When Do Goroutines Yield in Go: Synchronous vs. Asynchronous Preemption?

When Can Goroutines Yield in Go Programs?

Goroutines, the lightweight threads of Go, are crucial for concurrency. Understanding when they yield control is essential for optimizing code performance.

Traditional Preemption Points

Previously, goroutines only yielded at specific points, including:

• System calls that blocked execution
• Function calls (to check if the stack needs to grow)

Asynchronous Preemption (Go 1.14 )

Version 1.14 of Go introduced asynchronous preemption, meaning goroutines can now yield control almost anywhere. This reduces the risk of deadlocks and delays.

Preemption Points in Your Example

The example code provided in the question does not include function calls or blocking syscalls. However, the output still shows interleaving of messages, indicating that goroutines are yielding.

Possible Reasons for Preemption

• Asynchronous Preemption: The goroutines are yielding unpredictably due to asynchronous preemption.
• Garbage Collection: The use of strings in the output array can trigger garbage collection, which involves locks and scheduling switches.

Conclusion

In Go programs, goroutines can now yield control asynchronously at almost any point. This is an improvement from earlier versions that required specific preemption points. However, it's important to be aware of the potential impact of garbage collection and other factors that can influence goroutine scheduling.

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