go实例之轻量级线程goroutine、通道channel与select

1、goroutine线程

　　goroutine是一个轻量级的执行线程。假设有一个函数调用f(s)，要在goroutine中调用此函数，请使用go f(s)。这个新的goroutine将与调用同时执行。

　　示例代码如下：

 1 package main
 2 
 3 import "fmt"
 4 
 5 func f(from string) {
 6     for i := 0; i < 3; i++ {
 7         fmt.Println(from, ":", i)
 8     }
 9 }
10 
11 func main() {
12 
13     // Suppose we have a function call `f(s)`. Here's how
14     // we'd call that in the usual way, running it
15     // synchronously.
16     f("direct")
17 
18     // To invoke this function in a goroutine, use
19     // `go f(s)`. This new goroutine will execute
20     // concurrently with the calling one.
21     go f("goroutine")
22 
23     // You can also start a goroutine for an anonymous
24     // function call.
25     go func(msg string) {
26         fmt.Println(msg)
27     }("going")
28 
29     // Our two function calls are running asynchronously in
30     // separate goroutines now, so execution falls through
31     // to here. This `Scanln` code requires we press a key
32     // before the program exits.
33     var input string
34     fmt.Scanln(&input)
35     fmt.Println("done")
36 }

　　执行上面代码，将得到以下输出结果

1 direct : 0
2 direct : 1
3 direct : 2
4 goroutine : 0
5 goroutine : 1
6 goroutine : 2
7 going

2、通道

　　通道是连接并发goroutine的管道。可以从一个goroutine向通道发送值，并在另一个goroutine中接收到这些值。

 1 package main
 2 
 3 import "fmt"
 4 
 5 func main() {
 6 
 7     // Create a new channel with `make(chan val-type)`.
 8     // Channels are typed by the values they convey.
 9     messages := make(chan string)
10 
11     // _Send_ a value into a channel using the `channel <-`
12     // syntax. Here we send `"ping"`  to the `messages`
13     // channel we made above, from a new goroutine.
14     go func() { messages <- "ping" }()//使用"<-"向通道发送消息
15 
16     // The `<-channel` syntax _receives_ a value from the
17     // channel. Here we'll receive the `"ping"` message
18     // we sent above and print it out.
19     msg := <-messages//"从通道读取数据"
20     fmt.Println(msg)
21 }

　　默认情况下，通道是未缓冲的，意味着如果有相应的接收(<- chan)准备好接收发送的值，它们将只接受发送(chan <- )。使用make的第二个参数指定缓冲大小

 1 package main
 2 
 3 import "fmt"
 4 
 5 func main() {
 6 
 7     // Here we `make` a channel of strings buffering up to
 8     // 2 values.
 9     messages := make(chan string, 2)
10 
11     // Because this channel is buffered, we can send these
12     // values into the channel without a corresponding
13     // concurrent receive.
14     messages <- "buffered"
15     messages <- "channel"
16 
17     // Later we can receive these two values as usual.
18     fmt.Println(<-messages)
19     fmt.Println(<-messages)
20 }

3、通道同步

 1 package main
 2 
 3 import "fmt"
 4 import "time"
 5 
 6 // This is the function we'll run in a goroutine. The
 7 // `done` channel will be used to notify another
 8 // goroutine that this function's work is done.
 9 func worker(done chan bool) {
10     fmt.Print("working...")
11     time.Sleep(time.Second)
12     fmt.Println("done")
13 
14     // Send a value to notify that we're done.
15     done <- true
16 }
17 
18 func main() {
19 
20     // Start a worker goroutine, giving it the channel to
21     // notify on.
22     done := make(chan bool, 1)
23     go worker(done)
24 
25     // Block until we receive a notification from the
26     // worker on the channel.
27     <-done
28 }

　　当使用通道作为函数参数时，可以指定通道是否仅用于发送或接收值。这种特殊性增加了程序的类型安全性。chan<-表示发送，<-chan表示接收

4、select

　　每个通道将在一段时间后开始接收值，以模拟阻塞在并发goroutines中执行的RPC操作。我们将使用select同时等待这两个值，在每个值到达时打印它们。

 1 package main
 2 
 3 import "time"
 4 import "fmt"
 5 
 6 func main() {
 7 
 8     // For our example we'll select across two channels.
 9     c1 := make(chan string)
10     c2 := make(chan string)
11 
12     // Each channel will receive a value after some amount
13     // of time, to simulate e.g. blocking RPC operations
14     // executing in concurrent goroutines.
15     go func() {
16         time.Sleep(time.Second * 1)
17         c1 <- "one"
18     }()
19     go func() {
20         time.Sleep(time.Second * 2)
21         c2 <- "two"
22     }()
23 
24     // We'll use `select` to await both of these values
25     // simultaneously, printing each one as it arrives.
26     for i := 0; i < 2; i++ {
27         select {
28         case msg1 := <-c1:
29             fmt.Println("received", msg1)
30         case msg2 := <-c2:
31             fmt.Println("received", msg2)
32         }
33     }
34 }