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type KeyValue struct {
Key string
Value string
}
type ByKey []KeyValue
func (a ByKey) Len() int { return len(a) }
func (a ByKey) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a ByKey) Less(i, j int) bool { return a[i].Key < a[j].Key }
func Worker(mapf func(string, string) []KeyValue,
reducef func(string, []string) string) {
var lastTaskType string
var lastTaskIndex int
id := strconv.Itoa(os.Getpid())
for {
args := Args{
WorkerId: id,
LastTaskType: lastTaskType,
LastTaskIndex: lastTaskIndex,
}
reply := Reply{}
call("Coordinator.RpcHandler", &args, &reply)
log.Printf("Worker: receive Coordinator's reply %v\n", reply)
switch reply.TaskType {
case MAP:
mapTask(mapf, &reply, id)
case REDUCE:
reduceTask(reducef, &reply, id)
case WAIT:
time.Sleep(1 * time.Second)
case COMPLETE:
log.Printf("MR Task finished! Worker exit.\n")
return
}
lastTaskType = reply.TaskType
lastTaskIndex = reply.TaskIndex
}
}
func mapTask(mapf func(string, string) []KeyValue, reply *Reply, workerId string) {
filename := reply.Filename
log.Printf("Worker-%s get a map task, read file content from: %v\n", workerId, filename)
file, err := os.Open(filename)
if err != nil {
log.Fatalf("Map Task: cannot open %v", filename)
}
content, err := ioutil.ReadAll(file)
if err != nil {
log.Fatalf("Map Task: cannot read %v", filename)
}
err = file.Close()
if err != nil {
log.Fatalf("Map Task: cannot close %v", filename)
}
kva := mapf(filename, string(content))
buckets := make(map[int][]KeyValue)
for _, kv := range kva {
index := ihash(kv.Key) % reply.NReduce
buckets[index] = append(buckets[index], kv)
}
for i := 0; i < reply.NReduce; i++ {
ofile, _ := os.Create(TempMapOutFile(workerId, reply.TaskIndex, i))
for _, kv := range buckets[i] {
_, err := fmt.Fprintf(ofile, "%v\t%v\n", kv.Key, kv.Value)
if err != nil {
log.Printf("Map Task: can't write some data into file " + ofile.Name())
}
}
err := ofile.Close()
if err != nil {
log.Printf("Map Task: can't close file " + ofile.Name())
}
}
}
func reduceTask(reducef func(string, []string) string, reply *Reply, workerId string) {
var lines []string
for i := 0; i < reply.NMap; i++ {
filename := FinalMapOutFile(i, reply.TaskIndex)
file, err := os.Open(filename)
if err != nil {
log.Fatalf("Reduce Task: cannot read %v", filename)
}
content, err := ioutil.ReadAll(file)
if err != nil {
log.Fatalf("Reduce Task: cannot read %v", filename)
}
err = file.Close()
if err != nil {
log.Fatalf("Reduce Task: cannot close %v", filename)
}
lines = append(lines, strings.Split(string(content), "\n")...)
}
var kva []KeyValue
for _, line := range lines {
if strings.TrimSpace(line) == "" {
continue
}
seg := strings.Split(line, "\t")
kva = append(kva, KeyValue{Key: seg[0], Value: seg[1]})
}
sort.Sort(ByKey(kva))
ofile, _ := os.Create(TempReduceOutFile(workerId, reply.TaskIndex))
i := 0
for i < len(kva) {
j := i + 1
for j < len(kva) && kva[j].Key == kva[i].Key {
j++
}
var values []string
for k := i; k < j; k++ {
values = append(values, kva[k].Value)
}
output := reducef(kva[i].Key, values)
_, err := fmt.Fprintf(ofile, "%v %v\n", kva[i].Key, output)
if err != nil {
log.Printf("Map Task: can't write some data into file " + ofile.Name())
}
i = j
}
err := ofile.Close()
if err != nil {
log.Printf("Map Task: can't close file " + ofile.Name())
}
}
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