Go 之常用并发学习

Looooking2024-04-26 1:01

在 Go语言实战 中看到有些并发相关的例子，讲解得也比较详细，于是乎写来加深下印象。

无缓冲通道

无缓冲通道在接收前没有能力保存任何值。我自己找了书上的示例来加深一下印象。

模拟网球比赛

Go 复制代码 
package main

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

var (
	wg sync.WaitGroup
)

func init() {
	rand.Seed(time.Now().UnixNano()) // 让每次运行生成的随机数不相同
}

func main() {
	count := make(chan int)
	wg.Add(2)
	go player("Nadal", count)
	go player("Looking", count)

	count <- 1
	wg.Wait()
}

func player(name string, count chan int) {
	defer wg.Done()

	for {
		ball, ok := <-count
		if !ok {
			fmt.Printf("Player %s Win\n", name)
			return
		}
		n := rand.Intn(100)
		if n%13 == 0 {
			fmt.Printf("Player %s Missed\n", name)
			close(count)
			return
		}
		fmt.Printf("Player %s Hit %d\n", name, ball)
		count <- ball
	}
}

模拟接力赛

接力赛中，接力棒只能在一个人手中。

Go 复制代码 
package main

import (
	"fmt"
	"sync"
	"time"
)

var (
	wg sync.WaitGroup
)


func main() {
	baton := make(chan int)
	wg.Add(1)
	go Runner(baton)
	baton <- 1
	wg.Wait()
}

func Runner(baton chan int)  {
	var newRunner int
	runner := <- baton
	fmt.Printf("Runner %d Running with baton\n", runner)
	if runner != 4 {
		newRunner = runner + 1
		fmt.Printf("Runner %d to the line\n", newRunner)
		go Runner(baton)
	}
	time.Sleep(100 * time.Millisecond)
	if runner == 4 {
		fmt.Printf("Runner %d finished, Race over\n", runner)
		wg.Done()
		return
	}
	fmt.Printf("Runner %d Exchange with runner %d \n", runner, newRunner)
	baton <- newRunner
}
Go 复制代码 
Runner 1 Running with baton
Runner 2 to the line
Runner 1 Exchange with runner 2 
Runner 2 Running with baton
Runner 3 to the line
Runner 2 Exchange with runner 3 
Runner 3 Running with baton
Runner 4 to the line
Runner 3 Exchange with runner 4 
Runner 4 Running with baton
Runner 4 finished, Race over

有缓冲通道

缓冲通道不强制发送和接收同时完成。

复制代码 
当通道关闭后，goroutine 依旧可以从通道接收数据，但是不能再向通道里发送数据。能够从已经关闭的通道接收数据这一点非常重要，因为这允许通 道关闭后依旧能取出其中缓冲的全部值，而不会有数据丢失。从一个已经关闭且没有数据的通道 里获取数据，总会立刻返回，并返回一个通道类型的零值。如果在获取通道时还加入了可选的标 志，就能得到通道的状态信息。

模拟任务分发和处理

Go 复制代码 
package main

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

const (
	numberGoroutines = 4
	taskLoad         = 10
)

var wg sync.WaitGroup

func init() {
	rand.Seed(time.Now().UnixNano())
}

func main() {
	tasks := make(chan string, taskLoad)
	wg.Add(numberGoroutines)
	for gr := 1; gr <= numberGoroutines; gr++ {
		go worker(tasks, gr)
	}
	for post := 1; post <= taskLoad; post++ {
		tasks <- fmt.Sprintf("Task: %d", post)
	}
	close(tasks) // 任务发布完毕后关闭通道，关闭通道不影响其它Goroutine对已发布内容的正常接收
	wg.Wait()
}

func worker(tasks chan string, worker int) {
	defer wg.Done()

	for {
		task, ok := <-tasks
		if !ok {
			fmt.Printf("Worker: %d : Shutting down\n", worker)
			return
		}
		fmt.Printf("Worker: %d : Started %s\n", worker, task)
		sleep := rand.Int63n(100)
		time.Sleep(time.Duration(sleep) * time.Millisecond)
		fmt.Printf("Worker: %d : Completed %s\n", worker, task)
	}
}
Go 复制代码 
Worker: 4 : Started Task: 4
Worker: 2 : Started Task: 2
Worker: 3 : Started Task: 3
Worker: 1 : Started Task: 1
Worker: 3 : Completed Task: 3
Worker: 3 : Started Task: 5
Worker: 2 : Completed Task: 2
Worker: 2 : Started Task: 6
Worker: 1 : Completed Task: 1
Worker: 1 : Started Task: 7
Worker: 1 : Completed Task: 7
Worker: 1 : Started Task: 8
Worker: 3 : Completed Task: 5
Worker: 3 : Started Task: 9
Worker: 4 : Completed Task: 4
Worker: 4 : Started Task: 10
Worker: 2 : Completed Task: 6
Worker: 2 : Shutting down
Worker: 3 : Completed Task: 9
Worker: 3 : Shutting down
Worker: 1 : Completed Task: 8
Worker: 1 : Shutting down
Worker: 4 : Completed Task: 10
Worker: 4 : Shutting down

runner

runner 包用于展示如何使用通道来监视程序的执行时间，如果程序运行时间太长，也可以

用runner 包来终止程序。当开发需要调度后台处理任务的程序的时候，这种模式会很有用。

runner/runner.go

Go 复制代码 
package runner

import (
	"errors"
	"os"
	"os/signal"
	"time"
)

type Runner struct {
	interrupt chan os.Signal
	complete  chan error
	timeout   <-chan time.Time // 单向通道，只允许接收
	tasks     []func(int)
}

var ErrTimeout = errors.New("received timeout")
var ErrInterrupt = errors.New("received interrupt")

func New(d time.Duration) *Runner {
	return &Runner{
		interrupt: make(chan os.Signal, 1),
		complete:  make(chan error),
		timeout:   time.After(d),
	}
}

func (r *Runner) Add(tasks ...func(int)) {
	r.tasks = append(r.tasks, tasks...)
}

func (r *Runner) Start() error {
	signal.Notify(r.interrupt, os.Interrupt) // 如果有中断，会将中断信号发送到 r.interrupt
	go func() {
		r.complete <- r.run()
	}()
	select {
	case err := <-r.complete:
		return err // 如果提前中断，err 是 ErrInterrupt，正常结束则是 nil
	case <-r.timeout:
		return ErrTimeout
	}
}

func (r *Runner) run() error {
	for id, task := range r.tasks {
		if r.gotInterrupt() {
			return ErrInterrupt
		}
		task(id)
	}
	return nil
}

func (r *Runner) gotInterrupt() bool {
	select {
	case <-r.interrupt:
		signal.Stop(r.interrupt)
		return true
	default:
		return false
	}
}

main.go

Go 复制代码 
package main

import (
	"github.com/test/runner"
	"log"
	"os"
	"time"
)

const timeout = 3 * time.Second

func main() {
	log.Println("Starting work.")
	r := runner.New(timeout)
	r.Add(createTask(), createTask(), createTask())

	if err := r.Start(); err != nil {
		switch err {
		case runner.ErrTimeout:
			log.Println("Terminating due to timeout.")
			os.Exit(1)
		case runner.ErrInterrupt:
			log.Println("Terminating due to interrupt.")
			os.Exit(2)
		}
	}
	log.Println("Process ended.")
}

func createTask() func(int) {
	return func(id int) {
		log.Printf("Processor - Task #%d.", id)
		time.Sleep(time.Duration(id) * time.Second)
	}
}

超时退出

Go 复制代码 
2024/04/21 17:26:30 Starting work.
2024/04/21 17:26:30 Processor - Task #0.
2024/04/21 17:26:30 Processor - Task #1.
2024/04/21 17:26:31 Processor - Task #2.
2024/04/21 17:26:33 Terminating due to timeout.

中断退出

Go 复制代码 
2024/04/21 17:28:18 Starting work.
2024/04/21 17:28:18 Processor - Task #0.
2024/04/21 17:28:18 Processor - Task #1.
2024/04/21 17:28:19 Terminating due to interrupt.

正常退出

Go 复制代码 
2024/04/21 17:30:40 Starting work.
2024/04/21 17:30:40 Processor - Task #0.
2024/04/21 17:30:40 Processor - Task #1.
2024/04/21 17:30:41 Processor - Task #2.
2024/04/21 17:30:43 Process ended.

pool

pool 使用有缓冲通道实现资源池。

pool/pool.go

Go 复制代码 
package pool

import (
	"errors"
	"io"
	"log"
	"sync"
)

type Pool struct {
	m         sync.Mutex
	resources chan io.Closer
	factory   func() (io.Closer, error)
	closed    bool
}

var ErrPoolClosed = errors.New("pool has been closed")

func New(fn func() (io.Closer, error), size uint) (*Pool, error) {
	if size <= 0 {
		return nil, errors.New("size value too small")
	}
	return &Pool{
		resources: make(chan io.Closer, size),
		factory:   fn,
	}, nil
}

func (p *Pool) Acquire() (io.Closer, error) {
	select {
	case r, ok := <-p.resources:
		log.Println("Acquire:", "Shared resource")
		if !ok {
			return nil, ErrPoolClosed
		}
		return r, nil
	default:
		log.Println("Acquire:", "New resource")
		return p.factory()
	}
}

func (p *Pool) Release(r io.Closer) {
	p.m.Lock()
	defer p.m.Unlock()
	if p.closed {
		r.Close()
		return
	}
	select {
	case p.resources <- r:
		log.Println("Release:", "In queue")
	default:
		log.Println("Release:", "Closing")
		r.Close()
	}
}

func (p *Pool) Close() {
	p.m.Lock()
	defer p.m.Unlock()
	if p.closed {
		return
	}
	p.closed = true
	close(p.resources)
	for r := range p.resources {
		r.Close()
	}
}

main.go

Go 复制代码 
package main

import (
	"github.com/test/pool"
	"io"
	"log"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"
)

const (
	maxGoroutines   = 5
	pooledResources = 2
)

type dbConnection struct {
	ID int32
}

func (dbConn *dbConnection) Close() error {
	log.Println("Close: Connection", dbConn.ID)
	return nil
}

var idCounter int32

func createConnection() (io.Closer, error) {
	id := atomic.AddInt32(&idCounter, 1)
	log.Println("Create: New Connection", id)

	return &dbConnection{id}, nil
}

func main() {
	var wg sync.WaitGroup
	wg.Add(maxGoroutines)

	p, err := pool.New(createConnection, pooledResources)
	if err != nil {
		log.Println(err)
	}

	for query := 0; query < maxGoroutines; query++ {
		go func(q int) {
			defer wg.Done()
			performQueries(q, p)
		}(query)
	}
	wg.Wait()
	log.Println("Shutdown program")
	p.Close()
}

func performQueries(query int, p *pool.Pool) {
	conn, err := p.Acquire()
	if err != nil {
		log.Println(err)
		return
	}
	defer p.Release(conn)
	time.Sleep(time.Duration(rand.Intn(1000)) * time.Millisecond)
	log.Printf("QID[%d] CID[%d]\n", query, conn.(*dbConnection).ID)
}

运行结果

Go 复制代码 
2024/04/21 20:29:20 Acquire: New resource
2024/04/21 20:29:20 Create: New Connection 1
2024/04/21 20:29:20 Acquire: New resource
2024/04/21 20:29:20 Acquire: New resource
2024/04/21 20:29:20 Create: New Connection 3
2024/04/21 20:29:20 Acquire: New resource
2024/04/21 20:29:20 Create: New Connection 4
2024/04/21 20:29:20 Create: New Connection 2
2024/04/21 20:29:20 Acquire: New resource
2024/04/21 20:29:20 Create: New Connection 5
2024/04/21 20:29:20 QID[0] CID[2]
2024/04/21 20:29:20 Release: In queue
2024/04/21 20:29:20 QID[2] CID[5]
2024/04/21 20:29:20 Release: In queue
2024/04/21 20:29:20 QID[4] CID[1]
2024/04/21 20:29:20 Release: Closing
2024/04/21 20:29:20 Close: Connection 1
2024/04/21 20:29:21 QID[1] CID[4]
2024/04/21 20:29:21 Release: Closing
2024/04/21 20:29:21 Close: Connection 4
2024/04/21 20:29:21 QID[3] CID[3]
2024/04/21 20:29:21 Release: Closing
2024/04/21 20:29:21 Close: Connection 3
2024/04/21 20:29:21 Shutdown program
2024/04/21 20:29:21 Close: Connection 2
2024/04/21 20:29:21 Close: Connection 5

work

work 使用无缓冲通道创建资源池。work 新建时就生成指定个数 goroutine 循环等待（无缓冲通道无数据阻塞）消费任务，然后主线程再分发相应任务到通道，消费 goroutine 再继续执行消费任务。

work/work.go

Go 复制代码 
package work

import "sync"

type Worker interface {
	Task()
}

type Pool struct {
	work chan Worker
	wg   sync.WaitGroup
}

func New(maxGoroutines int) *Pool {
	p := Pool{
		work: make(chan Worker),
	}
	p.wg.Add(maxGoroutines)
	for i := 0; i < maxGoroutines; i++ {
		go func() {
			defer p.wg.Done()
			for w := range p.work { // 如果 work 关闭，for range 循环结束
				w.Task()
			}
		}()
	}
	return &p
}

func (p *Pool) Run(w Worker) {
	p.work <- w
}

func (p *Pool) Shutdown() {
	close(p.work) // 关闭通道，避免 New 产生的 goroutine 一直阻塞不退出
	p.wg.Wait()
}

main.go

Go 复制代码 
package main

import (
	"github.com/test/work"
	"log"
	"sync"
	"time"
)

var names = []string{
	"steve",
	"jason",
	"looking",
}

type namePrinter struct {
	name string
}

func (m *namePrinter) Task() {
	log.Println(m.name)
	time.Sleep(time.Second)
}

const times = 3

func main() {
	p := work.New(2)

	var wg sync.WaitGroup
	wg.Add(times * len(names))
	for i := 0; i < times; i++ {
		for _, name := range names {
			np := namePrinter{name: name}
			go func() {
				defer wg.Done()
				p.Run(&np)
			}()
		}
	}
	wg.Wait()
	p.Shutdown()
}

运行结果

Go 复制代码 
2024/04/21 21:39:28 steve
2024/04/21 21:39:28 looking
2024/04/21 21:39:29 jason
2024/04/21 21:39:29 looking
2024/04/21 21:39:30 steve
2024/04/21 21:39:30 jason
2024/04/21 21:39:31 looking
2024/04/21 21:39:31 steve
2024/04/21 21:39:32 jason
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