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Unladen Swallow is dead (groups.google.com)
171 points by ot on Dec 10, 2010 | hide | past | web | favorite | 57 comments

No, it's not dead, and I'm sad that this is sitting at the front page, because it's so misleading.

The fact is, it's stalled (https://www.google.com/buzz/bcannon/bZDN1jNZ3uC/Is-this-fina...) - http://www.python.org/dev/peps/pep-3146/ was accepted. This means that a branch was made with the intent of merging US into Py3k. Unfortunately, this proved to be a greater task then originally planned. Stalled != Dead.

To quote Collin: "Unladen Swallow is stalled because merging the code into the py3k-jit branch plain sucks: lots of new compatibility work to be done, lots of corners we had to un-cut, lots of drudge and suffering. It doesn't help that Google is full of far more interesting and influential projects."

So add in the fact that the resources Google had "assigned" to the project got moved/reassigned onto something else, and what you have is a very stalled project. Collin has stated that they hope(d) that other python-core devs would/will step up to help, but everyone is pretty tapped out as it is.

I'm as disappointed as anyone that it's stalled - given it's compatibility with C extensions, potential speedups and future potential, it has been one of the projects I've had the most hope for.

That said, PyPy is also coming along; when they hit 2.7 compatibility and they have drop-in replacement capability, the ecosystem will be very interesting. Competition in the interpreter space is good, and I feel that Unladen's aggressiveness helped spur/move PyPy along.

That said Unladen (in my mind) remains the CPython interpreter's best way of moving into the future. It still has the most promise for that code base.

jnoller, I may have indulged in catchiness at the expense of accuracy and I am sorry if the title is misleading.

I hoped that this thread would raise some discussion about the status of US, as, after a lot of publicity on project launch, there have not been many official statements from the team. I have followed the project since the beginning and saw the exponential decay of traffic in the mailing list and commits as the promised performance improvements seemed less achievable (but it has to be said that the US team contributed to LLVM a lot of useful code, like gdb debugging of JITted code).

So my question is: why is US relevant since it hasn't achieved any significant performance boost? Why should we believe in the "potential speedups and future potential" if there is no evidence that supports them?

I myself had done some experiments with implementing a python JIT with LLVM some time before US was launched and had the same results, 10-15% improvement on microbenchmarks at expense of huge memory increase and compilation times.(see https://groups.google.com/d/topic/unladen-swallow/bqf9TzWHht... )

It seems that the bottleneck is not in the interpreter loop, but in the CPython runtime API. I am afraid that, if the interpreter has to stick to CPython source compatibility, it cannot get rid of the overhead. But I would be very happy to be proven wrong.

When asked - on the mailing list, on google buzz, or anywhere else, Collin and Jeffery and others have been very open about its status. They've always dealt us (as the community) a fair hand about the status of the project, and the path moving forward.

Your indulgence in catchiness is annoying, as it will be echoed (and it already has been) all over the place with breathless drama "Look! It's Dead!" when, despite languishing, the code is still there, still functional, but starved of resources. The editorializing is frustrating, misleading and overall, I think harmful.

As for why it's still relevant: Easy, it's the only currently visible way of moving the CPython interpreter forward from an evolution standpoint. US does show a series of speedups, one thats useful for CPython. To quote:

"A JIT compiler is an extremely flexible tool, and we have by no means exhausted its full potential. Unladen Swallow maintains a list of yet-to-be-implemented performance optimizations [49] that the team has not yet had time to fully implement. Examples:" - http://www.python.org/dev/peps/pep-3146/

I would recommend: if you want to move anything forward, or help, rather than make posts like this, jump in on the http://svn.python.org/view/python/branches/py3k-jit/

Yes; part of the reason the current interpreter is limited is due to backwards compatibility, but I'd rather have a limited JIT with some performance gains then none at all.

The fundamental issue is that Jeffery, Collin and Reid - the founding three are "off in the woods" - and they're the only ones who understand the code enough to move it forward right now. PyPy's success(es) are orthogonal to the evolution of the CPython interpreter code base.

I am sorry this thread is turning into a flame... I would like to make clear that I am not questioning whether or not US is good thing to happen to CPython, just that it is now a project without maintainers (the post suggests that they will stop working on it after the py3k-jit merge) and without an active community. As you said it is a very complex piece of code and even if it is "still functional" it is definitely not ready, as the performance gains are not substantial.

I have nothing against calling it "stalled", but IMHO it is just an euphemism for "dead".

Also I don't understand why people at Google decided to stop investing on it, the cost of 3 full time engineers is nothing compared to the millions they would save with a more efficient python implementation, given their huge python infrastructures (App Engine, for example).

If this is a flame war, then it's a pretty tame one :)

As for Google's intentions, I've learned (as it has been explained to me time and time again) - never attribute smaller decisions to a larger strategy or "plan" of Google's. It probably not that they decided to stop investing in it, more than "something more interesting came up".

I do wish that we could have funded work on core/the interpreter. That would be nice.

"Look matey, I know a dead swallow when I see one, and I'm looking at one right now. The plumage don't enter into it. It's stone dead!"

Wrong bird and wrong python. (The latter is meant in both ways!)

This sort of thing is one of the reasons why I'm very careful in picking the pieces that make up the tools that I earn my living with.

Left right and center you're bombarded with 'use this', 'use that', but most of these projects end up not having much staying power and if you depend on them for the running of your business then sooner or later you might end up having to support them.

When I choose an open source component these are the things I like to see in the eco system around it before deciding to jump in (obviously not every project selected will have all of these, but more helps):

- multiple maintainers, active response to patches being sent in

- broad support, using open standards

- preferably a drop in replacement available

- lively community of people willing to help each other out

- two years track record with a good roadmap for future support

- people working on it because they like it, not because they get paid to (this one is probably very counter intuitive when you're looking at this problem from a business point of view, but it is my opinion that people working on something because they like it are automatically in for the long haul).

Every time I've been seduced by new, hot and sexy technology I've come to regret it sooner or later. Old, boring and solid seems to win the race every time.

Running a small shop means that the investment you make in a tool is one of the most important decisions you can make, the wrong decision could cost you a lot of time and/or cripple your company.

I hope that everybody using unladen swallow is able to easily transition to a replacement.

There is no need to transition from unladen swallow since almost nobody was using it. It was a fork of cpython, and the speed improvements were so negligeable that I doubt anyone sane would try to use this without mastering the - heavy - technology behind.

I was actually quite shocked when unladen swallow was somehow almost accepted for python 3.2 at some point, given how bad the performance results were: if you add C++ + llvm and all the new infrastructure/complexity it brings, you rather have good numbers, not something like 10 % speed improvements which was the order of magnitude last time I checked.

It did bring useful code to python, though: in terms of benchmark code, but also proving that speeding up python while keeping cpython compatibility (vs just python compat) is actually pretty hard (which was expected, but they confirm the suspicion).

> I was actually quite shocked when unladen swallow was somehow almost accepted for python 3.2 at some point, given how bad the performance results were

Memory is getting cheaper. I was looking forward the GIL removal (at first), but I'll be happy with any multi-threading improvement.

OTOH, when I really needed it, the multiprocessing module did the job nicely. And it also prevents some very hard to catch bugs.

Unladen has never intended to remove the GIL - their primary goal was to keep compatibility with C extensions without even recompiling IIRC (google seems to rely a lot on python extension around their infrastructure), and removing the GIL will break many, many extensions: the only known way to remove the GIL without cause a huge slow down is to remove reference counting, which C extensions rely on, and also most C extensions rely on the fact they don't need to be reentrant.

Removing the GIL was one of the explicit goals as originally conceived, but was dropped when it was realized how difficult it would be (source: http://code.google.com/p/unladen-swallow/wiki/ProjectPlan#Gl...).

I run most of my Python program on fairly low end boxes, so consuming 9MB per process vs 90 would be a pretty big deal. If you have RAM to burn, share :).

The rule is that next year, you'll be able to run twice as many processes as you do today for the same amount of server money.

And, besides that, Unladen Swallow would most probably take 18 or 27 MB per process on your scenario. 10x more memory seems weird.

In my use case, large data processing, I would prefer slower processing in exchange for lower memory requirements. The more ram it eats the sooner my processes have to hit disk.

Yes, I suppose you are right about the memory usage: http://www.python.org/dev/peps/pep-3146/#memory-usage. And of course Moore's law has been on target so far. However, next year I'll want to run more kinds of different processes, putting more projects on my servers and I'd rather conserve RAM as much as possible.

The PEP was/is accepted. The problem is all the resources with the knowledge to merge it have since been reassigned. It's still pending merge into py3k.

That's not entirely accurate, the PEP is about merging it in a new branch called py3k-jit. AFAIK there are no plans of merging it in the main, vanilla, py3k.

Look at the header - 3.3 the intention was to accept the PEP, do the merge, and then ask for final approval for merge into Py3k. The intention on both sides was to always merge it into vanilla Py3k.

Yes you are right, what I meant is that it will still need a "final approval", which I think will imply a more thorough discussion and a round of voting.

The "merge plan" section states that, before that, all the jit-related patches will be confined in the py3k-jit branch

And you're right; final approval won't come because well, it ain't done.

Agreed. I'm not waiting for another Java, either, When carelessly integrating a JIT there would be a big risk of long startup times and other memory-heavy behaviour.

Of course, there are also examples of JIT that seem more lightweight, such as the javascript JITs.

pypy has quicker start up than CPython and also has a JIT. They're working on interesting memory optimisations too.

No one was using Unladen Swallow jacquesm - it was an experimental fork of CPython.

My bad, I thought it was in production use as well. But in a way that does not really detract from the main point, just from this particular application of that point.

Isn't unladen swallow pretty much a JIT drop-in replacement for Python itself? If that is the case, it ticks almost all of the boxes such as."using open standards", "drop in placement available".

     I hope that everybody using unladen swallow is able to 
     easily transition to a replacement.
Like CPython? :-)


That's hardly a drop-in replacement. CPython is.

Actually, PyPy is already a drop-in replacement for many uses, and is getting closer to being a complete drop-in replacement all the time. For example, they have a source-compatible implementation of the CPython C API: http://morepypy.blogspot.com/2010/04/using-cpython-extension...

_sooner or later you might end up having to support them_

It seems ironic that this is often cited as a reason not to use an open source project. Isn't the selling point supposed to be that you can support it if you really need to?

That said, the pragmatic part of me would rather work on my problems instead of my tools.

Reading the thread, it seems there's still an intention to roll the JIT into py3k at some point, but the project devs don't have the time and the community doesn't seem to have the inclination to take over the work. I think calling it dead might be overstating things slightly.

Or, seeing as this is Python we're talking about: It's not dead, it's just resting.

The thing is, in two years the project was able to deliver only a very small, say 1.2x, speedup, with a noticeable increase of memory (sometimes 3x). Against Python 2.6. I wouldn't be surprised if Python 2.7 is actually faster on some tests. Is it really worth keeping working on it and merging?

Part of the reason Python 2.7 is faster on some benchmarks is because of the patches the unladen swallow team pushed upstream into core.

> It's not dead, it's just resting.

And doing what US already did is about equivalent to eating a cow.

With PyPy moving ahead so well, I wonder if there's much point to Unladen Swallow anymore. Weren't they always expecting to be a stopgap until PyPy was ready?

Last time I checked, PyPy wasn't compatible with modules written in C. That's a show stopper for many of us.

Can I use CPython extension modules?

Yes, but the feature is in alpha state and is available only on trunk (not in the 1.2 release). However, we'll only ever support well-behaving CPython extensions. Please consult PyPy developers on IRC or mailing list for explanations if your favorite module works and how you can help to make it happen in case it does not. We fully support ctypes-based extensions, however.


Wow! That's really cool!

Their working on it...


It's worthy to note that GIL is still there in pypy

Unladen Swallow looked very promising, came out with lots of excitement and news. It overannounced and underdelivered. I tend to prefer underannouncing and overdelivering...

If you never fail, you need harder things to do.

On the other hand, if you never publicly fail you may just be prudent. Or paranoid. Or depriving yourself of some beneficial pressure. But it's not quite as clear-cut as you make it seem.

IMHO, ambition is not publicity. Setting high ambitions doesn't mean make big announcements like "make python 5x faster" without any evidence that the approach is promising. OTOH the pypy guys, for example, have kept a much lower profile but much higher ambitions, like write a completely new compiler toolchain with a novel architecture and then implement python on top of it. I wouldn't say they didn't have "harder things to do".

> I tend to prefer underannouncing and overdelivering...

Yes, assuming that you hear about the project at all. Overannouncement is lying, but it does get you more publicity.

"I tend to prefer underannouncing and overdelivering..."

An example of this would be Mike Pall and his LuaJIT project.

Nice editorializing there. I suggest readers who care should read the entire thread, and be careful when they see future posts from "ot".

I read the entire thread and it seems to me that the project is dead (or not very far from it).

  Jeffrey and I have been pulled on to other projects of
  higher importance to Google. Unfortunately, no-one from
  the Python open-source community has been interested in
  picking up the merger work, and since none of the original
  team is still full-time on the project, it's moving very
  slowly. Finishing up the merger into the py3k-jit branch is
  a high priority for me this quarter, but what happens then
  is an open question."
When working on open source, especially something as complicated as this, you need at least one dedicated maintainer. Looks to me that they are trying to do the responsible thing and tie up any loose ends.

Are we reading the same page? I don't see anything saying it's dead. Perhaps out of focus, but there's still a plan to merge.

I don't either. This same thread gets posted on Reddit's /r/Python seemingly once every few weeks and everyone freaks out all over again.

It’s not dead, it’s just pining for the fjords.

Is there a wise one among us who could summarize the characteristics and status of the various Python interpreters us Python amateurs should be excited about?

Here is a comprehensive list of Python implementations: http://wiki.python.org/moin/PythonImplementations

Funny, I was just talking about them not being able to remove the GIL today while working through a tornado app.

I wonder what the future holds for pypy.

It's not dead, it's sleeping.

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