context finished but not practice

context/context-why.go

@@ -0,0 +1,43 @@
+package main
+
+import (
+	"fmt"
+	"sync"
+	"time"
+)
+
+var wg sync.WaitGroup
+
+//var notify bool
+
+//var exitChan chan bool = make(chan bool, 1)
+
+// why context
+
+func f() {
+	defer wg.Done()
+	//loop:
+	for {
+		fmt.Println("hello world")
+		time.Sleep(time.Millisecond * 500)
+		//if notify {
+		//	break
+		//} //变量
+		//select {
+		//case <-exitChan:
+		//	break loop
+		//default:
+		//} //channel 版本
+	}
+
+}
+
+func main() {
+	wg.Add(1)
+	go f()
+	time.Sleep(time.Second * 3)
+	//如何通知goroutine退出？
+	//exitChan <- true
+	wg.Wait()
+
+}

context/context-withcancel.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+func gen(ctx context.Context) <-chan int {
+	dst := make(chan int)
+	n := 1
+	go func() {
+		for {
+			select {
+			case <-ctx.Done():
+				return // return结束该goroutine，防止泄露
+			case dst <- n:
+				n++
+			}
+		}
+	}()
+
+	return dst
+}
+func main() {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel() // 当我们取完需要的整数后调用cancel
+
+	for n := range gen(ctx) {
+		fmt.Println(n)
+		if n == 5 {
+			break
+		}
+	}
+}

context/context-withdeadline.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+func main() {
+	d := time.Now().Add(2000 * time.Millisecond)
+	ctx, cancel := context.WithDeadline(context.Background(), d)
+
+	// 尽管ctx会过期，但在任何情况下调用它的cancel函数都是很好的实践。
+	// 如果不这样做，可能会使上下文及其父类存活的时间超过必要的时间。
+	defer cancel()
+
+	select {
+	case <-time.After(1 * time.Second):
+		fmt.Println("overslept")
+	case <-ctx.Done():
+		fmt.Println(ctx.Err())
+	}
+}

context/context-withtimeout.go

@@ -0,0 +1,39 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"time"
+)
+
+// context.WithTimeout
+
+var Wg sync.WaitGroup
+
+func worker(ctx context.Context) {
+LOOP:
+	for {
+		fmt.Println("db connecting ...")
+		time.Sleep(time.Millisecond * 10) // 假设正常连接数据库耗时10毫秒
+		select {
+		case <-ctx.Done(): // 50毫秒后自动调用
+			break LOOP
+		default:
+		}
+	}
+	fmt.Println("worker done!")
+	Wg.Done()
+}
+
+func main() {
+	// 设置一个50毫秒的超时
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*50)
+	Wg.Add(1)
+	go worker(ctx)
+	time.Sleep(time.Second * 5)
+	cancel() // 通知子goroutine结束
+	Wg.Wait()
+	fmt.Println("over")
+}

context/context-withvalue.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+
+	"time"
+)
+
+// context.WithValue
+
+type TraceCode string
+
+var wait sync.WaitGroup
+
+func workerProc(ctx context.Context) {
+	key := TraceCode("TRACE_CODE")
+	traceCode, ok := ctx.Value(key).(string) // 在子goroutine中获取trace code
+	if !ok {
+		fmt.Println("invalid trace code")
+	}
+LOOP:
+	for {
+		fmt.Printf("worker, trace code:%s\n", traceCode)
+		time.Sleep(time.Millisecond * 10) // 假设正常连接数据库耗时10毫秒
+		select {
+		case <-ctx.Done(): // 50毫秒后自动调用
+			break LOOP
+		default:
+		}
+	}
+	fmt.Println("worker done!")
+	wait.Done()
+}
+
+func main() {
+	// 设置一个50毫秒的超时
+	ctx, cancel := context.WithTimeout(context.Background(), time.Millisecond*50)
+	// 在系统的入口中设置trace code传递给后续启动的goroutine实现日志数据聚合
+	ctx = context.WithValue(ctx, TraceCode("TRACE_CODE"), "12512312234")
+	wait.Add(1)
+	go workerProc(ctx)
+	time.Sleep(time.Second * 5)
+	cancel() // 通知子goroutine结束
+	wait.Wait()
+	fmt.Println("over")
+}

context/context.go

@@ -0,0 +1,52 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+)
+
+var WG sync.WaitGroup
+
+func f1(ctx context.Context) {
+	defer WG.Done()
+	go f2(ctx)
+loop:
+	for {
+		fmt.Println("hello world")
+		time.Sleep(time.Millisecond * 500)
+		select {
+		case <-ctx.Done():
+			break loop
+		default:
+
+		}
+	}
+
+}
+func f2(ctx context.Context) {
+	defer WG.Done()
+loop:
+	for {
+		fmt.Println("hello wangao")
+		time.Sleep(time.Millisecond * 500)
+		select {
+		case <-ctx.Done():
+			break loop
+		default:
+
+		}
+	}
+}
+
+func main() {
+	ctx, cancel := context.WithCancel(context.Background())
+	WG.Add(1)
+	go f1(ctx)
+	time.Sleep(time.Second * 3)
+	//如何通知goroutine退出？
+	cancel()
+	WG.Wait()
+
+}

context/context.log

@@ -0,0 +1 @@
+如何优雅的控制子goroutine退出？

leetcode/reverseList.go

@@ -0,0 +1,47 @@
+package main
+
+import "fmt"
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func reverseList(head *ListNode) *ListNode {
+	var pre *ListNode
+	cur := head
+	for cur != nil {
+		tmp := cur.Next //暂存初始方向
+		cur.Next = pre  //改变链表方向
+		pre = cur       //移动指针
+		cur = tmp       //移动指针2
+	}
+	return pre
+}
+
+func main() {
+	head := &ListNode{
+		Val: 1,
+		Next: &ListNode{
+			Val: 2,
+			Next: &ListNode{
+				Val: 3,
+				Next: &ListNode{
+					Val: 4,
+					Next: &ListNode{
+						Val:  5,
+						Next: nil,
+					},
+				},
+			},
+		},
+	}
+	fmt.Printf("%#v\n", head)
+	ret := reverseList(head) //反转之后的头节点
+	fmt.Printf("%#v\n", ret)
+	for ret != nil {
+		fmt.Print(ret.Val, "->")
+		ret = ret.Next //指针移动，直到链表的尾部
+	}
+
+}