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routing.go
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routing.go
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// Copyright 2022 Google LLC
//
// 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 weaver
import (
"context"
"crypto/tls"
"math/rand"
"sync"
"github.com/ServiceWeaver/weaver/internal/cond"
"github.com/ServiceWeaver/weaver/internal/net/call"
"github.com/ServiceWeaver/weaver/runtime/protos"
"github.com/google/uuid"
)
// routingBalancer balances requests according to a routing assignment.
type routingBalancer struct {
balancer call.Balancer // default balancer
tlsConfig *tls.Config // tls config to use; may be nil.
mu sync.RWMutex
assignment *protos.Assignment
index index
}
// newRoutingBalancer returns a new routingBalancer.
func newRoutingBalancer(tlsConfig *tls.Config) *routingBalancer {
return &routingBalancer{balancer: call.RoundRobin(), tlsConfig: tlsConfig}
}
// Update implements the call.Balancer interface.
func (rb *routingBalancer) Update(endpoints []call.Endpoint) {
rb.balancer.Update(endpoints)
}
// update updates the balancer with the provided assignment
func (rb *routingBalancer) update(assignment *protos.Assignment) {
if assignment == nil {
return
}
index := newIndex(assignment)
rb.mu.Lock()
defer rb.mu.Unlock()
rb.assignment = assignment
rb.index = index
}
// Pick implements the call.Balancer interface.
func (rb *routingBalancer) Pick(opts call.CallOptions) (call.Endpoint, error) {
if opts.ShardKey == 0 {
// If the method we're calling is not sharded (which is guaranteed to
// be true for nonsharded components), then the shard key is 0.
return rb.balancer.Pick(opts)
}
// Grab the current assignment. It's possible that the current assignment
// changes between when we release the lock and when we pick an endpoint,
// but using a slightly stale assignment is okay.
rb.mu.RLock()
assignment := rb.assignment
index := rb.index
rb.mu.RUnlock()
if assignment == nil {
// There is no assignment. This is possible if we haven't received an
// assignment from the assigner yet.
return rb.balancer.Pick(opts)
}
slice, ok := index.find(opts.ShardKey)
if !ok {
// TODO(mwhittaker): Shouldn't this be impossible. Understand better
// when this happens.
return rb.balancer.Pick(opts)
}
// TODO(mwhittaker): Double check that the endpoint in the slice is one of
// the endpoints in rb.endpoints.
//
// TODO(mwhittaker): Parse the endpoints when an assignment is received,
// rather than once per call.
addr := slice.replicas[rand.Intn(len(slice.replicas))]
endpoints, err := parseEndpoints([]string{addr}, rb.tlsConfig)
if err != nil {
return nil, err
}
return endpoints[0], nil
}
// routingResolver is a dummy resolver that returns whatever endpoints are
// passed to the update method.
type routingResolver struct {
m sync.Mutex // guards all of the following fields
changed cond.Cond // fires when endpoints changes
version *call.Version // the current version of endpoints
endpoints []call.Endpoint // the endpoints returned by Resolve
}
// newRoutingResolver returns a new routingResolver.
func newRoutingResolver() *routingResolver {
r := &routingResolver{
version: &call.Version{Opaque: call.Missing.Opaque},
}
r.changed.L = &r.m
return r
}
// IsConstant implements the call.Resolver interface.
func (rr *routingResolver) IsConstant() bool { return false }
// update updates the resolver with the provided endpoints.
func (rr *routingResolver) update(endpoints []call.Endpoint) {
rr.m.Lock()
defer rr.m.Unlock()
rr.version = &call.Version{Opaque: uuid.New().String()}
rr.endpoints = endpoints
rr.changed.Broadcast()
}
// Resolve implements the call.Resolver interface.
func (rr *routingResolver) Resolve(ctx context.Context, version *call.Version) ([]call.Endpoint, *call.Version, error) {
rr.m.Lock()
defer rr.m.Unlock()
if version == nil {
return rr.endpoints, rr.version, nil
}
for *version == *rr.version {
if err := rr.changed.Wait(ctx); err != nil {
return nil, nil, err
}
}
return rr.endpoints, rr.version, nil
}