working on a g-counter example

g-counter
Jordan Orelli 4 years ago
parent e43149ab98
commit 51c22cfb94

@ -0,0 +1,47 @@
package main
import (
"encoding/json"
"sort"
)
type gcounter struct {
id int
counts map[int]int
}
func (c gcounter) incr() { c.counts[c.id]++ }
func (c gcounter) total() int {
var n int
for _, count := range c.counts {
n += count
}
return n
}
func (c gcounter) merge(other gcounter) {
for id, count := range other.counts {
if c.[id] < count {
c.[id] = count
}
}
}
type pair [2]int
func (c gcounter) MarshalJSON() ([]byte, error) {
pairs := make([]pair, 0, len(c.counts))
for id, count := range c.counts {
pairs = append(pairs, pair{id, count})
}
sort.Slice(pairs, func(i, j int) bool { return pairs[i][0] < pairs[j][0] })
return json.Marshal(pairs)
}
func (c *gcounter) UnmarshalJSON(b []byte) error {
pairs := make([]pair, 0, len(c.counts))
if err := json.Unmarshal(b, &pairs); err != nil {
return err
}
}

@ -0,0 +1,71 @@
package main
import (
"encoding/json"
"testing"
)
func TestGCounterJSON(t *testing.T) {
t.Run("marshal", func(t *testing.T) {
type test struct {
counter gcounter
expect string
}
tests := []test{
{
gcounter{1, map[int]int{1: 5, 3: 8}},
`[[1,5],[3,8]]`,
},
{
gcounter{8, map[int]int{3: 10, 7: 16, 12: 9, 2: 37}},
`[[2,37],[3,10],[7,16],[12,9]]`,
},
}
for _, test := range tests {
b, err := json.Marshal(test.counter)
if err != nil {
t.Errorf("marshal failed: %s", err)
continue
}
s := string(b)
if s != test.expect {
t.Errorf("expected json: %s received: %s", test.expect, s)
}
}
})
t.Run("unmarshal", func(t *testing.T) {
type test struct {
in string
expect gcounter
}
tests := []test{
{
`[[1,5],[3,8]]`,
gcounter{1, map[int]int{1: 5, 3: 8}},
},
{
`[[2,37],[3,10],[7,16],[12,9]]`,
gcounter{8, map[int]int{3: 10, 7: 16, 12: 9, 2: 37}},
},
}
for _, test := range tests {
var c gcounter
if err := json.Unmarshal(test.in, &c); err != nil {
t.Errorf("unmarshal failed: %s", err)
continue
}
for id, count := range c.counts {
n := test.expect.counts[id]
if n != count {
t.Errorf("mismatched counts for id %d: expected %d, saw %d", id, count, n)
}
}
}
})
}

@ -0,0 +1,78 @@
package main
import (
"encoding/json"
"fmt"
"net/http"
"sync"
)
type response struct {
OK bool `json:"ok"`
Hits int `json:"hits"`
}
// server implements a clustered http hit-counter server. Each path is given a
// g-counter, and every node in the cluster acts as a read-write replica.
type server struct {
sync.Mutex
// my own id
id int
// a mapping of peer servers id -> addr
peers map[int]string
// distributed counts
counters map[string]gcounter
}
func (s *server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
switch r.URL.Path {
case "/join":
s.join(w, r)
case "/sync":
s.sync(w, r)
default:
s.countHit(w, r)
}
}
func (s *server) countHit(w http.ResponseWriter, r *http.Request) {
hits := s.hit(r.URL.Path)
fmt.Printf("% 8d %s\n", hits, r.URL.Path)
w.Header().Add("Content-Type", "application/json")
json.NewEncoder(w).Encode(response{OK: true, Hits: hits})
}
func (s *server) join(w http.ResponseWriter, r *http.Request) {
var body struct {
Addr string `json:"addr"`
}
}
func (s *server) sync(w http.ResponseWriter, r *http.Request) {
}
func (s *server) hit(path string) int {
s.Lock()
defer s.Unlock()
if s.counters == nil {
s.counters = map[string]gcounter{
gcounter{s.id, map[int]int{id: 1}},
}
return 1
}
c, ok := s.counters[path]
if !ok {
s.counters[path] = gcounter{s.id, map[int]int{id: 1}}
return 1
}
c.incr()
return c.total()
}

@ -59,7 +59,7 @@ func TestServer(t *testing.T) {
return node return node
} }
runParallel := func(node *tea.Tree, tests list) { runSiblings := func(node *tea.Tree, tests list) {
for i := 0; i < len(tests); i++ { for i := 0; i < len(tests); i++ {
node.Child(&tests[i]) node.Child(&tests[i])
} }
@ -82,7 +82,7 @@ func TestServer(t *testing.T) {
{path: "/users/bob", expect: 2}, {path: "/users/bob", expect: 2},
}) })
runParallel(root, list{ runSiblings(root, list{
{path: "/users/alice", expect: 1}, {path: "/users/alice", expect: 1},
{path: "/users/alice", expect: 1}, {path: "/users/alice", expect: 1},
{path: "/users/alice", expect: 1}, {path: "/users/alice", expect: 1},

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