Because of that missing runtime for scheduling and evaluating IO-ful things, tools like superfunctions are necessary.
In other words: IO monads are only as useful as the thing that evaluates them; Python doesn't have a built-in way to do that, so people have to make code that looks "upward" to determine what kind of IO behavior (blocking/nonblocking/concurrent/lazy/etc.) is needed.
There’s no reason a python-like language couldn’t have deeper semantics for async, and language level implementation.
You seem to know a lot about PL. Could you elaborate on that reason and on the maintenance burden of a preemptive runtime?
Monad-agnostic functions are exactly looking upwards to allow the calling context to determine behaviour.
If I want to (say) probe a dozen URLs for liveness in parallel, or write data to/from thousands of client sockets from my webserver, doing that with threads--especially free-threaded Python threads, which are still quite lock-happy inside the interpreter, GIL or not--has a very quickly-noticeable performance and resource cost.
Async/await's primary utility is that of a capable utility interface for making I/O concurrent (and parallel as well, in many cases), regardless of whether threads are in use.
Hell, even golang multiplexes concurrent goroutines' threads onto concurrent IO schedulers behind the scenes, as does Java's NIO, Erlang/BEAM, and many many similar systems.
I like working in Java because you can use the same threading primitives for both and have systems that work well in both IO-dominated and CPU-dominated regimes which sometimes happen in the same application under different conditions.
Personally there are enough details to work out that we might be up to Python 3.24 when you can really count on all your dependncies to be thread safe. One of the reasons Java has been successful is the extreme xenophobia (not to mention painful JNI) which meant we re-implemented stuff to be thread-safe in pure Java as opposed to sucking in a lot of C/C++ stuff which will never be thread safe.
People are still hung up on this 1999 article
https://www.kegel.com/c10k.html
but hardware has moved on. I'm typing this on a machine with 16 CPU cores and I'm more worried about leaving easy parallelism on the table (even when it only gets say a 40% overall speedup) more than I am in 5% overhead from OS threads. I've seen so much buggy code that tries to get it correct with select() and io_uring() and all that but doesn't quite. Google has to handle enough questions to care, and you probably don't. If you worry about these things (right or wrong) Java has your back with virtual threads.
But there are a lot of common problems where the overhead of threads shows up a lot earlier in the scaling process than you'd think. Probing sets of ~100 URLs to see which are live? Even in a fast, well-threaded language, the overhead of creating/probing/shutting down all those threads adds up to noticeable latency very quickly. Creating lingering threadpools requires pre-planning available thread-parallelism and scheduling (say) concurrent web requests' workloads onto those shared pools with care. Compared to saying "I know these concurrent computations are 99.9% slow IO-wait-bound while probing URLs, let the event loop's epoll take care of it", that's a hassle--and just as hard to get right as manually messing about with select/poll/epoll multiplexers.
You're right that there are a lot of buggy IO multiplexer implementations out there; that kind of stuff is best farmed out to a battle-hardened event loop, ideally one that's distributed with your language runtime. But such systems aren't "google scale only", they're needful in a lot of places for ordinary programs' work--whether or not they're ever coded manually or interacted with directly in those programs.
If you don't often see problems like the hypothetical URL liveness checker, consider the main socket read/write components of a webserver harness: do you really want to spin up a thread as soon as bytes arrive on a socket to be read/written? Or would you rather allocate a precious request-handler thread (or process, or whatever) only after an efficient IO-multiplexed event loop has parsed enough of a request off of the socket to begin handling it? Plenty of popular webservers take both approaches. The ones that prefer evented I/O for their core request flow are less vulnerable to SlowLoris.
There are more benefits to async/await concurrency (and costs, too), including cancellation/timeout semantics, prioritization, and more, but even without getting into those, near-automatic IO multiplexing is pretty huge.
The real problem in web crawlers and such is supporting "one-thread per target server and limited request rate per target server" which is devilishly hard to do with whatever framework you're using on a single machine and even harder when you have a distributed crawler. I think some the rage people have about AI crawlers is the high cost of bandwidth out of AWS, but some of it has to be that the AI crawlers don't even seem to try anymore.
[1] https://mastodon.social/@UP8/114887102728039235 really!
With Python's asyncio, yes, you can read from many client sockets in a core, but you really can't do much work with them in the core, otherwise even the IO will slow down. It is not future-proof at all.
And sure, Golang's much better than a cooperative concurrency system at giving work out to multiple cores once the IO finishes, no argument there.
But again . . . async/await in Python (and JavaScript, Java NIO, and many more) is not about using multiple cores for computations; it's about efficiently making IO concurrent (and, if possible, parallel) for unpredictably "IO-wide" workloads, of which there are many.
The IO (read, write) doesn't need to finish, just the poll call. That's a very different thing in terms of core utilization, and while it's technically a serialization point, it's not the only serialization point in Go's architecture; it falls out from Go having a single, global run queue, requiring all (idle) threads to serialize on dequeueing tasks.
But thank you for pointing that out. TIL, there's a single epoll queue for the whole Go process: https://github.com/golang/go/issues/65064
~my_superfunction()
#> so, it's just usual function!
There's a way to work around that but...
> The fact is that this mode uses a special trick with a reference counter, a special mechanism inside the interpreter that cleans up memory. When there is no reference to an object, the interpreter deletes it, and you can link your callback to this process. It is inside such a callback that the contents of your function are actually executed. This imposes some restrictions on you:
> - You cannot use the return values from this function in any way...
> - Exceptions will not work normally inside this function...
Ummm...I'm maybe not the target audience for this library. But...no. Just no.
For async to be useful you've got to be accessing the network or a pipe or sleep so you have some context, you might as well encapsulate this context in an object and if you're doing that the object is going to look like
class base_class:
@maybe_async
def api_call(parameters)
... transform the parameters for an http call ...
response = maybe_await(self.http_call(**http_parameters))
... transform the response to a result ...
return result
since you can use basically the same http client for both sides. One way to do it is write code like the sample I showed and use
https://docs.python.org/3/library/ast.html
to scan the tree and either remove the maybe_await() or replace it with an await accordingly. You could either do this transformation when the application boots or have some code that builds both sync and async packages and packs the code up in PyPi. There are lots of ways to do it.
That's basically the genesis of the idea of maybe-async. I've cooled tremendously on the idea, personally, because it turns out that a lot of code has rather different designs throughout the entire stack if you're relying on sync I/O versus async I/O, and this isn't all that useful in practice.
Does this not add further function colors - that of a transfunction, tiddle superfunction and non-tilde superfunction? Now every time you call one from another you need to use both the context managers and know what variant you are calling.
asgiref provides the simple wrappers sync_to_async() and async_to_aync(). Easy to understand and to slowly transition. Caveat is the performance impact if overused.
synchronicity uses a different approach - write 100% async code and expose both a sync and async interface. async def foo() becomes def foo() and async def foo.aio().
https://github.com/django/asgiref https://github.com/modal-labs/synchronicity
The decorator would be a lot more useful if it abstracted all that away automagically. I/O bound stuff could be async and everything else would be normal.
Because nomen est omen, everything done now will just result in a growing pile of complexity. (see also the "class" misnomer for types), until someone looks again, and give the proper name - or operator - to the concept.
I imagine a future where we have a single operator on a line, like a "." which says: do everything from the last point to here parallel or async - however you want, in any order you want - but here is the point where everything has to be done ("joined"), before proceeding.
That's just semantic nitpicking. Everybody knows what async/sync means. The term is established for a very long time.
pomponchik•6mo ago
nine_k•6mo ago
Having separate sync / async versions that look like the same function is a great way to introduce subtle bugs.
[1]: https://kristoff.it/blog/zig-new-async-io/