Does `time.Sleep` Really Block Goroutines?

Does time.Sleep Block Goroutines?

In Go, a common misconception is that time.Sleep blocks goroutines, leading to concerns about excessive thread creation.

Understanding Go Scheduler

Go uses a Multiple Producer, Single Consumer (MPG) scheduler, where a limited number of threads called M share jobs from a queue serviced by Ps (worker goroutines). When an M is idle, it takes a job from the queue and executes it.

Does time.Sleep Really Block Goroutines?

Yes, time.Sleep blocks goroutines in the sense that it prevents further execution of the current goroutine during the sleep period.

Why Limited Thread Creation When Using time.Sleep?

Despite the blocking nature of time.Sleep, the Go scheduler may not spawn new threads due to two reasons:

1. Optimization: The scheduler can detect that the goroutine is not performing any work during the sleep period and does not need an active M.
2. Resource Constraints: It may not be possible to create additional threads due to limitations imposed by the operating system or runtime environment.

Difference in Thread Creation Between Examples

Your first example, where goroutines sleep for an extended time, uses a fixed number of threads because the scheduler can determine that no additional processing is needed during the sleep period. In contrast, your second example, which involves concurrent IO operations, requires more threads since each goroutine actively performs IO tasks.

When to Worry About Thread Creation

Generally, Go's scheduler handles thread creation efficiently. However, in rare cases, such as when you intentionally create an excessive number of goroutines that spend most of their time in blocking I/O operations, you may encounter issues with excessive thread creation.

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