How Does the Go Scheduler Resume Goroutines After I/O-Bound Operations?

How Go Scheduler Detects Resumed Goroutines After I/O

In Go, the scheduler handles blocked goroutines by selecting other goroutines for execution on unbound threads. However, it's crucial to understand how the scheduler identifies when a goroutine has ceased to be blocked on I/O.

The Runtime's Role in Syscalls

Unlike conventional programming languages where syscalls are made directly, Go employs a managed runtime environment. When a syscall is invoked, it's intercepted by the runtime, which mediates its execution on behalf of the goroutine. This approach enables the runtime to utilize non-blocking syscalls and retain control over the goroutine's status.

Non-Blocking Syscalls and Callbacks

The runtime leverages non-blocking syscalls, which instruct the kernel to initiate operations without blocking the thread. Instead, the kernel notifies the runtime once the operation is complete. The runtime then resumes the goroutine responsible for the syscall.

Example: HTTP GET Request

Consider an HTTP GET request made within a goroutine. The runtime initiates a non-blocking syscall to make the request. While the request is in progress, the scheduler switches to other goroutines. Upon receiving a response from the server, the kernel signals the runtime, which in turn resumes the goroutine that made the request.

Therefore, the Go scheduler is able to detect resumed goroutines after I/O by virtue of the runtime's managed syscall mechanism and its ability to control the execution of goroutines.

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