Go语言并发编程基础上下文概念详解

package main
import "fmt"
func main() {
    dataCom := []string{"alex", "kyrie", "kobe"}
    go func(data []string) {
        // 模拟大量运算的死循环
    }(dataCom)
    // 其他代码正常执行
    fmt.Println("剩下的代码执行正常逻辑")
}

package main
import (
	"fmt"
	"time"
)
func main() {
	stopChannel := make(chan bool)
	dataCom := []string{"alex", "kyrie", "kobe"}
	go func(stopChannel chan bool) {
		go func(data []string) {
			// 大量的计算
		}(dataCom)
		for range time.After(2 * time.Second) {
			fmt.Println("此操作运行时间过长，取消中")
			stopChannel <- true
		}
	}(stopChannel)
	<-stopChannel
	// 其他代码正常执行
	fmt.Println("剩下的代码执行正常逻辑")
}

package main
import (
	"context"
	"fmt"
	"time"
)
func main() {
	ctx, cancel := context.WithTimeout(context.Background(), time.Second*2)
	defer cancel()
	dataCom := []string{"alex", "kyrie", "kobe"}
	go func() {
		go func(data []string) {
			// 大量的计算
		}(dataCom)
		for range time.After(2 * time.Second) {
			fmt.Println("此操作运行时间过长，取消中")
			cancel()
			return
		}
	}()
	select {
	case <-ctx.Done():
		fmt.Println("上下文被取消")
	}
}

type Context interface {
  Deadline() (deadline time.Time, ok bool)
  Done <-chan struct{}
  Err() error
  Value(key interface{}) interface{}
}

ctx, cancel := context.Background()

ctx, cancel := context.TODO()

type valueCtx struct {
    Context
    key, val interface{}
}

package main
import (
  "context"
  "fmt"
)
type contextKey string
func main() {
  var authToken contextKey = "auth_token"
  ctx := context.WithValue(context.Background(), authToken, "Hello123456")
  fmt.Println(ctx.Value(authToken))
}

package main
import (
  "context"
  "fmt"
  "math/rand"
  "time"
)
func main() {
  rand.Seed(time.Now().UnixNano())
  ctx, cancel := context.WithCancel(context.Background())
  defer cancel()
  for char := range randomCharGenerator(ctx) {
    generatedChar := string(char)
    fmt.Printf("%v\n", generatedChar)
    if generatedChar == "o" {
      break
    }
  }
}
func randomCharGenerator(ctx context.Context) <-chan int {
  char := make(chan int)
  seedChar := int('a')
  go func() {
    for {
      select {
      case <-ctx.Done():
        fmt.Printf("found %v", seedChar)
        return
      case char <- seedChar:
        seedChar = 'a' + rand.Intn(26)
      }
    }
  }()
  return char
}

package main
import (
    "bufio"
    "context"
    "fmt"
    "log"
    "os"
    "time"
)
func main() {
    // context with deadline after 2 millisecond
    ctx, cancel := context.WithDeadline(context.Background(), time.Now().Add(2*time.Millisecond))
    defer cancel()
    lineRead := make(chan string)
    var fileName = "sample-file.txt"
    file, err := os.Open(fileName)
    if err != nil {
        log.Fatalf("failed opening file: %s", err)
    }
    scanner := bufio.NewScanner(file)
    scanner.Split(bufio.ScanLines)
    // goroutine to read file line by line and passing to channel to print
    go func() {
        for scanner.Scan() {
            lineRead <- scanner.Text()
        }
        close(lineRead)
        file.Close()
    }()
outer:
    for {
        // printing file line by line until deadline is reached
        select {
        case <-ctx.Done():
            fmt.Println("process stopped. reason: ", ctx.Err())
            break outer
        case line := <-lineRead:
            fmt.Println(line)
        }
    }
}

func WithTimeout(parent Context, timeout time.Duration) (Context, CancelFunc) {
    // 当前时间+timeout就是deadline
    return WithDeadline(parent, time.Now().Add(timeout))
}

package main
import (
    "bufio"
    "context"
    "fmt"
    "log"
    "os"
    "time"
)
func main() {
    // context with deadline after 2 millisecond
    ctx, cancel := context.WithTimeout(context.Background(), 2*time.Millisecond)
    defer cancel()
    lineRead := make(chan string)
    var fileName = "sample-file.txt"
    file, err := os.Open(fileName)
    if err != nil {
        log.Fatalf("failed opening file: %s", err)
    }
    scanner := bufio.NewScanner(file)
    scanner.Split(bufio.ScanLines)
    // goroutine to read file line by line and passing to channel to print
    go func() {
        for scanner.Scan() {
            lineRead <- scanner.Text()
        }
        close(lineRead)
        file.Close()
    }()
outer:
    for {
        // printing file line by line until deadline is reached
        select {
        case <-ctx.Done():
            fmt.Println("process stopped. reason: ", ctx.Err())
            break outer
        case line := <-lineRead:
            fmt.Println(line)
        }
    }
}

package main
import (
    "context"
    "fmt"
    "time"
)
func main() {
    c := make(chan string)
    go func() {
        time.Sleep(1 * time.Second)
        c <- "one"
    }()
    ctx1 := context.Context(context.Background())
    ctx2, cancel2 := context.WithTimeout(ctx1, 2*time.Second)
    ctx3, cancel3 := context.WithTimeout(ctx2, 10*time.Second) // derives from ctx2
    ctx4, cancel4 := context.WithTimeout(ctx2, 3*time.Second)  // derives from ctx2
    ctx5, cancel5 := context.WithTimeout(ctx4, 5*time.Second)  // derives from ctx4
    cancel2()
    defer cancel3()
    defer cancel4()
    defer cancel5()
    select {
    case <-ctx3.Done():
        fmt.Println("ctx3 closed! error: ", ctx3.Err())
    case <-ctx4.Done():
        fmt.Println("ctx4 closed! error: ", ctx4.Err())
    case <-ctx5.Done():
        fmt.Println("ctx5 closed! error: ", ctx5.Err())
    case msg := <-c:
        fmt.Println("received", msg)
    }
}

package main
import (
    "context"
    "fmt"
)
func main() {
    ctx := context.Background()
    _, ok := ctx.Deadline()
    if !ok {
        fmt.Println("no dealine is set")
    }
    done := ctx.Done()
    if done == nil {
        fmt.Println("channel is nil")
    }
}

func DoSomething(ctx context.Context, arg Arg) error {
    // ... use ctx ...
}