sjansen/mecha

package main

import (
    "context"
    "flag"
    "fmt"
    "math/rand"
    "os"
    "strconv"
    "sync"
    "time"

    "github.com/sjansen/mecha/internal/subprocess"
)

var id int

func init() {
    flag.IntVar(&id, "as-test-child", 0, "")
}

func main() {
    flag.Parse()
    if id > 0 {
        makeSomeNoise()
    } else {
        startChildren()
    }
}

func makeSomeNoise() {
    pid := os.Getpid()
    fmt.Printf("Started (id=%-2d pid=%d)\n", id, pid)

    rand := rand.New(rand.NewSource(int64(id)))
    n := rand.Intn(12) + 3
    time.Sleep(time.Duration(n) * time.Second)

    n = rand.Intn(7)
    if n < 5 {
        fmt.Printf("Stopped (id=%-2d pid=%d)\n", id, pid)
        os.Exit(0)
    } else {
        fmt.Printf("Crashed (id=%-2d pid=%d)\n", id, pid)
        os.Exit(1)
    }

}

func spawn(ctx context.Context, i int) int {
    id := strconv.Itoa(i)
    p, err := subprocess.New(ctx, os.Args[0], "--as-test-child", id).
        CaptureStdoutLines().
        CaptureStderrLines().
        Start()
    if err != nil {
        fmt.Fprintln(os.Stderr, err)
        return -1
    }

    label := fmt.Sprintf("%3s:", id)
    for {
        select {
        case line := <-p.Stdout:
            if line != "" {
                fmt.Fprintln(os.Stdout, label, line)
            }
        case line := <-p.Stderr:
            if line != "" {
                fmt.Fprintln(os.Stderr, label, line)
            }
        case status := <-p.Status:
            return status.Code
        }
    }
}

func startChildren() {
    var wg sync.WaitGroup

    start := 10
    var crashed, stopped, restarted int
    ctx, cancel := context.WithTimeout(context.Background(), 16*time.Second)
    defer cancel()
    for i := 1; i <= start; i++ {
        wg.Add(1)
        go func(i int) {
            defer wg.Done()
            for {
                if rc := spawn(ctx, i); rc == 0 {
                    stopped++
                } else {
                    crashed++
                }
                select {
                case <-ctx.Done():
                    return
                default:
                    restarted++
                }
            }

        }(i)
    }

    wg.Wait()
    fmt.Println(
        "started:", start,
        "| restarted:", restarted,
        "| crashed:", crashed,
        "| stopped:", stopped,
    )
}