go语言同步教程之条件变量

// NewCond returns a new Cond with Locker l.
func NewCond(l Locker) *Cond {
 return &Cond{L: l}
}

// A Locker represents an object that can be locked and unlocked.
type Locker interface {
 Lock()
 Unlock()
}

// Wait atomically unlocks c.L and suspends execution
// of the calling goroutine. After later resuming execution,
// Wait locks c.L before returning. Unlike in other systems,
// Wait cannot return unless awoken by Broadcast or Signal.
//
// Because c.L is not locked when Wait first resumes, the caller
// typically cannot assume that the condition is true when
// Wait returns. Instead, the caller should Wait in a loop:
//
// c.L.Lock()
// for !condition() {
//  c.Wait()
// }
// ... make use of condition ...
// c.L.Unlock()
//
func (c *Cond) Wait() {
 c.checker.check()
 t := runtime_notifyListAdd(&c.notify)
 c.L.Unlock()
 runtime_notifyListWait(&c.notify, t)
 c.L.Lock()
}

// Signal wakes one goroutine waiting on c, if there is any.
//
// It is allowed but not required for the caller to hold c.L
// during the call.
func (c *Cond) Signal() {
 c.checker.check()
 runtime_notifyListNotifyOne(&c.notify)
}

// Broadcast wakes all goroutines waiting on c.
//
// It is allowed but not required for the caller to hold c.L
// during the call.
func (c *Cond) Broadcast() {
 c.checker.check()
 runtime_notifyListNotifyAll(&c.notify)
}

if tlsConn, ok := c.rwc.(*tls.Conn); ok {
  if d := c.server.ReadTimeout; d != 0 {
   c.rwc.SetReadDeadline(time.Now().Add(d))
  }
  if d := c.server.WriteTimeout; d != 0 {
   c.rwc.SetWriteDeadline(time.Now().Add(d))
  }
  if err := tlsConn.Handshake(); err != nil {
   c.server.logf("http: TLS handshake error from %s: %v", c.rwc.RemoteAddr(), err)
   return
  }
  c.tlsState = new(tls.ConnectionState)
  *c.tlsState = tlsConn.ConnectionState()
  if proto := c.tlsState.NegotiatedProtocol; validNPN(proto) {
   if fn := c.server.TLSNextProto[proto]; fn != nil {
    h := initNPNRequest{tlsConn, serverHandler{c.server}}
    fn(c.server, tlsConn, h)
   }
   return
  }
 }

func (c *Conn) Handshake() error {
 c.handshakeMutex.Lock()
 defer c.handshakeMutex.Unlock()

 for {
  if err := c.handshakeErr; err != nil {
   return err
  }
  if c.handshakeComplete {
   return nil
  }
  if c.handshakeCond == nil {
   break
  }

  c.handshakeCond.Wait()
 }

 c.handshakeCond = sync.NewCond(&c.handshakeMutex)
 c.handshakeMutex.Unlock()

 c.in.Lock()
 defer c.in.Unlock()

 c.handshakeMutex.Lock()

 if c.handshakeErr != nil || c.handshakeComplete {
  panic("handshake should not have been able to complete after handshakeCond was set")
 }

 if c.isClient {
  c.handshakeErr = c.clientHandshake()
 } else {
  c.handshakeErr = c.serverHandshake()
 }
 if c.handshakeErr == nil {
  c.handshakes++
 } else {
  c.flush()
 }

 if c.handshakeErr == nil && !c.handshakeComplete {
  panic("handshake should have had a result.")
 }

 c.handshakeCond.Broadcast()
 c.handshakeCond = nil

 return c.hand

package main

import (
 "bytes"
 "fmt"
 "io"
 "sync"
 "time"
)

type MyDataBucket struct {
 br  *bytes.Buffer
 gmutex *sync.RWMutex
 rcond *sync.Cond //读操作需要用到的条件变量
}

func NewDataBucket() *MyDataBucket {
 buf := make([]byte, 0)
 db := &MyDataBucket{
  br:  bytes.NewBuffer(buf),
  gmutex: new(sync.RWMutex),
 }
 db.rcond = sync.NewCond(db.gmutex.RLocker())
 return db
}

func (db *MyDataBucket) Read(i int) {
 db.gmutex.RLock()
 defer db.gmutex.RUnlock()
 var data []byte
 var d byte
 var err error
 for {
  //读取一个字节
  if d, err = db.br.ReadByte(); err != nil {
   if err == io.EOF {
    if string(data) != "" {
     fmt.Printf("reader-%d: %s\n", i, data)
    }
    db.rcond.Wait()
    data = data[:0]
    continue
   }
  }
  data = append(data, d)
 }
}

func (db *MyDataBucket) Put(d []byte) (int, error) {
 db.gmutex.Lock()
 defer db.gmutex.Unlock()
 //写入一个数据块
 n, err := db.br.Write(d)
 db.rcond.Broadcast()
 return n, err
}

func main() {
 db := NewDataBucket()

 go db.Read(1)

 go db.Read(2)

 for i := 0; i < 10; i++ {
  go func(i int) {
   d := fmt.Sprintf("data-%d", i)
   db.Put([]byte(d))
  }(i)
  time.Sleep(100 * time.Millisecond)
 }
}

func (c *Cond) Wait() {
 c.checker.check()
 t := runtime_notifyListAdd(&c.notify)
 c.L.Unlock()
 runtime_notifyListWait(&c.notify, t)
 c.L.Lock()
}