In the previous article
 we saw how sysmon steps in every 10ms to call netpoll(0) on behalf of busy Ps, making sure network I/O doesn’t stall when the scheduler is too busy to poll on its own. We glossed over what that network poller actually is. Today we’re fixing that.
Go’s networking story is one of its most quietly impressive tricks. You write code that looks blocking — conn.Read(buf), conn.Write(buf), listener.Accept() — and it reads exactly like the classic threaded servers from decades ago. But under the hood, no OS thread is actually blocked on those calls. Behind the scenes the runtime is driving epoll on Linux, kqueue on BSD/macOS, and I/O Completion Ports on Windows, parking and waking goroutines as readiness events arrive. The synchronous API you see is a comfortable illusion — and the machinery that maintains it is the network poller, or netpoller for short.

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A deep dive into Go's network poller (netpoller), explaining how the runtime provides a blocking-looking API while using non-blocking I/O under the hood. Covers the pollDesc data structure, the three-state parking protocol (pdNil/pdWait/goroutine pointer) that prevents lost wakeups, platform-specific kernel interfaces (epoll on Linux, kqueue on BSD/macOS, IOCP on Windows), deadline handling via runtime timers, stale event filtering with generation counters, and how the scheduler integrates netpoll to avoid dedicated poller threads. The result: a million concurrent connections on a handful of OS threads, with code that still reads like simple blocking calls.

Internals for Interns

The Problem: Blocking API, Non-Blocking Reality

Parking: Falling Asleep Without Missing the Bell

Deadlines: Giving Up Without Asking the Kernel

Stale Notifications: Making Sure the Bell Belongs to You