Why Does `time.Sleep` Enable Concurrent Goroutine Execution in Go?

Time. Sleep and Goroutine Execution

In the provided code, the time.Sleep function plays a crucial role in enabling the execution of concurrent goroutines. When time.Sleep is commented out, the "world" goroutine never gets a chance to run.

The reason for this behavior lies in the non-preemptive nature of Go's goroutine scheduler. Unlike preemptive schedulers, the Go scheduler does not force currently running goroutines to yield control unless they voluntarily relinquish it. Without time.Sleep, the main goroutine monopolizes control, completing its say("hello") loop five times before returning. Since the main goroutine is responsible for the program's execution, the program exits immediately afterward, leaving no time for the "world" goroutine to execute.

With time.Sleep in place, the "world" goroutine can run while the main goroutine is waiting. When the main goroutine yields control to execute time.Sleep, the scheduler can switch to the "world" goroutine, allowing it to execute its first iteration before the main goroutine resumes. This alternation of control between goroutines ensures that both tasks can complete, resulting in the expected output with "world" and "hello" being printed to the screen interchangeably.

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