How async/await works in Python (2021)

https://tenthousandmeters.com/blog/python-behind-the-scenes-12-how-asyncawait-works-in-python/

by sebg • 1 year ago

61 7 1 year ago

quentinp• 1 year ago

While it stays at the Python level, https://github.com/AndreLouisCaron/a-tale-of-event-loops really helped me to understand how asyncio and Trio are implemented. I had no idea how sleeps worked before reading that post.

incomingpain• 1 year ago

Page didnt load for me.

https://realpython.com/async-io-python/

Multiprocessing all the way!

emmelaich• 1 year ago

(2021)

Good article!

punnerud2• 1 year ago

A more simplified version:

Synchronous code is like a single-lane road where cars (tasks) must travel one after another in perfect sequence. If one car stops for gas (waiting for I/O), every car behind it must stop too. While orderly and predictable, this creates massive traffic jams as tasks wait unnecessarily for others to complete before they can proceed.

Pure asynchronous code (with callbacks) is like dispatching multiple cars onto independent routes with no coordination. Cars move freely without waiting for each other, but they arrive at unpredictable times and following their progress becomes chaotic. It's efficient but creates a complex tangle of paths that becomes hard to maintain.

Async/await combines the best of both approaches with a multi-lane highway system. Cars follow clear, synchronous-looking routes (making code readable), but only wait at strategic "await" exit ramps when truly necessary. When a car needs data, it signals with "await", pulls off the highway temporarily, and other cars continue flowing past. Once its operation completes, it merges back into traffic and continues. This gives you the logical simplicity of synchronous code with the performance benefits of asynchronous execution - cars only wait at crossroads when they must, maximizing throughput while maintaining order.

The genius of async/await is that it lets developers write code that looks sequential while the runtime handles all the complex traffic management under the hood.

explodes• 1 year ago

Excellent write up. I appreciate the level of details here showing the history from the days of old, before async/await were even keywords.

bilsbie• 1 year ago

How does the GIL come into play here?

punnerud2• 1 year ago

GIL is like a "red-cap" on the head for the CPU-core running the task, so you would not be able to run true Async without GIL. Have to hand the "red-cap" back, for the next task.

Instead of using a global lock ("red-cap"), Python objects have introduced a specialized reference counting system that distinguishes between "local" references (owned by a single thread) and "shared" references (accessed by multiple threads).

In that way enabling to remove GIL in the long run, now starting with making it optional.

How async/await works in Python (2021)

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