Context Switch

Due to Synchronous System Calls

When Goroutine makes synchronous system call, Go scheduler bring new OS thread from thread pool.
Gorotine which made the system call will still be attached to old thread.
Other Goroutines in LRQ are scheduled for execution on new OS thread.
Once system call returns, Goroutine is moved back to run queue on logical procesor P and old thread is put to sleep.

File descriptor is set to non-blocking mode.
If file descriptor is not ready, for I/O operation, system call does not block, but reutrns an error.
Asynchronous IO increases the application complexity.
Setup event loops using callbacks functions.

Netpoller to convert asynchronous system call to blocking system call.
When a goroutine makes a asynchronous system call, and file descriptor is not ready, goroutine is parked at netpoller os thread.
netpoller uses interface provided by OS to do polling on file descriptors
- kqueue (MacOS)
- epoll (Linux)
- iocp (Windows)
Netpoller gets notification from OS, when file descriptor is ready for I/O operation.
Netpoller notifies goroutine to retry I/O operation.
Complexity of managing asynchronous system call is moved from Application to Go runtime, which manages it efficiently.

Go use netpoller to handle asynchronous system call.
netpoller uses interface provided by OS to do polling on file descriptors and notifies to the goroutine to try I/O operation when it ready.
Application complexity of managing asynchronous system call is moved to Go runtime, which manages it efficiently.