errgroup

Documentation

Overview

Package errgroup 来源：kratos:https://github.com/go-kratos/kratos/blob/v1.0.0/pkg/sync/errgroup/errgroup.go

Package errgroup provides synchronization, error propagation, and Context errgroup 包为一组子任务的 goroutine 提供了 goroutine 同步,错误取消功能.

errgroup 包含三种常用方式

1、直接使用 此时不会因为一个任务失败导致所有任务被 cancel:

g := &errgroup.Group{}
g.Go(func(ctx context.Context) {
	// NOTE: 此时 ctx 为 context.Background()
	// do something
})

2、WithContext 使用 WithContext 时不会因为一个任务失败导致所有任务被 cancel:

g := errgroup.WithContext(ctx)
g.Go(func(ctx context.Context) {
	// NOTE: 此时 ctx 为 errgroup.WithContext 传递的 ctx
	// do something
})

3、WithCancel 使用 WithCancel 时如果有一个人任务失败会导致所有*未进行或进行中*的任务被 cancel:

g := errgroup.WithCancel(ctx)
g.Go(func(ctx context.Context) {
	// NOTE: 此时 ctx 是从 errgroup.WithContext 传递的 ctx 派生出的 ctx
	// do something
})

设置最大并行数 GOMAXPROCS 对以上三种使用方式均起效 NOTE: 由于 errgroup 实现问题,设定 GOMAXPROCS 的 errgroup 需要立即调用 Wait() 例如:

g := errgroup.WithCancel(ctx)
g.GOMAXPROCS(2)
// task1
g.Go(func(ctx context.Context) {
	fmt.Println("task1")
})
// task2
g.Go(func(ctx context.Context) {
	fmt.Println("task2")
})
// task3
g.Go(func(ctx context.Context) {
	fmt.Println("task3")
})
// NOTE: 此时设置的 GOMAXPROCS 为2, 添加了三个任务 task1, task2, task3 此时 task3 是不会运行的!
// 只有调用了 Wait task3 才有运行的机会
g.Wait() // task3 运行

Index

• type Group
  • func WithCancel(ctx context.Context) *Group
  • func WithContext(ctx context.Context) *Group
  • func (g *Group) GOMAXPROCS(n int)
  • func (g *Group) Go(f func(ctx context.Context) error)
  • func (g *Group) Wait() error

Examples

• Group (Cancel)
• Group (Ctx)
• Group (Group)
• Group (JustErrors)
• Group (Maxproc)
• Group (Parallel)

Types

type Group

type Group struct {
	// contains filtered or unexported fields
}

A Group is a collection of goroutines working on subtasks that are part of the same overall task.

A zero Group is valid and does not cancel on error.

Example (Cancel)

g := WithCancel(context.Background())
g.Go(fakeRunTask)
g.Go(fakeRunTask)
if err := g.Wait(); err != nil {
	// handle err
}

Example (Ctx)

g := WithContext(context.Background())
g.Go(fakeRunTask)
g.Go(fakeRunTask)
if err := g.Wait(); err != nil {
	// handle err
}

Example (Group)

g := Group{}
g.Go(fakeRunTask)
g.Go(fakeRunTask)
if err := g.Wait(); err != nil {
	// handle err
}

Example (JustErrors)

JustErrors illustrates the use of a Group in place of a sync.WaitGroup to simplify goroutine counting and error handling. This example is derived from the sync.WaitGroup example at https://golang.org/pkg/sync/#example_WaitGroup.

var g Group
var urls = []string{
	"http://www.golang.org/",
	"http://www.google.com/",
	"http://www.somestupidname.com/",
}
for _, url := range urls {
	// Launch a goroutine to fetch the URL.
	url := url // https://golang.org/doc/faq#closures_and_goroutines
	g.Go(func(context.Context) error {
		// Fetch the URL.
		resp, err := http.Get(url)
		if err == nil {
			resp.Body.Close()
		}
		return err
	})
}
// Wait for all HTTP fetches to complete.
if err := g.Wait(); err == nil {
	fmt.Println("Successfully fetched all URLs.")
}

Example (Maxproc)

g := Group{}
// set max concurrency
g.GOMAXPROCS(2)
g.Go(fakeRunTask)
g.Go(fakeRunTask)
if err := g.Wait(); err != nil {
	// handle err
}

Example (Parallel)

Parallel illustrates the use of a Group for synchronizing a simple parallel task: the "Google Search 2.0" function from https://talks.golang.org/2012/concurrency.slide#46, augmented with a Context and error-handling.

Google := func(ctx context.Context, query string) ([]Result, error) {
	g := WithContext(ctx)

	searches := []Search{Web, Image, Video}
	results := make([]Result, len(searches))
	for i, search := range searches {
		i, search := i, search // https://golang.org/doc/faq#closures_and_goroutines
		g.Go(func(context.Context) error {
			result, err := search(ctx, query)
			if err == nil {
				results[i] = result
			}
			return err
		})
	}
	if err := g.Wait(); err != nil {
		return nil, err
	}
	return results, nil
}

results, err := Google(context.Background(), "golang")
if err != nil {
	fmt.Fprintln(os.Stderr, err)
	return
}
for _, result := range results {
	fmt.Println(result)
}

Output:

web result for "golang"
image result for "golang"
video result for "golang"

func WithCancel

func WithCancel(ctx context.Context) *Group

WithCancel create a new Group and an associated Context derived from ctx.

given function from Go will receive context derived from this ctx, The derived Context is canceled the first time a function passed to Go returns a non-nil error or the first time Wait returns, whichever occurs first.

func WithContext

func WithContext(ctx context.Context) *Group

WithContext create a Group. given function from Go will receive this context,

func (*Group) GOMAXPROCS

func (g *Group) GOMAXPROCS(n int)

GOMAXPROCS set max goroutine to work.

func (*Group) Go

func (g *Group) Go(f func(ctx context.Context) error)

Go calls the given function in a new goroutine.

The first call to return a non-nil error cancels the group; its error will be returned by Wait.

func (*Group) Wait

func (g *Group) Wait() error

Wait blocks until all function calls from the Go method have returned, then returns the first non-nil error (if any) from them.