[rrishi]

I am not too deeply experienced with Python so forgive my ignorance.

But I am curious to understand why you were not able to utilize the concurrency tools provided in Python.

A quick google search gave me these relevant resources

1. An intro to threading in Python (https://realpython.com/intro-to-python-threading/#conclusion...)

2. Speed Up Your Python Program With Concurrency (https://realpython.com/python-concurrency/)

3. Async IO in Python: A Complete Walkthrough (https://realpython.com/async-io-python/)

Forgive me for my naivety. This topic has been bothering me for quite a while.

Several people complain about the lack of threading in Python but I run into plenty of blogs and books on concurrency in Python.

Clearly there is a lack in my understanding of things.

[Jtsummers]

Re (3): asyncio does not give you a boost for CPU bound tasks. It's a single-threaded, cooperative multi-tasking system that can (if you're IO bound) give you a performance boost.

[hughesjj]

Ehhh I mean you're not wrong, but I wouldn't say you're fully right either.

You can absolutely send stuff to a thread pool executor or process pool executor and then never await the returned value/never have it "return until interrupted, but the issues with shared memory (or really, the lack thereof in comparison to ex C) are still present to my understanding.

Then again, I mean you can always spin up a sqllite server or something on the same machine, but that's stupid heavy and more of a workaround than a solution. Super excited for nogil.

https://docs.python.org/3/library/concurrent.futures.html#co...

[mypalmike]

Not sure why you mention "thread pool executor", which of course does not get you concurrency due to the gil.

[xcv123]

Pedantic nerd nitpick: it gives you concurrency but not parallelism. (Concurrent threads can be time sliced on one core)

[IshKebab]

It was clear from the context that he meant concurrently running not concurrently in progress. I wish nerds would give up on this parallelism/concurrency pedantry or at least choose some new nomenclature that didn't conflict so massively with the English meaning of "concurrent".

I mean it's not even right. Most parallel/concurrent pedants would consider multithreaded code to be "parallel" even if it is running on a single core.

I think the best thing is to talk about threads, because then you can distinguish e.g. OS threads and hardware threads.

[xcv123]

> I mean it's not even right. Most parallel/concurrent pedants would consider multithreaded code to be "parallel" even if it is running on a single core.

If you're using these as technical terms which have specific technical definitions, then concurrency and parallelism are distinct but related concepts, and parallel computing means executing code simultaneously on separate execution units, not time sliced on a single core. So yes I am actually right about this. Parallel computing is defined this way in CS and it's not a matter of opinion.

[da39a3ee]

> I mean it's not even right. Most parallel/concurrent pedants would consider multithreaded code to be "parallel" even if it is running on a single core.

Hm, I think running on a single core is the exact definition of what the "pedants" say is not parallel. If all you have is one core then you can't achieve parallelism under their definition.

I think the terminology is pretty well established now. But I do agree with you that it's a bad choice of words and that it's annoying, intelligent even, for people to pick a particular unintuitive definition and then go around brow-beating people for not using/understanding their definition.

[wmwmwm]

You can throw python threads at it, but if each request traverses the big old datastructure using python code and serialises a result then you’re stuck with only one live thread at a time (due to the GIL). In Java it’s so much easier especially if the datastructure is read only or is updated periodically in an atomic fashion. Every attempt to do something like this in python has led me to having to abandon nice pythonic datastructures, fiddle around with shared memory binary formats, before sighing and reaching for java! Especially annoying if the service makes use of handy libraries like numpy/pandas/scipy etc!

[teraflop]

The whole point of the GIL is that even if you use Python's threading or asyncio, you don't get any benefits from scaling beyond a single CPU core, because all of your threads (or coroutines) are competing for a single lock. They run "concurrently", but not actually in parallel. The pages you linked explain this in more detail.

In theory, multiprocessing could allow you to distribute the workload, but in a situation like OP describes -- just serving API requests based on a data structure -- the overhead of dispatching requests would likely be bigger than the cost of just handling the request in the first place. And your main server process is still a bottleneck for actually parsing the incoming requests and sending responses. So you're unlikely to see a significant benefit.

[aardvark179]

Threading in Python is fine if your threads are io bound or spend their time in a C extension which releases the GIL, if you are bound then the GIL means effectively one thread can run at a time and you gain no advantage from multiple threads.

[indeedmug]

I had this misunderstanding for a long time until I saw Go explain the difference: https://go.dev/blog/waza-talk

The confusion here is parallelism vs concurrency. Parallelism is executing multiple tasks at once and concurrency is the composition of multiple tasks.

For example, imagine there is a woodshop with multiple people and there is only one hammer. The people would be working on their projects such as a chair, a table, etc. Everyone needs to use the hammer to continue their project.

If someone needed a hammer, they would take the single hammer and use it. There are still other projects going on but everyone else would have to wait until the hammer is free. This is concurrency but not parallelism.

If there are multiple hammers, then multiple people could use the hammer at the same time and their project continues. This is parallelism and concurrency.

The hammer here is the CPU and the multiple projects are threads. When you have Python concurrency, you are sharing the hammer across different projects, but it's still one hammer. This is useful for dealing with blocking I/O but not computing bottlenecks.

Let's say that one of the projects needs wood from another place. There is no point in this project to hold on to the hammer when waiting for wood. This is what those Python concurrency libraries are solving for. In real life, you have tasks waiting on other services such as getting customer info from a database. You don't want the task to be wasting the CPU cycles doing nothing, so we can pass the CPU to another task.

But this doesn't mean that we are using more of the CPU. We are still stuck with a single core. If we have a compute bottleneck such as calculating a lot of numbers, then the concurrency libraries don't help.

You might be wondering why Python only allows for a single hammer/CPU core. It's because it's very hard to get parallelism properly working, you can end up with your program stalling easily if you don't do it correctly. The underlying data structures of Python were never designed with that in mind because it was meant to be a scripting language where performance wasn't key. Python grew massive and people started to apply Python to areas where performance was key. It's amazing that Python got so far even with GIL IMO.

As an aside, you might read about "multiprocessing" Python where you can use multiple CPU cores. This is true but there are heavy overhead costs to this. This is like building brand-new workshops with single hammers to handle more projects. This post would get even longer if I explained what is a "process" but to put it shortly, it is how the OS, such as Windows or Linux, manages tasks. There is a lot of overhead with it because it is meant to work with all sorts of different programs written in different languages.