Re: [go-nuts] An old problem: lack of priority select cases

[Robert Engels]

That's inherently racy - since between when the runtime determines the channel is OK for writing, another routine can close the channel before the write is attempted - so "priorities" won't help.

-----Original Message-----
From: T L
Sent: Aug 28, 2019 11:06 AM
To: golang-nuts
Subject: [go-nuts] An old problem: lack of priority select cases

The old thread: https://groups.google.com/forum/#!topic/golang-nuts/ZrVIhHCrR9o

Go channels are flexible, but in practice, I often encountered some situations in which channel are hard to use.

Given an example:

import "math/rand"

type Producer struct {
    data   chan int
    closed chan struct{}
}

func NewProducer() *Producer {
    p := &Producer {
        data:   make(chan int),
        closed: make(chan struct{}),
    }
   
    go p.run()
   
    return p
}

func (p *Produce) Stream() chan int {
    return p.data
}

func (p *Producer) run() {
    for {
        // If non-blocking cases are selected by their appearance order,
        // then the following slect block is a perfect use.
        select {
        case(0) <-p.closed: return
        case p.data <- rand.Int():
        }
    }
}

func (p *Produce) Clsoe() {
    close(p.closed)
    close(p.data)
}

func main() {
    p := NewProducer()
    for n := p.Stream() {
        // use n ...
    }
}

If the first case in the select block in the above example has a higher priority than the second one,

then coding will be much happier for the use cases like the above one.

In short, the above use case requires:

* for receivers, data streaming end is notified by the close of a channel.
* for senders, data will never be sent to closed channel.

But, as Go 1 doesn't support priority select cases, it is much tedious to implement the code

satisfying the above listed requirements. The final implementation is often very ugly and inefficient.

Does anyone else also experience the pain?

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