Golang中使用context作为goroutine之间的控制器，例如：

package main

import (
	"context"
	"log"
	"time"
)

func UseContext(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			log.Printf("context is done with error %s", ctx.Err())
			return
		default:
			log.Printf("nothing just loop...")
			time.Sleep(time.Second * time.Duration(1))
		}
	}
}

func main() {
	ctx, cancel := context.WithCancel(context.Background())
	go UseContext(ctx)

	time.Sleep(time.Second * time.Duration(1))
	cancel()
	time.Sleep(time.Second * time.Duration(2))
}
mainUseContext
context
type Context interface {
	Deadline() (deadline time.Time, ok bool)
	Done() <-chan struct{}
	Err() error
	Value(key interface{}) interface{}
}
context.Background()
func Background() Context {
	return background
}

// but what is background? it's:
var (
	background = new(emptyCtx)
	todo       = new(emptyCtx)
)
emptyCtxWithCancel()
// WithCancel returns a copy of parent with a new Done channel. The returned
// context's Done channel is closed when the returned cancel function is called
// or when the parent context's Done channel is closed, whichever happens first.
//
// Canceling this context releases resources associated with it, so code should
// call cancel as soon as the operations running in this Context complete.
func WithCancel(parent Context) (ctx Context, cancel CancelFunc) {
	c := newCancelCtx(parent)
	propagateCancel(parent, &c)
	return &c, func() { c.cancel(true, Canceled) }
}

// A cancelCtx can be canceled. When canceled, it also cancels any children
// that implement canceler.
type cancelCtx struct {
	Context

	mu       sync.Mutex            // protects following fields
	done     chan struct{}         // created lazily, closed by first cancel call
	children map[canceler]struct{} // set to nil by the first cancel call
	err      error                 // set to non-nil by the first cancel call
}
UseContextcancel
// cancel closes c.done, cancels each of c's children, and, if
// removeFromParent is true, removes c from its parent's children.
func (c *cancelCtx) cancel(removeFromParent bool, err error) {
	if err == nil {
		panic("context: internal error: missing cancel error")
	}
	c.mu.Lock()
	if c.err != nil {
		c.mu.Unlock()
		return // already canceled
	}
	c.err = err
	if c.done == nil {
		c.done = closedchan
	} else {
		close(c.done) // NOTE(jiajun): here it is :)
	}
	for child := range c.children {
		// NOTE: acquiring the child's lock while holding parent's lock.
		child.cancel(false, err)
	}
	c.children = nil
	c.mu.Unlock()

	if removeFromParent {
		removeChild(c.Context, c)
	}
}
close(c.done)UseContext

总结

这篇博客里我们看到了context是怎么实现的，读者如果有兴趣的话，可以看看Context中的传值和取值是怎么实现的，以及思考一下 是否有更好的实现方案。

更多文章