multithreading - When a goroutine blocks on I/O how does the scheduler identify that it has stopped blocking?

Question

From what I've read here, the golang scheduler will automatically determine if a goroutine is blocking on I/O, and will automatically switch to processing others goroutines on a thread that isn't blocked.

What I'm wondering is how the scheduler then figures out that that goroutine has stopped blocking on I/O.

Does it just do some kind of polling every so often to check if it's still blocking? Is there some kind of background thread running that checks the status of all goroutines?

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For example, if you were to do an HTTP GET request inside a goroutine that took 5s to get a response, it would block while waiting for the response, and the scheduler would switch to processing another goroutine. Now given that, when the server returns a response, how does the scheduler understand that the response has arrived, and it's time to go back to the goroutine that made the GET so that it can process the result of the GET?

Answer 1

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