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eds_impl_priority.go
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eds_impl_priority.go
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/*
*
* Copyright 2019 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 edsbalancer
import (
"errors"
"fmt"
"time"
"google.golang.org/grpc/balancer"
"google.golang.org/grpc/balancer/base"
"google.golang.org/grpc/connectivity"
)
var errAllPrioritiesRemoved = errors.New("eds: no locality is provided, all priorities are removed")
// handlePriorityChange handles priority after EDS adds/removes a
// priority.
//
// - If all priorities were deleted, unset priorityInUse, and set parent
// ClientConn to TransientFailure
// - If priorityInUse wasn't set, this is either the first EDS resp, or the
// previous EDS resp deleted everything. Set priorityInUse to 0, and start 0.
// - If priorityInUse was deleted, send the picker from the new lowest priority
// to parent ClientConn, and set priorityInUse to the new lowest.
// - If priorityInUse has a non-Ready state, and also there's a priority lower
// than priorityInUse (which means a lower priority was added), set the next
// priority as new priorityInUse, and start the bg.
func (edsImpl *edsBalancerImpl) handlePriorityChange() {
edsImpl.priorityMu.Lock()
defer edsImpl.priorityMu.Unlock()
// Everything was removed by EDS.
if !edsImpl.priorityLowest.isSet() {
edsImpl.priorityInUse = newPriorityTypeUnset()
// Stop the init timer. This can happen if the only priority is removed
// shortly after it's added.
if timer := edsImpl.priorityInitTimer; timer != nil {
timer.Stop()
edsImpl.priorityInitTimer = nil
}
edsImpl.cc.UpdateState(balancer.State{ConnectivityState: connectivity.TransientFailure, Picker: base.NewErrPicker(errAllPrioritiesRemoved)})
return
}
// priorityInUse wasn't set, use 0.
if !edsImpl.priorityInUse.isSet() {
edsImpl.logger.Infof("Switching priority from unset to %v", 0)
edsImpl.startPriority(newPriorityType(0))
return
}
// priorityInUse was deleted, use the new lowest.
if _, ok := edsImpl.priorityToLocalities[edsImpl.priorityInUse]; !ok {
oldP := edsImpl.priorityInUse
edsImpl.priorityInUse = edsImpl.priorityLowest
edsImpl.logger.Infof("Switching priority from %v to %v, because former was deleted", oldP, edsImpl.priorityInUse)
if s, ok := edsImpl.priorityToState[edsImpl.priorityLowest]; ok {
edsImpl.cc.UpdateState(*s)
} else {
// If state for priorityLowest is not found, this means priorityLowest was
// started, but never sent any update. The init timer fired and
// triggered the next priority. The old_priorityInUse (that was just
// deleted EDS) was picked later.
//
// We don't have an old state to send to parent, but we also don't
// want parent to keep using picker from old_priorityInUse. Send an
// update to trigger block picks until a new picker is ready.
edsImpl.cc.UpdateState(balancer.State{ConnectivityState: connectivity.Connecting, Picker: base.NewErrPicker(balancer.ErrNoSubConnAvailable)})
}
return
}
// priorityInUse is not ready, look for next priority, and use if found.
if s, ok := edsImpl.priorityToState[edsImpl.priorityInUse]; ok && s.ConnectivityState != connectivity.Ready {
pNext := edsImpl.priorityInUse.nextLower()
if _, ok := edsImpl.priorityToLocalities[pNext]; ok {
edsImpl.logger.Infof("Switching priority from %v to %v, because latter was added, and former wasn't Ready")
edsImpl.startPriority(pNext)
}
}
}
// startPriority sets priorityInUse to p, and starts the balancer group for p.
// It also starts a timer to fall to next priority after timeout.
//
// Caller must hold priorityMu, priority must exist, and edsImpl.priorityInUse
// must be non-nil.
func (edsImpl *edsBalancerImpl) startPriority(priority priorityType) {
edsImpl.priorityInUse = priority
p := edsImpl.priorityToLocalities[priority]
// NOTE: this will eventually send addresses to sub-balancers. If the
// sub-balancer tries to update picker, it will result in a deadlock on
// priorityMu in the update is handled synchronously. The deadlock is
// currently avoided by handling balancer update in a goroutine (the run
// goroutine in the parent eds balancer). When priority balancer is split
// into its own, this asynchronous state handling needs to be copied.
p.stateAggregator.Start()
p.bg.Start()
// startPriority can be called when
// 1. first EDS resp, start p0
// 2. a high priority goes Failure, start next
// 3. a high priority init timeout, start next
//
// In all the cases, the existing init timer is either closed, also already
// expired. There's no need to close the old timer.
edsImpl.priorityInitTimer = time.AfterFunc(defaultPriorityInitTimeout, func() {
edsImpl.priorityMu.Lock()
defer edsImpl.priorityMu.Unlock()
if !edsImpl.priorityInUse.isSet() || !edsImpl.priorityInUse.equal(priority) {
return
}
edsImpl.priorityInitTimer = nil
pNext := priority.nextLower()
if _, ok := edsImpl.priorityToLocalities[pNext]; ok {
edsImpl.startPriority(pNext)
}
})
}
// handlePriorityWithNewState start/close priorities based on the connectivity
// state. It returns whether the state should be forwarded to parent ClientConn.
func (edsImpl *edsBalancerImpl) handlePriorityWithNewState(priority priorityType, s balancer.State) bool {
edsImpl.priorityMu.Lock()
defer edsImpl.priorityMu.Unlock()
if !edsImpl.priorityInUse.isSet() {
edsImpl.logger.Infof("eds: received picker update when no priority is in use (EDS returned an empty list)")
return false
}
if edsImpl.priorityInUse.higherThan(priority) {
// Lower priorities should all be closed, this is an unexpected update.
edsImpl.logger.Infof("eds: received picker update from priority lower then priorityInUse")
return false
}
bState, ok := edsImpl.priorityToState[priority]
if !ok {
bState = &balancer.State{}
edsImpl.priorityToState[priority] = bState
}
oldState := bState.ConnectivityState
*bState = s
switch s.ConnectivityState {
case connectivity.Ready:
return edsImpl.handlePriorityWithNewStateReady(priority)
case connectivity.TransientFailure:
return edsImpl.handlePriorityWithNewStateTransientFailure(priority)
case connectivity.Connecting:
return edsImpl.handlePriorityWithNewStateConnecting(priority, oldState)
default:
// New state is Idle, should never happen. Don't forward.
return false
}
}
// handlePriorityWithNewStateReady handles state Ready and decides whether to
// forward update or not.
//
// An update with state Ready:
// - If it's from higher priority:
// - Forward the update
// - Set the priority as priorityInUse
// - Close all priorities lower than this one
// - If it's from priorityInUse:
// - Forward and do nothing else
//
// Caller must make sure priorityInUse is not higher than priority.
//
// Caller must hold priorityMu.
func (edsImpl *edsBalancerImpl) handlePriorityWithNewStateReady(priority priorityType) bool {
// If one priority higher or equal to priorityInUse goes Ready, stop the
// init timer. If update is from higher than priorityInUse,
// priorityInUse will be closed, and the init timer will become useless.
if timer := edsImpl.priorityInitTimer; timer != nil {
timer.Stop()
edsImpl.priorityInitTimer = nil
}
if edsImpl.priorityInUse.lowerThan(priority) {
edsImpl.logger.Infof("Switching priority from %v to %v, because latter became Ready", edsImpl.priorityInUse, priority)
edsImpl.priorityInUse = priority
for i := priority.nextLower(); !i.lowerThan(edsImpl.priorityLowest); i = i.nextLower() {
bgwc := edsImpl.priorityToLocalities[i]
bgwc.stateAggregator.Stop()
bgwc.bg.Close()
}
return true
}
return true
}
// handlePriorityWithNewStateTransientFailure handles state TransientFailure and
// decides whether to forward update or not.
//
// An update with state Failure:
// - If it's from a higher priority:
// - Do not forward, and do nothing
// - If it's from priorityInUse:
// - If there's no lower:
// - Forward and do nothing else
// - If there's a lower priority:
// - Forward
// - Set lower as priorityInUse
// - Start lower
//
// Caller must make sure priorityInUse is not higher than priority.
//
// Caller must hold priorityMu.
func (edsImpl *edsBalancerImpl) handlePriorityWithNewStateTransientFailure(priority priorityType) bool {
if edsImpl.priorityInUse.lowerThan(priority) {
return false
}
// priorityInUse sends a failure. Stop its init timer.
if timer := edsImpl.priorityInitTimer; timer != nil {
timer.Stop()
edsImpl.priorityInitTimer = nil
}
pNext := priority.nextLower()
if _, okNext := edsImpl.priorityToLocalities[pNext]; !okNext {
return true
}
edsImpl.logger.Infof("Switching priority from %v to %v, because former became TransientFailure", priority, pNext)
edsImpl.startPriority(pNext)
return true
}
// handlePriorityWithNewStateConnecting handles state Connecting and decides
// whether to forward update or not.
//
// An update with state Connecting:
// - If it's from a higher priority
// - Do nothing
// - If it's from priorityInUse, the behavior depends on previous state.
//
// When new state is Connecting, the behavior depends on previous state. If the
// previous state was Ready, this is a transition out from Ready to Connecting.
// Assuming there are multiple backends in the same priority, this mean we are
// in a bad situation and we should failover to the next priority (Side note:
// the current connectivity state aggregating algorhtim (e.g. round-robin) is
// not handling this right, because if many backends all go from Ready to
// Connecting, the overall situation is more like TransientFailure, not
// Connecting).
//
// If the previous state was Idle, we don't do anything special with failure,
// and simply forward the update. The init timer should be in process, will
// handle failover if it timeouts. If the previous state was TransientFailure,
// we do not forward, because the lower priority is in use.
//
// Caller must make sure priorityInUse is not higher than priority.
//
// Caller must hold priorityMu.
func (edsImpl *edsBalancerImpl) handlePriorityWithNewStateConnecting(priority priorityType, oldState connectivity.State) bool {
if edsImpl.priorityInUse.lowerThan(priority) {
return false
}
switch oldState {
case connectivity.Ready:
pNext := priority.nextLower()
if _, okNext := edsImpl.priorityToLocalities[pNext]; !okNext {
return true
}
edsImpl.logger.Infof("Switching priority from %v to %v, because former became Connecting from Ready", priority, pNext)
edsImpl.startPriority(pNext)
return true
case connectivity.Idle:
return true
case connectivity.TransientFailure:
return false
default:
// Old state is Connecting or Shutdown. Don't forward.
return false
}
}
// priorityType represents the priority from EDS response.
//
// 0 is the highest priority. The bigger the number, the lower the priority.
type priorityType struct {
set bool
p uint32
}
func newPriorityType(p uint32) priorityType {
return priorityType{
set: true,
p: p,
}
}
func newPriorityTypeUnset() priorityType {
return priorityType{}
}
func (p priorityType) isSet() bool {
return p.set
}
func (p priorityType) equal(p2 priorityType) bool {
if !p.isSet() && !p2.isSet() {
return true
}
if !p.isSet() || !p2.isSet() {
return false
}
return p == p2
}
func (p priorityType) higherThan(p2 priorityType) bool {
if !p.isSet() || !p2.isSet() {
// TODO(menghanl): return an appropriate value instead of panic.
panic("priority unset")
}
return p.p < p2.p
}
func (p priorityType) lowerThan(p2 priorityType) bool {
if !p.isSet() || !p2.isSet() {
// TODO(menghanl): return an appropriate value instead of panic.
panic("priority unset")
}
return p.p > p2.p
}
func (p priorityType) nextLower() priorityType {
if !p.isSet() {
panic("priority unset")
}
return priorityType{
set: true,
p: p.p + 1,
}
}
func (p priorityType) String() string {
if !p.set {
return "Nil"
}
return fmt.Sprint(p.p)
}