vendor/google.golang.org/api/internal/pool.go

   1 // Copyright 2016 Google LLC
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //      http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 package internal
  16
  17 import (
  18         "errors"
  19
  20         "google.golang.org/grpc/naming"
  21 )
  22
  23 // PoolResolver provides a fixed list of addresses to load balance between
  24 // and does not provide further updates.
  25 type PoolResolver struct {
  26         poolSize int
  27         dialOpt  *DialSettings
  28         ch       chan []*naming.Update
  29 }
  30
  31 // NewPoolResolver returns a PoolResolver
  32 // This is an EXPERIMENTAL API and may be changed or removed in the future.
  33 func NewPoolResolver(size int, o *DialSettings) *PoolResolver {
  34         return &PoolResolver{poolSize: size, dialOpt: o}
  35 }
  36
  37 // Resolve returns a Watcher for the endpoint defined by the DialSettings
  38 // provided to NewPoolResolver.
  39 func (r *PoolResolver) Resolve(target string) (naming.Watcher, error) {
  40         if r.dialOpt.Endpoint == "" {
  41                 return nil, errors.New("No endpoint configured")
  42         }
  43         addrs := make([]*naming.Update, 0, r.poolSize)
  44         for i := 0; i < r.poolSize; i++ {
  45                 addrs = append(addrs, &naming.Update{Op: naming.Add, Addr: r.dialOpt.Endpoint, Metadata: i})
  46         }
  47         r.ch = make(chan []*naming.Update, 1)
  48         r.ch <- addrs
  49         return r, nil
  50 }
  51
  52 // Next returns a static list of updates on the first call,
  53 // and blocks indefinitely until Close is called on subsequent calls.
  54 func (r *PoolResolver) Next() ([]*naming.Update, error) {
  55         return <-r.ch, nil
  56 }
  57
  58 // Close releases resources associated with the pool and causes Next to unblock.
  59 func (r *PoolResolver) Close() {
  60         close(r.ch)
  61 }