CODEWITHSUNDEEP
goprocesssleepgoroutine
Kenenbek Arzymatov
Kenenbek Arzymatov

Reputation: 9119

Change the time of goroutine sleeping

In Go I can write such code for creating a gorouting that sleeps 5 sec.

func sleep(link chan interface{}){
    time.Sleep(5 * time.Second)
    fmt.Println("I've slept for 5 sec")
    link <- struct {}{}
}

func main() {
    var link = make(chan interface{})
    go sleep(link)
    time.Sleep(1 * time.Second)
    // here I want to change the remaining sleeping time of `sleep` goroutine to 0.5 sec
    <- link
}

What if in main function I change my mind and decide that the sleeper should sleep not 5 sec but 3. How can it done if goroutine already started to sleep (and sleeping, for example, for 1 sec)?

UPDATE

I mean is there something whereby I can manage that unique goroutine while it sleeps. Like giving commands to it about decreasing or increasing time of sleep:

func main() {
    // ...
    time.Sleep(1)
    something.ManageRemainingTime(10)
    time.Sleep(5)
    something.ManageRemainingTime(100)
    time.Sleep(8)
    something.ManageRemainingTime(0.5)
    // ...
}

Upvotes: 2

Views: 2204

Answers (3)

phemmer
phemmer

Reputation: 8797

One method is to use a timer. You can call Stop() on a timer, but this stops it without waking up whatever is waiting on it. So you then use Reset() to set it to a new value, specifically 0, which triggers it immediately.

Example:

package main

import (
    "fmt"
    "sync"
    "time"
)

func sleep(wg *sync.WaitGroup) *time.Timer {
    timer := time.NewTimer(5 * time.Second)
    go func() {
        tStart := time.Now()
        <-timer.C
        tStop := time.Now()
        fmt.Printf("Slept for %s\n", tStop.Sub(tStart))
        wg.Done()
    }()
    return timer
}

func main() {
    wg := sync.WaitGroup{}
    wg.Add(1)
    timer := sleep(&wg)
    if true {
        time.Sleep(3 * time.Second)
        if timer.Stop() {
            timer.Reset(0)
        }
    }
    wg.Wait()
}

https://play.golang.org/p/b3I65kAujR4

Change the if true { to if false { and you can see the Slept for ... change.

Upvotes: 2

phemmer
phemmer

Reputation: 8797

One method is to use a context object. Specifically one created with WithTimeout.

The context object provides a way of sending a "cancel" signal to a worker. In this case your worker is not really doing anything, but still fits the paradigm.

Example would be:

package main

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

func sleep(ctx context.Context, wg *sync.WaitGroup) {
    sctx, _ := context.WithTimeout(ctx, 5*time.Second)
    tStart := time.Now()
    <-sctx.Done() // will sit here until the timeout or cancelled
    tStop := time.Now()
    fmt.Printf("Slept for %s\n", tStop.Sub(tStart))
    wg.Done()
}

func main() {
    ctx, cancelFunc := context.WithCancel(context.Background())
    wg := sync.WaitGroup{}
    wg.Add(1)
    go sleep(ctx, &wg)

    if true {
        time.Sleep(3 * time.Second)
        cancelFunc()
    }
    wg.Wait()
}

https://play.golang.org/p/2Krx4PsxFKL

Change the if true { to if false { and you can see the Slept for ... change.

Upvotes: 3

dave
dave

Reputation: 64657

If you just need a way to "wakeup" a sleeping goroutine, you could use sync.Once to ensure your function only gets called once, and then return a channel so you can set a sooner "trigger time", so something this:

func sleep(callback func(), seconds int) chan int {
    once := sync.Once{}
    wakeup := make(chan int)
    go func() {
        for sleep := range wakeup {
            go func() {
                time.Sleep(time.Duration(sleep) * time.Second)
                once.Do(callback)
            }()
        }
    }()
    wakeup <- seconds
    return wakeup
}


func main() {
        wg := sync.WaitGroup{}
        wg.Add(1)
        t := time.Now()
        wakeup := sleep(func() {
            fmt.Println("Hello, playground")
            wg.Done()
        }, 5)
        wakeup <- 2
        wg.Wait()
        fmt.Println(time.Since(t))
}

https://play.golang.org/p/BRNtaBPKpLW

Upvotes: 3

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