add context-examples

Author: bigwhite

context-examples/with_cancel/cancelctx_map.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+// 直接使用parent cancelCtx
+func f1(ctx context.Context) {
+	go func() {
+		select {
+		case <-ctx.Done():
+			fmt.Println("goroutine created by f1 exit")
+		}
+	}()
+}
+
+// 基于parent cancelCtx创建新的cancelCtx
+func f2(ctx context.Context) {
+	ctx1, _ := context.WithCancel(ctx)
+	go func() {
+		select {
+		case <-ctx1.Done():
+			fmt.Println("goroutine created by f2 exit")
+		}
+	}()
+}
+
+// 使用基于parent cancelCtx创建的valueCtx
+func f3(ctx context.Context) {
+	ctx1 := context.WithValue(ctx, "key3", "value3")
+	go func() {
+		select {
+		case <-ctx1.Done():
+			fmt.Println("goroutine created by f3 exit")
+		}
+	}()
+}
+
+// 基于parent cancelCtx创建的valueCtx之上创建cancelCtx
+func f4(ctx context.Context) {
+	ctx1 := context.WithValue(ctx, "key4", "value4")
+	ctx2, _ := context.WithCancel(ctx1)
+	go func() {
+		select {
+		case <-ctx2.Done():
+			fmt.Println("goroutine created by f4 exit")
+		}
+	}()
+}
+
+func main() {
+	valueCtx := context.WithValue(context.Background(), "key0", "value0")
+	cancelCtx, cf := context.WithCancel(valueCtx)
+	f1(cancelCtx)
+	f2(cancelCtx)
+	f3(cancelCtx)
+	f4(cancelCtx)
+
+	time.Sleep(3 * time.Second)
+	fmt.Println("cancel all by main")
+	cf()
+	time.Sleep(10 * time.Second) // wait for log output
+}

context-examples/with_cancel/custom_cancelctx.go

@@ -0,0 +1,57 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"runtime"
+	"time"
+)
+
+func f1(ctx context.Context) {
+	ctx1, _ := context.WithCancel(ctx)
+	go func() {
+		select {
+		case <-ctx1.Done():
+			fmt.Println("goroutine created by f1 exit")
+		}
+	}()
+}
+
+type myCancelCtx struct {
+	context.Context
+	done chan struct{}
+	err  error
+}
+
+func (ctx *myCancelCtx) Done() <-chan struct{} {
+	return ctx.done
+}
+
+func (ctx *myCancelCtx) Err() error {
+	return ctx.err
+}
+
+func WithMyCancelCtx(parent context.Context) (context.Context, context.CancelFunc) {
+	var myCtx = &myCancelCtx{
+		Context: parent,
+		done:    make(chan struct{}),
+	}
+
+	return myCtx, func() {
+		myCtx.done <- struct{}{}
+		myCtx.err = context.Canceled
+	}
+}
+
+func main() {
+	valueCtx := context.WithValue(context.Background(), "key0", "value0")
+	fmt.Println("before f1:", runtime.NumGoroutine())
+
+	myCtx, mycf := WithMyCancelCtx(valueCtx)
+	f1(myCtx)
+	fmt.Println("after f1:", runtime.NumGoroutine())
+
+	time.Sleep(3 * time.Second)
+	mycf()
+	time.Sleep(10 * time.Second) // wait for log output
+}

context-examples/with_value/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"context"
+	"fmt"
+)
+
+func f3(ctx context.Context, req any) {
+	fmt.Println(ctx.Value("key0"))
+	fmt.Println(ctx.Value("key1"))
+	fmt.Println(ctx.Value("key2"))
+}
+
+func f2(ctx context.Context, req any) {
+	ctx2 := context.WithValue(ctx, "key2", "value2")
+	f3(ctx2, req)
+}
+
+func f1(ctx context.Context, req any) {
+	ctx1 := context.WithValue(ctx, "key1", "value1")
+	f2(ctx1, req)
+}
+
+func handle(ctx context.Context, req any) {
+	ctx0 := context.WithValue(ctx, "key0", "value0")
+	f1(ctx0, req)
+}
+
+func main() {
+	rootCtx := context.Background()
+	handle(rootCtx, "hello")
+}