Go有状态的goroutines实例

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：/tutorial/detail-5562.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]