couldn't print numbers ordered with goroutine

[Taňryberdi Şyhmyradow]

Hello guys,

For the following lines, I wanted to print numbers in ordered, but couldn't. Could you please help me and explain the reason

Thanks in advance

```

numbers := []int{1, 2, 3, 4, 5}

// Create a buffered channel to handle multiple values
printed := make(chan int, len(numbers))

for _, n := range numbers {
    fmt.Println("Sending", n, "to the channel")
    go func() {
       printed <- n
    }() // Pass the value of n by copying it
}

// Receive all values from the channel in a loop
for i := 0; i < len(numbers); i++ {
    fmt.Println(<-printed)
}

```

--

Tanryberdi Shyhmyradov

[Justin Israel]

When you start a bunch of goroutines in a loop, there is no guarantee as to what order the scheduler will start each one. 

Thus you will see them delivered in different orders on each run. You have to decide on some form of synchronization. Maybe you choose to run a single goroutine worker that will loop over the source slice, and push the values into the channel in order. Or maybe you will keep using many goroutines but collect them all in the receiver, sort them after the last value is received, and then print them out. Or, maybe your receiver will have some kind of buffering where it collects values and only prints them when it has the next one in sequence. 

--

Tanryberdi Shyhmyradov

[Robert Solomon]

channels are not queues, as Justin said

[Dan Kortschak]

On Sat, 2024-04-20 at 18:55 -0700, Robert Solomon wrote:
> channels are not queues, as Justin said

They can be; buffered channels are queues.

From https://go.dev/ref/spec#Channel_types

> Channels act as first-in-first-out queues. For example, if one
> goroutine sends values on a channel and a second goroutine receives
> them, the values are received in the order sent.

[Justin Israel]

And really I wasn't even commenting on the nature of the channel. Only the scheduling of the goroutines. Buffered or not, they would still be random order right? 

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[Dan Kortschak]

On Sun, 2024-04-21 at 15:06 +1200, Justin Israel wrote:
> And really I wasn't even commenting on the nature of the channel.
> Only the scheduling of the goroutines. Buffered or not, they would
> still be random order right? 

Absolutely. Your answer was spot on. The issue is the ordering of the
goroutines' execution, not the behaviour of channels. I just wanted to
clarify the comment that responsed to that.