Skip to content

Async runtime (executor and reactor)

Category: Scheduling · Status: stub · Lessons: chapter 06, Async (planned)

One line: The library that drives async tasks: an executor that polls the tasks that can make progress, and a reactor that wakes them when the I/O they wait for is ready.

Also called: executor, reactor, tokio, asyncio event loop.

How it connects

flowchart LR
  n_async_runtime["Async runtime (executor and reactor)"]
  n_event_loop["Event loop"]
  n_io_multiplexing["I/O multiplexing"]
  n_polling["Polling"]
  n_work_stealing["Work stealing"]
  n_async_runtime -->|uses| n_event_loop
  n_async_runtime -->|uses| n_io_multiplexing
  n_async_runtime -->|uses| n_polling
  n_async_runtime -->|uses| n_work_stealing
  classDef center stroke-width:3px
  class n_async_runtime center
  classDef outside stroke-dasharray: 4 3
  class n_event_loop,n_io_multiplexing,n_polling,n_work_stealing outside

In each language
Rust Not in the standard library: Tokio ↗, whose #[tokio::main] starts one, is the common choice
Python asyncio.run ↗ runs a coroutine in an event loop that it manages, and returns the result
Kotlin runBlocking ↗ bridges regular blocking code to suspending code, blocking its thread until the coroutine completes

Where to read more