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infostore.go
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infostore.go
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// Copyright 2014 The Cockroach 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. See the AUTHORS file
// for names of contributors.
//
// Author: Spencer Kimball (spencer.kimball@gmail.com)
package gossip
import (
"bytes"
"fmt"
"math"
"regexp"
"sync"
"time"
"github.com/cockroachdb/cockroach/proto"
"github.com/cockroachdb/cockroach/util"
"github.com/cockroachdb/cockroach/util/log"
)
// callback holds regexp pattern match and GossipCallback method.
type callback struct {
pattern *regexp.Regexp
method Callback
}
// infoStore objects manage maps of Info objects. They maintain a
// sequence number generator which they use to allocate new info
// objects.
//
// infoStores can be queried for incremental updates occurring since a
// specified sequence number.
//
// infoStores can be combined using deltas from peer nodes.
//
// infoStores are not thread safe.
type infoStore struct {
Infos infoMap `json:"infos,omitempty"` // Map from key to info
NodeID proto.NodeID `json:"-"` // Owning node's ID
NodeAddr util.UnresolvedAddr `json:"-"` // Address of node owning this info store: "host:port"
MaxSeq int64 `json:"-"` // Maximum sequence number inserted
seqGen int64 // Sequence generator incremented each time info is added
callbacks []callback
}
// monotonicUnixNano returns a monotonically increasing value for
// nanoseconds in Unix time. Since equal times are ignored with
// updates to infos, we're careful to avoid incorrectly ignoring a
// newly created value in the event one is created within the same
// nanosecond. Really unlikely except for the case of unittests, but
// better safe than sorry.
func monotonicUnixNano() int64 {
monoTimeMu.Lock()
defer monoTimeMu.Unlock()
now := time.Now().UnixNano()
if now <= lastTime {
now = lastTime + 1
}
lastTime = now
return now
}
// String returns a string representation of an infostore.
func (is *infoStore) String() string {
buf := bytes.Buffer{}
if infoCount := len(is.Infos); infoCount > 0 {
fmt.Fprintf(&buf, "infostore with %d info(s): ", infoCount)
} else {
return "infostore (empty)"
}
prepend := ""
if err := is.visitInfos(func(key string, i *info) error {
fmt.Fprintf(&buf, "%sinfo %q: %+v", prepend, key, i.Value)
prepend = ", "
return nil
}); err != nil {
log.Errorf("failed to properly construct string representation of infoStore: %s", err)
}
return buf.String()
}
var (
monoTimeMu sync.Mutex
lastTime int64
)
// newInfoStore allocates and returns a new infoStore.
func newInfoStore(nodeID proto.NodeID, nodeAddr util.UnresolvedAddr) infoStore {
return infoStore{
Infos: make(infoMap),
NodeID: nodeID,
NodeAddr: nodeAddr,
}
}
// newInfo allocates and returns a new info object using specified key,
// value, and time-to-live.
func (is *infoStore) newInfo(val []byte, ttl time.Duration) *info {
is.seqGen++
now := monotonicUnixNano()
ttlStamp := now + int64(ttl)
if ttl == 0 {
ttlStamp = math.MaxInt64
}
return &info{
Info: Info{
Value: proto.Value{
Bytes: val,
Timestamp: &proto.Timestamp{
WallTime: now,
},
},
TTLStamp: ttlStamp,
NodeID: is.NodeID,
},
peerID: is.NodeID,
seq: is.seqGen,
}
}
// getInfo returns the Info at key. Returns nil when key is not present
// in the infoStore.
func (is *infoStore) getInfo(key string) *info {
if info, ok := is.Infos[key]; ok {
// Check TTL and discard if too old.
if info.expired(time.Now().UnixNano()) {
delete(is.Infos, key)
} else {
return info
}
}
return nil
}
// addInfo adds or updates an info in the infos map.
//
// Returns nil if info was added; error otherwise.
func (is *infoStore) addInfo(key string, i *info) error {
// Only replace an existing info if new timestamp is greater, or if
// timestamps are equal, but new hops is smaller.
if existingInfo, ok := is.Infos[key]; ok {
iNanos := i.Value.Timestamp.WallTime
existingNanos := existingInfo.Value.Timestamp.WallTime
if iNanos < existingNanos || (iNanos == existingNanos && i.Hops >= existingInfo.Hops) {
return util.Errorf("info %+v older than current info %+v", i, existingInfo)
}
}
i.Value.InitChecksum([]byte(key))
// Update info map.
is.Infos[key] = i
if i.seq > is.MaxSeq {
is.MaxSeq = i.seq
}
is.processCallbacks(key, i.Value.Bytes)
return nil
}
// maxHops returns the maximum hops across all infos in the store.
// This is the maximum number of gossip exchanges between any
// originator and this node.
func (is *infoStore) maxHops() uint32 {
var maxHops uint32
if err := is.visitInfos(func(key string, i *info) error {
if i.Hops > maxHops {
maxHops = i.Hops
}
return nil
}); err != nil {
panic(err)
}
return maxHops
}
// registerCallback compiles a regexp for pattern and adds it to
// the callbacks slice.
func (is *infoStore) registerCallback(pattern string, method Callback) {
re := regexp.MustCompile(pattern)
is.callbacks = append(is.callbacks, callback{pattern: re, method: method})
infos := make(infoMap)
if err := is.visitInfos(func(key string, i *info) error {
if re.MatchString(key) {
infos[key] = i
}
return nil
}); err != nil {
panic(err)
}
// Run callbacks in a goroutine to avoid mutex reentry.
go func() {
for key, i := range infos {
method(key, i.Value.Bytes)
}
}()
}
// processCallbacks processes callbacks for the specified key by
// matching callback regular expression against the key and invoking
// the corresponding callback method on a match.
func (is *infoStore) processCallbacks(key string, content []byte) {
var matches []callback
for _, cb := range is.callbacks {
if cb.pattern.MatchString(key) {
matches = append(matches, cb)
}
}
// Run callbacks in a goroutine to avoid mutex reentry.
go func() {
for _, cb := range matches {
cb.method(key, content)
}
}()
}
// visitInfos implements a visitor pattern to run the visitInfo
// function against each info in turn. Be sure to skip over any expired
// infos.
func (is *infoStore) visitInfos(visitInfo func(string, *info) error) error {
now := time.Now().UnixNano()
if visitInfo != nil {
for k, i := range is.Infos {
if i.expired(now) {
delete(is.Infos, k)
continue
}
if err := visitInfo(k, i); err != nil {
return err
}
}
}
return nil
}
// combine combines an incremental delta with the current infoStore.
// The sequence numbers on all info objects are reset using the info
// store's sequence generator. All hop distances on infos are
// incremented to indicate they've arrived from an external source.
// Returns the count of "fresh" infos in the provided delta.
func (is *infoStore) combine(infos map[string]*Info, nodeID proto.NodeID) int {
var freshCount int
for key, infoProto := range infos {
i := &info{
Info: *infoProto,
}
is.seqGen++
i.seq = is.seqGen
i.Hops++
i.peerID = nodeID
// Errors from addInfo here are not a problem; they simply
// indicate that the data in *is is newer than in *delta.
if err := is.addInfo(key, i); err == nil {
freshCount++
}
}
return freshCount
}
// delta returns an incremental delta of infos added to the info store
// since (not including) the specified sequence number. These deltas
// are intended for efficiently updating peer nodes. Any infos passed
// from node requesting delta are ignored.
//
// Returns nil if there are no deltas.
func (is *infoStore) delta(nodeID proto.NodeID, seq int64) map[string]*Info {
infos := make(map[string]*Info)
if seq < is.MaxSeq {
// Compute delta of infos.
if err := is.visitInfos(func(key string, i *info) error {
if i.isFresh(nodeID, seq) {
infos[key] = &i.Info
}
return nil
}); err != nil {
panic(err)
}
}
return infos
}
// distant returns a nodeSet for gossip peers which originated infos
// with info.Hops > maxHops.
func (is *infoStore) distant(maxHops uint32) nodeSet {
ns := makeNodeSet(0)
if err := is.visitInfos(func(key string, i *info) error {
if i.Hops > maxHops {
ns.addNode(i.NodeID)
}
return nil
}); err != nil {
panic(err)
}
return ns
}
// leastUseful determines which node ID from amongst the set is
// currently contributing the least. Returns 0 if nodes is empty.
func (is *infoStore) leastUseful(nodes nodeSet) proto.NodeID {
contrib := make(map[proto.NodeID]int, nodes.len())
for node := range nodes.nodes {
contrib[node] = 0
}
if err := is.visitInfos(func(key string, i *info) error {
contrib[i.peerID]++
return nil
}); err != nil {
panic(err)
}
least := math.MaxInt32
var leastNode proto.NodeID
for id, count := range contrib {
if nodes.hasNode(id) {
if count < least {
least = count
leastNode = id
}
}
}
return leastNode
}