Why Do Goroutines Behave Differently on Go Playground vs. Local Machine?

Discrepancies between Go Playground and Go on Your Machine

When comparing the behavior of goroutines in Go on the Go Playground and on your local machine, you may encounter discrepancies. To clarify the underlying reasons, let's delve into your specific example.

On the Go Playground, with GOMAXPROCS initially set to 1, the code you provided is expected to produce a "Process took too long" error. This is because the goroutine created within the other() function executes an infinite loop, preventing the main goroutine from continuing and receiving data from the done channel.

However, on your local machine, the GOMAXPROCS value is likely set to a higher number (e.g., the number of CPU cores available). This allows multiple goroutines to run concurrently. In your case, the main goroutine receives data from the done channel while the other goroutine runs the infinite loop in parallel. Once the data is received, the main goroutine proceeds and terminates the program, irrespective of the other goroutine still running.

This non-deterministic behavior is inherent to the Go memory model. The order of execution of goroutines is not guaranteed, unless explicit synchronization mechanisms are employed.

Explanation:

On the Go Playground, GOMAXPROCS is set to 1. This means that only one goroutine can run at a time. In your code, the main goroutine executes the main() function and creates a second goroutine that executes the other() function. The main goroutine then waits on the done channel, which is blocked.

Since only one goroutine can run at a time, the scheduler chooses to continue running the other() function. This function sends a value on the done channel, making both the current (other()) and the main goroutine runnable. However, the scheduler continues to run other(), since GOMAXPROCS=1.

Other() then launches another goroutine executing an endless loop. The scheduler chooses to execute this goroutine, which takes forever to reach a blocked state. As a result, the main() function is not continued and the program runs indefinitely, prompting the "Process took too long" error on the Go Playground.

Locally, GOMAXPROCS is likely greater than 1. This allows multiple goroutines to run concurrently. Once other() sends data to the done channel, the scheduler can switch to the main goroutine, which proceeds to finish and terminate the program. Even if other goroutines are still running, the program will exit when the main goroutine terminates.

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