Client scatter gathers by rw concern

client/cli.go

@@ -5,14 +5,32 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"strconv"
 	"strings"
 )
 
 func main() {
-	client, err := New(strings.Split(os.Getenv("ADDR"), ",")...)
+	rConcernS, ok := os.LookupEnv("RCONCERN")
+	if !ok {
+		rConcernS = "1"
+	}
+	wConcernS, ok := os.LookupEnv("WCONCERN")
+	if !ok {
+		wConcernS = "1"
+	}
+	rConcern, err := strconv.Atoi(rConcernS)
 	if err != nil {
 		panic(err)
 	}
+	wConcern, err := strconv.Atoi(wConcernS)
+	if err != nil {
+		panic(err)
+	}
+	client, err := New(rConcern, wConcern, strings.Split(os.Getenv("ADDR"), ",")...)
+	if err != nil {
+		panic(err)
+	}
+	log.Printf("client: %v", client)
 	reader := bufio.NewReader(os.Stdin)
 	for {
 		fmt.Print("> ")
@@ -46,7 +64,7 @@ func get(client *Client, line string) {
 	words := strings.Split(line, " ")
 	key := words[1]
 	v, err := client.Get(key)
-	log.Printf("set: %v: %s", err, v)
+	log.Printf("get: %v: %s", err, v)
 }
 
 func set(client *Client, line string) {

client/client.go

@@ -3,6 +3,7 @@ package main
 import (
 	"bytes"
 	"errors"
+	"fmt"
 	"io/ioutil"
 	"log"
 	"net"
@@ -15,6 +16,8 @@ import (
 
 type Client struct {
 	hash     *consistent.Consistent
+	wConcern int
+	rConcern int
 }
 
 type hasher struct{}
@@ -33,7 +36,31 @@ func (na netAddr) Network() string {
 	return "tcp"
 }
 
-func New(addrs ...string) (*Client, error) {
+type result struct {
+	b   []byte
+	err error
+}
+
+func (r result) String() string {
+	return fmt.Sprintf("%v : %v", r.err, r.b)
+}
+
+func New(rConcern, wConcern int, addrs ...string) (*Client, error) {
+	if rConcern > len(addrs)-1 {
+		rConcern = len(addrs) - 1
+	}
+	if wConcern > len(addrs)-1 {
+		wConcern = len(addrs) - 1
+	}
+	if rConcern > wConcern {
+		rConcern = wConcern
+	}
+	if rConcern < 1 {
+		rConcern = 1
+	}
+	if wConcern < 1 {
+		wConcern = 1
+	}
 	cfg := consistent.Config{
 		PartitionCount:    71,
 		ReplicationFactor: 20,
@@ -53,11 +80,54 @@ func New(addrs ...string) (*Client, error) {
 	}
 	return &Client{
 		hash:     hash,
+		wConcern: wConcern,
+		rConcern: rConcern,
 	}, nil
 }
 
+func (c *Client) scatterGather(key string, forEach func(addr string, each chan result), try, need int) ([]byte, error) {
+	final := make(chan result)
+	each := make(chan result)
+	members, err := c.hash.GetClosestN([]byte(key), try)
+	if err != nil {
+		return nil, err
+	}
+	for _, member := range members {
+		go forEach(member.String(), each)
+	}
+	go func() {
+		out := make(map[string]int)
+		done := false
+		for i := 0; i < len(members); i++ {
+			one := <-each
+			if done {
+				continue
+			}
+			if _, ok := out[one.String()]; !ok {
+				out[one.String()] = 0
+			}
+			out[one.String()] += 1
+			if out[one.String()] >= need {
+				final <- one
+				done = true
+			}
+		}
+		if !done {
+			final <- result{err: errors.New("no consensus")}
+		}
+	}()
+	consensus := <-final
+	return consensus.b, consensus.err
+}
+
 func (c *Client) Get(key string) ([]byte, error) {
-	addr := c.hash.LocateKey([]byte(key)).String()
+	return c.scatterGather(key, func(addr string, each chan result) {
+		b, err := c.get(addr, key)
+		each <- result{b: b, err: err}
+	}, c.wConcern, c.rConcern)
+}
+
+func (c *Client) get(addr, key string) ([]byte, error) {
 	log.Printf("GET %s FROM %s", key, addr)
 	resp, err := http.Get(addr + "/" + key)
 	if err != nil {
@@ -74,7 +144,14 @@ func (c *Client) Get(key string) ([]byte, error) {
 }
 
 func (c *Client) Set(key string, value []byte) error {
-	addr := c.hash.LocateKey([]byte(key)).String()
+	_, err := c.scatterGather(key, func(addr string, each chan result) {
+		err := c.set(addr, key, value)
+		each <- result{err: err}
+	}, c.wConcern, c.rConcern)
+	return err
+}
+
+func (c *Client) set(addr, key string, value []byte) error {
 	log.Printf("SET %s FROM %s", key, addr)
 	r, err := http.NewRequest("PUT", addr+"/"+key, bytes.NewBuffer(value))
 	if err != nil {

client/client_test.go

@@ -23,7 +23,7 @@ func TestAll(t *testing.T) {
 		go s.Run()
 	}
 
-	client, err := New(addresses...)
+	client, err := New(1, 1, addresses...)
 	if err != nil {
 		t.Fatalf("cannot make client: %v", err)
 	}