lotusirous / go-concurrency-patterns Goto Github PK

why does one worker complete eight tasks?

Hello, I have tested your ring buffer, and the output consisted of 5 values:

2024/04/03 07:39:49 5
2024/04/03 07:39:49 6
2024/04/03 07:39:49 7
2024/04/03 07:39:49 8
2024/04/03 07:39:49 9

However, the buffer for the channel was set to 4. Therefore, I find this response somewhat unclear.

This is a bug surely? Another routine could write between these two calls, and then this write would block.

A safer approach would be to drop the current write AND one from the ring buffer. This would ensure that no code ever blocks, but you are still guaranteed new data (which IMO is a big use-case for ring buffers).

This would ensure no back-pressure. It would make starvation technically possible very rarely by some complex timing and workload patterns if you have too many writers for the size of the ring buffer, but this is trivial to avoid by sizing the ring buffer appropriately.

So as long as your ring buffer isn't too small, I think it would behave more like what people would expect.

We always think timeout as the time that one service has on response. In this case, timeout 's meaning should be ** we don't receive any message from c channel for 5 seconds.

so maybe the right code is :

timeout := time.After(5 * time.Second)
for {
       select {
       case s := <-c:
               fmt.Println(s)
               timeout = time.After(5 * time.Second) // update timeout time
       case <-timeout:
               fmt.Println("channel has no response for 5 seconds")
               return
       }
}

the origin code seems that you want to receive from every channel for same time, like linux cfs scheduler. so maybe in that case we should use ticker

package main

import (
        "fmt"
        "time"
)

func boring(id int) <-chan string {
        c := make(chan string)
        go func() {
                 c <- "" // skip the first time
                for i := 0; ; i++ {
                        c <- fmt.Sprintf("%d, %s", id, time.Now().Format("2006-01-02 15:04:05"))
                        time.Sleep(1 * time.Second)
                }
        }()
        return c
}

func main() {
        timeout := time.NewTicker(5 * time.Second)
        c1 := boring(1)
        c2 := boring(2)
        jobchannels := []<-chan string{c1, c2}
        i := 0
        for {
                select {
                case s := <-jobchannels[i]:
                        fmt.Println(s)
                case <-timeout.C:
                        fmt.Printf("%d has talk for 5 secs\n", i+1)
                        i = (i + 1) % len(jobchannels)
                }
        }
}

and it's output is

1, 2021-03-17 11:27:03
1, 2021-03-17 11:27:04
1, 2021-03-17 11:27:05
1, 2021-03-17 11:27:06
1, 2021-03-17 11:27:07
1 has talk for 5 secs

2, 2021-03-17 11:27:08
2, 2021-03-17 11:27:09
2, 2021-03-17 11:27:10
2, 2021-03-17 11:27:11
2, 2021-03-17 11:27:12
2 has talk for 5 secs
1, 2021-03-17 11:27:08
1, 2021-03-17 11:27:14
1, 2021-03-17 11:27:15
1, 2021-03-17 11:27:16
....

The main in item 14 https://github.com/lotusirous/go-concurrency-patterns/blob/main/14-adv-subscription/main.go is not implemented.