Try It Yourself - SyntaxStudy Editor

HTML / CSS / JS

package main

import (
    "context"
    "fmt"
    "time"
)

func doWork(ctx context.Context, id int) error {
    select {
    case <-time.After(200 * time.Millisecond):
        fmt.Printf("worker %d finished
", id)
        return nil
    case <-ctx.Done():
        fmt.Printf("worker %d cancelled: %v
", id, ctx.Err())
        return ctx.Err()
    }
}

func fetchData(ctx context.Context, url string) (string, error) {
    // simulate a slow network request
    select {
    case <-time.After(500 * time.Millisecond):
        return "data from " + url, nil
    case <-ctx.Done():
        return "", fmt.Errorf("fetch %s: %w", url, ctx.Err())
    }
}

func main() {
    // WithCancel — manual cancellation
    ctx, cancel := context.WithCancel(context.Background())
    go func() {
        time.Sleep(100 * time.Millisecond)
        cancel() // cancel after 100ms
    }()
    doWork(ctx, 1)

// WithTimeout — automatic cancellation
    ctx2, cancel2 := context.WithTimeout(context.Background(), 300*time.Millisecond)
    defer cancel2()
    data, err := fetchData(ctx2, "https://example.com")
    if err != nil {
        fmt.Println("error:", err)
    } else {
        fmt.Println("received:", data)
    }
}