《Go语言实战》学习笔记——有缓冲的通道代码实战

第6章 并发

6.5 通道

6.5.2 有缓冲的通道

概念

有缓冲的通道（buffered channel）是一种在被接收前能存储一个或者多个值的通道。这种类
型的通道并不强制要求 goroutine 之间必须同时完成发送和接收。通道会阻塞发送和接收动作的条件也会不同。只有在通道中没有要接收的值时，接收动作才会阻塞。只有在通道没有可用缓冲区容纳被发送的值时，发送动作才会阻塞。这导致有缓冲的通道和无缓冲的通道之间的一个很大的不同：无缓冲的通道保证进行发送和接收的 goroutine 会在同一时间进行数据交换；有缓冲的通道没有这种保证。

代码实战

让我们看一个使用有缓冲的通道的例子，这个例子管理一组 goroutine 来接收并完成工作。
有缓冲的通道提供了一种清晰而直观的方式来实现这个功能，代码如下

// This sample program demonstrates how to use a buffered
// channel to work on multiple tasks with a predefined number
// of goroutines.
package main

import (
	"fmt"
	"math/rand"
	"sync"
	"time"
)

const (
	numberGoroutines = 4  // Number of goroutines to use.
	taskLoad         = 10 // Amount of work to process.
)

// wg is used to wait for the program to finish.
var wg sync.WaitGroup

// init is called to initialize the package by the
// Go runtime prior to any other code being executed.
func init() {
	// Seed the random number generator.
	rand.Seed(time.Now().Unix())
}

// main is the entry point for all Go programs.
func main() {
	// Create a buffered channel to manage the task load.
	tasks := make(chan string, taskLoad)

	// Launch goroutines to handle the work.
	wg.Add(numberGoroutines)
	for gr := 1; gr <= numberGoroutines; gr++ {
		go worker(tasks, gr)
	}

	// Add a bunch of work to get done.
	for post := 1; post <= taskLoad; post++ {
		tasks <- fmt.Sprintf("Task : %d", post)
	}

	// Close the channel so the goroutines will quit
	// when all the work is done.
	close(tasks)

	// Wait for all the work to get done.
	wg.Wait()
}

// worker is launched as a goroutine to process work from
// the buffered channel.
func worker(tasks chan string, worker int) {
	// Report that we just returned.
	defer wg.Done()

	for {
		// Wait for work to be assigned.
		task, ok := <-tasks
		if !ok {
			// This means the channel is empty and closed.
			fmt.Printf("Worker: %d : Shutting Down\n", worker)
			return
		}

		// Display we are starting the work.
		fmt.Printf("Worker: %d : Started %s\n", worker, task)

		// Randomly wait to simulate work time.
		sleep := rand.Int63n(100)
		time.Sleep(time.Duration(sleep) * time.Millisecond)

		// Display we finished the work.
		fmt.Printf("Worker: %d : Completed %s\n", worker, task)
	}
}

运行结果

go run listing24.go 
Worker: 1 : Started Task : 1
Worker: 3 : Started Task : 3
Worker: 4 : Started Task : 4
Worker: 2 : Started Task : 2
Worker: 3 : Completed Task : 3
Worker: 3 : Started Task : 5
Worker: 4 : Completed Task : 4
Worker: 4 : Started Task : 6
Worker: 1 : Completed Task : 1
Worker: 1 : Started Task : 7
Worker: 3 : Completed Task : 5
Worker: 3 : Started Task : 8
Worker: 1 : Completed Task : 7
Worker: 1 : Started Task : 9
Worker: 2 : Completed Task : 2
Worker: 2 : Started Task : 10
Worker: 4 : Completed Task : 6
Worker: 4 : Shutting Down
Worker: 3 : Completed Task : 8
Worker: 3 : Shutting Down
Worker: 2 : Completed Task : 10
Worker: 2 : Shutting Down
Worker: 1 : Completed Task : 9
Worker: 1 : Shutting Down

具体代码的中文注释和解释如下