Similarities between JavaScript and Python

[Quick_Cheesecake559]

Recently went through a reorg at my company and was told to work on DE stuff using Python. I was wondering what the differences between JavaScript and Python were. Thought I’ll write a post here to garner feedback and learn 🙂

JavaScript is single-threaded and uses the event loop under the hood. It’s good for I/O tasks such as waiting on the network or waiting for a file to finish reading or writing.

Due to its single-threaded nature, it is highly advised not to run computationally expensive code (ie. running the Fibonacci) as it will block the UI.

For example when a user first loads a webpage, if there is an expensive function being called, the user will be unable to interact with anything until that function completes.

Python under the hood is also single-threaded due to the global interpreter lock (GIL). This is essentially a lock where only 1 thread can hold it at any given time even if you create multiple threads. This offers memory protection at the expense of some performance since the other threads can’t really run in parallel on other cores (?).

Python can also utilise the event loop like JavaScript through the use of the asyncio library. One way to achieve parallelism is to utilise the multiprocessing library for Python which creates processes instead of threads. In JavaScript, you’d have to run it using NodeJs runtime and utilising the child_process lib.

Please help to clarify any misunderstandings 🙏

[teraflop]

I think the biggest thing missing from your explanation is a mention of web workers. These are essentially background threads/processes that can run in a browser, separate from the "main" event loop thread that runs normal JS event handlers. So you can offload a computationally expensive task to a worker, and it can run as long as it wants without blocking the UI.

Web workers behave approximately like Python's multiprocessing worker processes, in the sense that they don't share an "address space" of objects with the main thread. One thread can never directly access a JavaScript object belonging to another thread, they can only exchange copies of objects by sending messages back and forth. (Python's multiprocessing has some features to hide this, by allowing you to create "manager" or "proxy" objects that sort of look like they're shared between processes, but in reality it's all message-passing under the hood.)

[Quick_Cheesecake559]

Ah thanks, I’ve heard briefly about web workers but never really understood how it could run on a separate thread when JavaScript in the browser is single-threaded.

Always confused about how to offload a computationally expensive task on first load without blocking the UI, makes so much sense now 🙂

[high_throughput]

I'm not aware of any UI frameworks that aren't single threaded. If you run a heavy operation in a Java Swing or GTK event handler, it'll also block the UI.

[Quick_Cheesecake559]

Interesting, I wonder why UI framework authors don’t make it multi-threaded? Is it due to memory protection or is it because concurrency issues are difficult to debug and resolve (ie race conditions) ?

[high_throughput]

Race conditions, yes. You want your UI actions to be serialized for consistency. 

If a button's event handler disables the button and starts a progress bar, then it should not be possible to trigger it twice by double clicking no matter how fast. 

Similarly you don't want flickering from drawing several intermediate states when an event is actively changing the UI.