil
}
// connectivityStateEvaluator gets updated by addrConns when their
// states transition, based on which it evaluates the state of
// ClientConn.
type connectivityStateEvaluator struct {
numReady uint64 // Number of addrConns in ready state.
numConnecting uint64 // Number of addrConns in connecting state.
numTransientFailure uint64 // Number of addrConns in transientFailure.
}
// recordTransition records state change happening in every subConn and based on
// that it evaluates what aggregated state should be.
// It can only transition between Ready, Connecting and TransientFailure. Other states,
// Idle and Shutdown are transitioned into by ClientConn; in the beginning of the connection
// before any subConn is created ClientConn is in idle state. In the end when ClientConn
// closes it is in Shutdown state.
//
// recordTransition should only be called synchronously from the same goroutine.
func (cse *connectivityStateEvaluator) recordTransition(oldState, newState connectivity.State) connectivity.State {
// Update counters.
for idx, state := range []connectivity.State{oldState, newState} {
updateVal := 2*uint64(idx) - 1 // -1 for oldState and +1 for new.
switch state {
case connectivity.Ready:
cse.numReady += updateVal
case connectivity.Connecting:
cse.numConnecting += updateVal
case connectivity.TransientFailure:
cse.numTransientFailure += updateVal
}
}
// Evaluate.
if cse.numReady > 0 {
return connectivity.Ready
}
if cse.numConnecting > 0 {
return connectivity.Connecting
}
return connectivity.TransientFailure
}