Async Rust: From Futures To Production Part1 chapter2 - "Output, poll(), Context, Waker" diagram requires more detail #49
Description
The diagram simplifies the interplay between Executor and Reactor by lumping reactor with Resource(I/O) and Operating System.
While it'd be easier to understand for those who got to learn async rust for the first time, combining those three seem quite off.
I like to suggest the following diagram if it is not too complex
sequenceDiagram
participant E as Executor
participant F as Future (Task)
participant OS as Operating System<br/>(e.g., epoll/kqueue)
participant R as Reactor (Runtime)
E->>F: Calls poll(cx)
Note right of F: Future attempts operation
F->>OS: Syscall (e.g., read TCP socket #4)
OS-->>F: Returns Error: (Not Ready)
F->>R: Registers: (Waker)
F-->>E: Returns Poll::Pending
Note left of E: Task is moved out<br/>of run queue
E->>E: (Executor runs other tasks OR sleeps)
R->>OS: epoll_wait() / Polls OS for events
Note right of OS: (Sometime Later) New data arrives
OS-->>R: Wakes Reactor: data is NOW READABLE
Note over R: OS NOTIFIES REACTOR FIRST
R->>R: Reactor finds Waker
R->>E: Calls Waker::wake()
Note right of E: Task is pushed back<br/>to Executor's run queue
E->>F: Calls poll(cx) again
Note right of F: Future attempts operation again
F->>OS: Syscall (e.g., read TCP socket #4)
OS-->>F: Success: Returns Data Buffer
F-->>E: Returns Poll::Ready(Data)