How to handle the buffered channel properly in Golang?

Question

I have a channel which stores received data, I want to process it when one of following conditions is met:
1, the channel reaches its capacity.
2, the timer is fired since last process.

I saw the post Golang - How to know a buffered channel is full

Update:

I inspired from that post and OneOfOne's advice, here is the play :

package main

import (
    "fmt"
    "math/rand"
    "time"
)

var c chan int
var timer *time.Timer

const (
    capacity     = 5
    timerDration = 3
)

func main() {
    c = make(chan int, capacity)
    timer = time.NewTimer(time.Second * timerDration)
    go checkTimer()
    go sendRecords("A")
    go sendRecords("B")
    go sendRecords("C")

    time.Sleep(time.Second * 20)
}

func sendRecords(name string) {
    for i := 0; i < 20; i++ {
        fmt.Println(name+" sending record....", i)
        sendOneRecord(i)
        interval := time.Duration(rand.Intn(500))
        time.Sleep(time.Millisecond * interval)
    }
}

func sendOneRecord(record int) {
    select {
    case c <- record:
    default:
        fmt.Println("channel is full !!!")
        process()
        c <- record
        timer.Reset(time.Second * timerDration)
    }
}

func checkTimer() {
    for {
        select {
        case <-timer.C:
            fmt.Println("3s timer ----------")
            process()
            timer.Reset(time.Second * timerDration)
        }
    }
}

func process() {
    for i := 0; i < capacity; i++ {
        fmt.Println("process......", <-c)
    }
}

This seems to work fine, but I have a concern, I want to block the channel writing from other goroutine when process() is called, is the code above capable to do so? Or should I add a mutex at the beginning of the process method?

Any elegant solution?

Answer 1

No, select is the only way to do it:

func (t *T) Send(v *Val) {
    select {
    case t.ch <- v:
    default:
        // handle v directly
    }
}

Answer 2

As was mentioned by @OneOfOne, select is really the only way to check if a channel is full.

If you are using the channel to effect batch processing, you could always create an unbuffered channel and have a goroutine pull items and append to a slice.

When the slice reaches a specific size, process the items.

Here's an example on play

package main

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

const BATCH_SIZE = 10

func batchProcessor(ch <-chan int) {
    batch := make([]int, 0, BATCH_SIZE)
    for i := range ch {
        batch = append(batch, i)
        if len(batch) == BATCH_SIZE {
            fmt.Println("Process batch:", batch)
            time.Sleep(time.Second)
            batch = batch[:0] // trim back to zero size
        }
    }
    fmt.Println("Process last batch:", batch)
}
func main() {
    var wg sync.WaitGroup
    ch := make(chan int)
    wg.Add(1)
    go func() {
        batchProcessor(ch)
        wg.Done()
    }()
    fmt.Println("Submitting tasks")
    for i := 0; i < 55; i++ {
        ch <- i
    }
    close(ch)
    wg.Wait()
}