Event Loop Internals
Coroutines are scheduled on the event loop as Tasks, which are managed in a task queue. The event loop continuously picks ready coroutines from this queue and executes them.
When a coroutine hits await on an I/O operation, the event loop:
- Suspends the coroutine
- Moves it to the waiting queue
- Registers the I/O operation with an I/O multiplexer
- Linux: epoll. MacOS & BSD: kqueue. Windows: IOCP
This allows the event loop to continue handling other ready coroutines.
Once the I/O operation completes, the OS notifies the event loop via the I/O multiplexer. The event loop then:
- Moves the corresponding coroutine from the waiting queue back to the ready queue
- Resumes execution of the coroutine from right after the
awaitstatement