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A pure Python stack makes introspection possible, and additionally you can maintain a tree structure of stacks rather than a single stack. (The root of this tree is the C stack that starts off the first Python function/method.) The big win with the tree structure is, as Chris pointed out, is that you
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It is false in the sense that
Stackless of course has continuations in their full sense, that is you can take a snapshot of a running program and start this several times, concurrently. It is not directly supported any longer, but running tasklets may be pickled. It is up to the user to load a stored
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Well this is true in the sense that the article includes old information. Continuations were the target of the first implementations, later on I changed to the less powerful but easier to understand taskletmodel, which is some kind of one-shot continuations. Actually, this appears to be the only kind
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But as it stands, now in 2018, CPython has achieved a lot of what
Stackless had. It took 15 years, and they adopted a way more complicated way do squeeze all concurrency into generators, using "yield from" or the modern syntactic sugar, but it is far enough to say that Python 3.5 and up have solved
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Stackless isn't experimental now that's it's in 3 major commercial releases. The point about how much more easily conccurent processes are run as the major influence for choosing this product over regular Python needs expounding. A programmer would be better suited than I. Maybe look at Second
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What they have still not used is the feature of pickling program state. With
Stackless, you can capture a running program, stop it and resume it later, or even on a different machine. That part of Stackless might still be a feature that could be adopted by CPython - of course with quite different
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In ordinary C-based Python, there is a commingling of the call stack for Python with the call stack for C. What I mean is that for one Python function or method to call another, it drops down into the C world and comes back up. State information connecting the caller and the callee lives on the C
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Essentially correct. "Stackless" just means that it uses a tree structure instead of stack(s) to keep track of the state of different threads. This allows cooperative-multitasking microthreads, and a few other interesting features. It's sort of a niche platform, because "micro" doesn't mean free.
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This sounds somewhat funny. Where do the numbers come from? 20KB for what? Well, if you hit a special case and switch tasklets from inside a C extension, then you get more or less C stack crap to be saved, but the general case is much different: A few bytes, fust for the Python frames and a tiny
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And about the tasklets: I thought of a one-shot continuation because the continuation inside the tasklet is not restartable, but a different one after suspend/resume. But I think that makes no sense, it is actually a coroutine. I should probably be more aware of the literature.
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Is it faster? More efficient? More secure? More suited for specific tasks where ordinary Python doesn't cut it? "It's Python, without the stack" isn't very informative. If this be clarified in the article, it'd be highly appreciated.
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Isn't it crucial for invoked continuations to refer to the same environment as they did when they were captured? I think most of the things continuations are used for are impossible if that isn't the case.
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Look, I fancy myself as a computer scientist even when I'm really a plain ordinary Sunday programmer who knows a lot of tiny little details but fails to understand the big picture at times. I know what a
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And about the tasklets: are they really one-shot continuations, or coroutines? In other words, can you invoke previously-captured continuations of a tasklet, or just suspend/resume the current tasklet?
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I think that talking to the author of the following article and reusing the bulk of it where it doesn't specifically apply to game programming would allow a more extensive entry here:
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Each task eats up something like 20KB, and the scheduler isn't very fast, so it starts adding up to a major performance hit after a couple thousand tasks (original research). --
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That is the big difference: Stackless can modify the execution state, easily, because it is not blocking structures on the stack, but has it available as a data structure.
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tasklet from disk multiple times. This is almost like full continuations, despite the fact that the variables are not shared between the instances.
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Agreed that this is needed--as far as I can tell the number 1 (only?) reason to use
Stackless over regular Python is because it supports
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posted by
Christian Tismer to the Stackless Mailing list on March, 2004. Newer versions have light weight threads called tasklets. --
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I wish to mention that this artical is several years out of date. Stackless no longer supports continuations, as mentioned in a
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tasklet structure, that's it. And why is the scheduler slow? It is at least 80 times faster than switching real threads.
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is, but this article fails to answer a rather big question why I wanted to read the article in first place:
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If no one objects, I'll try to write some examples that show
Stackless's strengths versus vanilla Python.
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Yes, you are right, and I stand corrected. The cloning of tasklets cannot be compared with continuations.
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on
Knowledge (XXG). If you would like to participate, please visit the project page, where you can join
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This is correct except for the stack introspection, which CPython supports without difficulty. (See
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get fast light threads. You can see these and some other applications at
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Christian Tismer, creator of
Stackless Python -- 15:02, 18 August 2005
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