在前面的示例中，我们使用显式锁定互斥体来同步对多个goroutine的共享状态的访问。 另一个选项是使用goroutine和通道的内置同步功能来实现相同的结果。这种基于通道的方法与Go的共享内存的想法一致，通过沟通，拥有每个数据的goroutine恰好只有1个。
在这个例子中，状态将由单个goroutine拥有。这将保证数据不会因并发访问而损坏。为了读或写状态，其他goroutine将发送消息到拥有的goroutine并接收相应的回复。这些readOp和writeOp结构封装了这些请求，并拥有一个goroutine响应的方法。
和以前一样，我们将计算执行的操作数。
读写通道将被其他goroutine分别用来发出读和写请求。
这里是拥有状态的goroutine，它是一个如前面示例中的映射，但现在对状态goroutine是私有的。这个goroutine在读取和写入通道时重复选择，在请求到达时响应请求。 通过首先执行所请求的操作，然后在响应信道上发送值以指示成功(以及在读取的情况下的期望值)来执行响应。
这里启动了100个goroutine来通过读取通道向状态拥有的goroutine发出读取。每次读取都需要构造一个readOp，通过读取通道发送readOp，并通过提供的resp通道接收结果。
也使用类似的方法开始10个写操作。让goroutine工作一秒钟。最后，捕获和报告操作计数。
运行程序显示，基于goroutine的状态管理示例程序，完成了大约80,000次操作。
对于这种特殊情况，基于goroutine的方法比基于互斥的方法更多一些。它在某些情况下可能是有用的，例如，当有其他通道涉及或管理多个此类互斥体将容易出错。应该使用最自然的方法，有助于理解程序。
所有的示例代码，都放在
F:\worksp\golang目录下。安装Go编程环境请参考：http://www.yiibai.com/go/go_environment.html
stateful-goroutines.go的完整代码如下所示 -
package main
import (
"fmt"
"math/rand"
"sync/atomic"
"time"
)
// In this example our state will be owned by a single
// goroutine. This will guarantee that the data is never
// corrupted with concurrent access. In order to read or
// write that state, other goroutines will send messages
// to the owning goroutine and receive corresponding
// replies. These `readOp` and `writeOp` `struct`s
// encapsulate those requests and a way for the owning
// goroutine to respond.
type readOp struct {
key int
resp chan int
}
type writeOp struct {
key int
val int
resp chan bool
}
func main() {
// As before we'll count how many operations we perform.
var readOps uint64 = 0
var writeOps uint64 = 0
// The `reads` and `writes` channels will be used by
// other goroutines to issue read and write requests,
// respectively.
reads := make(chan *readOp)
writes := make(chan *writeOp)
// Here is the goroutine that owns the `state`, which
// is a map as in the previous example but now private
// to the stateful goroutine. This goroutine repeatedly
// selects on the `reads` and `writes` channels,
// responding to requests as they arrive. A response
// is executed by first performing the requested
// operation and then sending a value on the response
// channel `resp` to indicate success (and the desired
// value in the case of `reads`).
go func() {
var state = make(map[int]int)
for {
select {
case read := <-reads:
read.resp <- state[read.key]
case write := <-writes:
state[write.key] = write.val
write.resp <- true
}
}
}()
// This starts 100 goroutines to issue reads to the
// state-owning goroutine via the `reads` channel.
// Each read requires constructing a `readOp`, sending
// it over the `reads` channel, and the receiving the
// result over the provided `resp` channel.
for r := 0; r < 100; r++ {
go func() {
for {
read := &readOp{
key: rand.Intn(5),
resp: make(chan int)}
reads <- read
<-read.resp
atomic.AddUint64(&readOps, 1)
time.Sleep(time.Millisecond)
}
}()
}
// We start 10 writes as well, using a similar
// approach.
for w := 0; w < 10; w++ {
go func() {
for {
write := &writeOp{
key: rand.Intn(5),
val: rand.Intn(100),
resp: make(chan bool)}
writes <- write
<-write.resp
atomic.AddUint64(&writeOps, 1)
time.Sleep(time.Millisecond)
}
}()
}
// Let the goroutines work for a second.
time.Sleep(time.Second)
// Finally, capture and report the op counts.
readOpsFinal := atomic.LoadUint64(&readOps)
fmt.Println("readOps:", readOpsFinal)
writeOpsFinal := atomic.LoadUint64(&writeOps)
fmt.Println("writeOps:", writeOpsFinal)
}
执行上面代码，将得到以下输出结果 -
F:\worksp\golang>go run mutexes.go
readOps: 84546
writeOps: 8473
state: map[0:99 3:3 4:62 1:18 2:89]
