Why does my Go program sometimes print the sum result before the \'display first message\'?

Go Concurrency and Channel Confusion: Understanding Goroutine Execution Order

In Go, concurrency is achieved through goroutines, lightweight threads that run concurrently within a single process. Channels provide a means of communicating between goroutines. However, understanding how goroutines and channels interact can be challenging, especially for beginners.

This article explores a common point of confusion related to goroutine execution order and channel communication. The example program provided:

<code class="go">package main

import "fmt"

func display(msg string, c chan bool) {
    fmt.Println("display first message:", msg)
    c <p>This program is expected to print "display first message: hello" as the first output, followed by the result of the sum computation. However, in some cases, the sum computation finishes before the display function sends data to the channel.</p>
<p><strong>Explanation:</strong></p>
<p>The scheduler in Go determines the order in which goroutines are executed. It is non-deterministic, meaning the execution order may vary depending on factors such as hardware and operating system. In this example:</p>
<ol>
<li>The main function creates two goroutines: display and sum.</li>
<li>The scheduler chooses to switch to the display goroutine first, which prints the "display first message" line.</li>
<li>The display goroutine is blocked when it tries to send data to the channel (c </li>
<li>The scheduler chooses to run the sum goroutine, which executes the computationally expensive loop.</li>
<li>Once the sum computation is finished, the sum goroutine sends data to the channel.</li>
<li>The main function receives the data from the channel and exits.</li>
</ol>
<p>However, it is also possible for the scheduler to execute the sum goroutine to completion before the display goroutine sends data to the channel. In this case, the output would be:</p>
<pre class="brush:php;toolbar:false">10000000000
display first message: hello

Solution:

To ensure that the display message is printed before the sum result, one can use a result channel to receive the first result and exit the program. The modified main function would be:

<code class="go">func main() {
    result := make(chan string)

    go display("hello", result)
    go sum(result)
    fmt.Println(</code>

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