1/* 2Copyright 2012 Google Inc. 3 4Licensed under the Apache License, Version 2.0 (the "License"); 5you may not use this file except in compliance with the License. 6You may obtain a copy of the License at 7 8 http://www.apache.org/licenses/LICENSE-2.0 9 10Unless required by applicable law or agreed to in writing, software 11distributed under the License is distributed on an "AS IS" BASIS, 12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13See the License for the specific language governing permissions and 14limitations under the License. 15*/ 16 17// peers.go defines how processes find and communicate with their peers. 18 19package groupcache 20 21import ( 22 pb "github.com/golang/groupcache/groupcachepb" 23) 24 25// Context is an opaque value passed through calls to the 26// ProtoGetter. It may be nil if your ProtoGetter implementation does 27// not require a context. 28type Context interface{} 29 30// ProtoGetter is the interface that must be implemented by a peer. 31type ProtoGetter interface { 32 Get(context Context, in *pb.GetRequest, out *pb.GetResponse) error 33} 34 35// PeerPicker is the interface that must be implemented to locate 36// the peer that owns a specific key. 37type PeerPicker interface { 38 // PickPeer returns the peer that owns the specific key 39 // and true to indicate that a remote peer was nominated. 40 // It returns nil, false if the key owner is the current peer. 41 PickPeer(key string) (peer ProtoGetter, ok bool) 42} 43 44// NoPeers is an implementation of PeerPicker that never finds a peer. 45type NoPeers struct{} 46 47func (NoPeers) PickPeer(key string) (peer ProtoGetter, ok bool) { return } 48 49var ( 50 portPicker func(groupName string) PeerPicker 51) 52 53// RegisterPeerPicker registers the peer initialization function. 54// It is called once, when the first group is created. 55// Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be 56// called exactly once, but not both. 57func RegisterPeerPicker(fn func() PeerPicker) { 58 if portPicker != nil { 59 panic("RegisterPeerPicker called more than once") 60 } 61 portPicker = func(_ string) PeerPicker { return fn() } 62} 63 64// RegisterPerGroupPeerPicker registers the peer initialization function, 65// which takes the groupName, to be used in choosing a PeerPicker. 66// It is called once, when the first group is created. 67// Either RegisterPeerPicker or RegisterPerGroupPeerPicker should be 68// called exactly once, but not both. 69func RegisterPerGroupPeerPicker(fn func(groupName string) PeerPicker) { 70 if portPicker != nil { 71 panic("RegisterPeerPicker called more than once") 72 } 73 portPicker = fn 74} 75 76func getPeers(groupName string) PeerPicker { 77 if portPicker == nil { 78 return NoPeers{} 79 } 80 pk := portPicker(groupName) 81 if pk == nil { 82 pk = NoPeers{} 83 } 84 return pk 85} 86