go實例之輕量級線程goroutine、通道channel與select

1、goroutine線程

　　goroutine是一個輕量級的執行線程。假設有一個函數調用f(s)，要在goroutine中調用此函數，請使用go f(s)。 這個新的goroutine將與調用同時執行。

　　示例代碼如下：

package main

import "fmt"

func f(from string) {
    for i := 0; i < 3; i++ {
        fmt.Println(from, ":", i)
    }
}

func main() {

    // Suppose we have a function call `f(s)`. Here's how
    // we'd call that in the usual way, running it
    // synchronously.
    f("direct")

    // To invoke this function in a goroutine, use
    // `go f(s)`. This new goroutine will execute
    // concurrently with the calling one.
    go f("goroutine")

    // You can also start a goroutine for an anonymous
    // function call.
    go func(msg string) {
        fmt.Println(msg)
    }("going")

    // Our two function calls are running asynchronously in
    // separate goroutines now, so execution falls through
    // to here. This `Scanln` code requires we press a key
    // before the program exits.
    var input string
    fmt.Scanln(&input)
    fmt.Println("done")
}

　　執行上面代碼，將得到以下輸出結果

direct : 0
direct : 1
direct : 2
goroutine : 0
goroutine : 1
goroutine : 2
going

2、通道

　　通道是連接並發goroutine的管道。可以從一個goroutine向通道發送值，並在另一個goroutine中接收到這些值。

package main

import "fmt"

func main() {

    // Create a new channel with `make(chan val-type)`.
    // Channels are typed by the values they convey.
    messages := make(chan string)

    // _Send_ a value into a channel using the `channel <-`
    // syntax. Here we send `"ping"`  to the `messages`
    // channel we made above, from a new goroutine.
    go func() { messages <- "ping" }()//使用"<-"向通道發送消息

    // The `<-channel` syntax _receives_ a value from the
    // channel. Here we'll receive the `"ping"` message
    // we sent above and print it out.
    msg := <-messages//"從通道讀取數據"
    fmt.Println(msg)
}

 　　默認情況下，通道是未緩沖的，意味着如果有相應的接收(<- chan)准備好接收發送的值，它們將只接受發送(chan <- )。使用make的第二個參數指定緩沖大小

package main

import "fmt"

func main() {

    // Here we `make` a channel of strings buffering up to
    // 2 values.
    messages := make(chan string, 2)

    // Because this channel is buffered, we can send these
    // values into the channel without a corresponding
    // concurrent receive.
    messages <- "buffered"
    messages <- "channel"

    // Later we can receive these two values as usual.
    fmt.Println(<-messages)
    fmt.Println(<-messages)
}

3、通道同步

package main

import "fmt"
import "time"

// This is the function we'll run in a goroutine. The
// `done` channel will be used to notify another
// goroutine that this function's work is done.
func worker(done chan bool) {
    fmt.Print("working...")
    time.Sleep(time.Second)
    fmt.Println("done")

    // Send a value to notify that we're done.
    done <- true
}

func main() {

    // Start a worker goroutine, giving it the channel to
    // notify on.
    done := make(chan bool, 1)
    go worker(done)

    // Block until we receive a notification from the
    // worker on the channel.
    <-done
}

　　當使用通道作為函數參數時，可以指定通道是否僅用於發送或接收值。這種特殊性增加了程序的類型安全性。chan<-表示發送，<-chan表示接收

4、select

　　每個通道將在一段時間后開始接收值，以模擬阻塞在並發goroutines中執行的RPC操作。我們將使用select同時等待這兩個值，在每個值到達時打印它們。

package main

import "time"
import "fmt"

func main() {

    // For our example we'll select across two channels.
    c1 := make(chan string)
    c2 := make(chan string)

    // Each channel will receive a value after some amount
    // of time, to simulate e.g. blocking RPC operations
    // executing in concurrent goroutines.
    go func() {
        time.Sleep(time.Second * 1)
        c1 <- "one"
    }()
    go func() {
        time.Sleep(time.Second * 2)
        c2 <- "two"
    }()

    // We'll use `select` to await both of these values
    // simultaneously, printing each one as it arrives.
    for i := 0; i < 2; i++ {
        select {
        case msg1 := <-c1:
            fmt.Println("received", msg1)
        case msg2 := <-c2:
            fmt.Println("received", msg2)
        }
    }
}

5、相關文章

　　Go超時（timeouts）實例

　　Go非阻塞通道操作實例：使用select和default子句來實現非阻塞發送，接收

　　Go關閉通道實例：close直接關閉通道

　　Go通道范圍實例：通道關閉了，還可以接收通道中的數據

 

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