Why Do Goroutines on Go Playground and Local Machines Exhibit Behavioral Differences?

Discrepancies between Go Playground and the Local Machine

When running a code on the Go playground, developers may encounter discrepancies compared to running the same code on their local machines. This article explores the behavioral differences, particularly when dealing with goroutines and synchronization mechanisms.

Case Study: Code Behavior on Go Playground vs. Local Machine

Consider the following Go code:

<code class="go">package main

import (
    "fmt"
)

func other(done chan bool) {
    done <- true
    go func() {
        for {
            fmt.Println("Here")
        }
    }()
}

func main() {
    fmt.Println("Hello, playground")
    done := make(chan bool)
    go other(done)
    <-done
    fmt.Println("Finished.")
}

On the Go playground, this code produces an error: "Process took too long." This suggests that the goroutine created within the other function runs indefinitely.

However, running the same code on a local machine with multiple CPU cores (GOMAXPROCS > 1) yields the following output:

<code class="text">Hello, playground
Finished.</code>

This implies that the goroutine created within other terminates when the main goroutine finishes.

Explaining the Behavioral Gap

The different behavior between the Go playground and the local machine can be attributed to the number of processors available. On the Go playground, GOMAXPROCS defaults to 1, meaning only a single goroutine can run at a time. Therefore, in the above example, the endless goroutine created within other prevents the main goroutine from continuing.

In contrast, when running locally with multiple CPU cores, GOMAXPROCS defaults to the number of available cores, allowing multiple goroutines to run concurrently. Thus, the endless goroutine created within other does not block the main goroutine from exiting.

Conclusion

The behavior of goroutines in Go depends on the number of available processors (GOMAXPROCS). While the Go playground uses a default value of 1 which can lead to the perception of goroutines running indefinitely, running the same code on a local machine with multiple cores provides a different behavior where goroutines may terminate when the main goroutine finishes. This understanding helps developers avoid misunderstandings and ensures that their code behaves as expected in different environments.

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