Does time.Sleep() Really Block Goroutines in Go?

Will time.Sleep Suspend a Goroutine?

Time.Sleep is often used in Go programs to pause execution for a specified duration. However, unlike some other programming languages, time.Sleep does not truly block goroutines.

MPG Model and Goroutine Scheduling

Go's runtime scheduler follows a model known as MPG (M: M's, P: P's, G: Goroutines). Each M (machine) runs P (processor) goroutines concurrently. If a goroutine enters a blocking state, its P dissociates from the M and finds an idle M or creates a new one if none is available.

Does time.Sleep Block Goroutines?

Yes, time.Sleep does indicate that a goroutine is in a blocking state. This means that the next statement cannot execute immediately, as the goroutine is momentarily unavailable.

Why Doesn't time.Sleep Create More Threads?

Despite the blocking nature of time.Sleep, the runtime scheduler may not create additional threads. This is because the scheduler aims to optimize performance and resource utilization. Therefore, if there are enough threads available to handle the non-sleeping goroutines, it does not allocate new threads for time.Sleeping goroutines.

Exception to the Rule

However, under exceptional circumstances, when there are a significant number of time.Sleeping goroutines, the scheduler may create additional threads to maintain responsiveness.

Difference between time.Sleep and Real IO

In the given example, the use of real IO resulted in a larger number of threads compared to using time.Sleep. This is because IO operations involve interacting with the operating system and external devices, which can introduce additional blocking points and require dedicated threads.

Conclusion

While time.Sleep indicates a blocking goroutine, it does not necessarily lead to the creation of new threads. The runtime scheduler optimizes thread allocation based on the available resources and the number of active goroutines. Developers should not be overly concerned about thread creation unless their programs are deliberately designed to simulate a pathological case of excessive thread usage.

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