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* 4179 - experiment: rip out memory reclamationKartik K. Agaram2018-01-031-180/+30
| | | | | | | | | | | | | | | | | | | | | I have a plan for a way to avoid use-after-free errors without all the overheads of maintaining refcounts. Has the nice side-effect of requiring manual memory management. The Mu way is to leak memory by default and build tools to help decide when and where to expend effort plugging memory leaks. Arguably programs should be distributed with summaries of their resource use characteristics. Eliminating refcount maintenance reduces time to run tests by 30% for `mu edit`: this commit parent mu test: 3.9s 4.5s mu test edit: 2:38 3:48 Open questions: - making reclamation easier; some sort of support for destructors - reclaiming local scopes (which are allocated on the heap) - should we support automatically reclaiming allocations inside them?
* 4104Kartik K. Agaram2017-11-031-5/+5
| | | | | Stop hardcoding Max_depth everywhere; we had a default value for a reason but then we forgot all about it.
* 3707Kartik K. Agaram2016-12-121-2/+1
| | | | | | | | | | | | | | | | | | Be more disciplined about tagging 2 different concepts in the codebase: a) Use the phrase "later layers" to highlight places where a layer doesn't have the simplest possible self-contained implementation. b) Use the word "hook" to point out functions that exist purely to provide waypoints for extension by future layers. Since both these only make sense in the pre-tangled representation of the codebase, using '//:' and '#:' comments to get them stripped out of tangled output. (Though '#:' comments still make it to tangled output at the moment. Let's see if we use it enough to be worth supporting. Scenarios are pretty unreadable in tangled output anyway.)
* 3651Kartik K. Agaram2016-11-081-0/+22
| | | | | | I was under the impression that I only needed static array lengths for container members, but these are *payload* types for allocations. So we need to compute the size of a dynamic array.
* 3645Kartik K. Agaram2016-11-071-1/+1
| | | | | | Extract a helper to compute the element type of an array. As a side effect, the hack for disambiguating array:address:number and array:number:3 is now in just one place.
* 3522Kartik K. Agaram2016-10-191-3/+3
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* 3381Kartik K. Agaram2016-09-171-3/+3
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* 3380Kartik K. Agaram2016-09-171-43/+43
| | | | | One more place we were missing expanding type abbreviations: inside container definitions.
* 3309Kartik K. Agaram2016-09-091-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Rip out everything to fix one failing unit test (commit 3290; type abbreviations). This commit does several things at once that I couldn't come up with a clean way to unpack: A. It moves to a new representation for type trees without changing the actual definition of the `type_tree` struct. B. It adds unit tests for our type metadata precomputation, so that errors there show up early and in a simpler setting rather than dying when we try to load Mu code. C. It fixes a bug, guarding against infinite loops when precomputing metadata for recursive shape-shifting containers. To do this it uses a dumb way of comparing type_trees, comparing their string representations instead. That is likely incredibly inefficient. Perhaps due to C, this commit has made Mu incredibly slow. Running all tests for the core and the edit/ app now takes 6.5 minutes rather than 3.5 minutes. == more notes and details I've been struggling for the past week now to back out of a bad design decision, a premature optimization from the early days: storing atoms directly in the 'value' slot of a cons cell rather than creating a special 'atom' cons cell and storing it on the 'left' slot. In other words, if a cons cell looks like this: o / | \ left val right ..then the type_tree (a b c) used to look like this (before this commit): o | \ a o | \ b o | \ c null ..rather than like this 'classic' approach to s-expressions which never mixes val and right (which is what we now have): o / \ o o | / \ a o o | / \ b o null | c The old approach made several operations more complicated, most recently the act of replacing a (possibly atom/leaf) sub-tree with another. That was the final straw that got me to realize the contortions I was going through to save a few type_tree nodes (cons cells). Switching to the new approach was hard partly because I've been using the old approach for so long and type_tree manipulations had pervaded everything. Another issue I ran into was the realization that my layers were not cleanly separated. Key parts of early layers (precomputing type metadata) existed purely for far later ones (shape-shifting types). Layers I got repeatedly stuck at: 1. the transform for precomputing type sizes (layer 30) 2. type-checks on merge instructions (layer 31) 3. the transform for precomputing address offsets in types (layer 36) 4. replace operations in supporting shape-shifting recipes (layer 55) After much thrashing I finally noticed that it wasn't the entirety of these layers that was giving me trouble, but just the type metadata precomputation, which had bugs that weren't manifesting until 30 layers later. Or, worse, when loading .mu files before any tests had had a chance to run. A common failure mode was running into types at run time that I hadn't precomputed metadata for at transform time. Digging into these bugs got me to realize that what I had before wasn't really very good, but a half-assed heuristic approach that did a whole lot of extra work precomputing metadata for utterly meaningless types like `((address number) 3)` which just happened to be part of a larger type like `(array (address number) 3)`. So, I redid it all. I switched the representation of types (because the old representation made unit tests difficult to retrofit) and added unit tests to the metadata precomputation. I also made layer 30 only do the minimal metadata precomputation it needs for the concepts introduced until then. In the process, I also made the precomputation more correct than before, and added hooks in the right place so that I could augment the logic when I introduced shape-shifting containers. == lessons learned There's several levels of hygiene when it comes to layers: 1. Every layer introduces precisely what it needs and in the simplest way possible. If I was building an app until just that layer, nothing would seem over-engineered. 2. Some layers are fore-shadowing features in future layers. Sometimes this is ok. For example, layer 10 foreshadows containers and arrays and so on without actually supporting them. That is a net win because it lets me lay out the core of Mu's data structures out in one place. But if the fore-shadowing gets too complex things get nasty. Not least because it can be hard to write unit tests for features before you provide the plumbing to visualize and manipulate them. 3. A layer is introducing features that are tested only in later layers. 4. A layer is introducing features with tests that are invalidated in later layers. (This I knew from early on to be an obviously horrendous idea.) Summary: avoid Level 2 (foreshadowing layers) as much as possible. Tolerate it indefinitely for small things where the code stays simple over time, but become strict again when things start to get more complex. Level 3 is mostly a net lose, but sometimes it can be expedient (a real case of the usually grossly over-applied term "technical debt"), and it's better than the conventional baseline of no layers and no scenarios. Just clean it up as soon as possible. Definitely avoid layer 4 at any time. == minor lessons Avoid unit tests for trivial things, write scenarios in context as much as possible. But within those margins unit tests are fine. Just introduce them before any scenarios (commit 3297). Reorganizing layers can be easy. Just merge layers for starters! Punt on resplitting them in some new way until you've gotten them to work. This is the wisdom of Refactoring: small steps. What made it hard was not wanting to merge *everything* between layer 30 and 55. The eventual insight was realizing I just need to move those two full-strength transforms and nothing else.
* 3259Kartik K. Agaram2016-08-261-1/+1
| | | | | | | | | | | Prefer preincrement operators wherever possible. Old versions of compilers used to be better at optimizing them. Even if we don't care about performance it's useful to make unary operators look like unary operators wherever possible, and to distinguish the 'statement form' which doesn't care about the value of the expression from the postincrement which usually increments as a side-effect in some larger computation (and so is worth avoiding except for some common idioms, or perhaps even there).
* 3239Kartik K. Agaram2016-08-211-1/+1
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* 3212 - bugfix in refcount managementKartik K. Agaram2016-08-171-16/+6
| | | | | | | | | | | When updating refcounts for a typed segment of memory being copied over with another, we were only ever using the new copy's data to determine any tags for exclusive containers. Looks like the right way to do refcounts is to increment and decrement separately. Hopefully this is a complete fix for the intermittent but non-deterministic errors we've been encountering while running the edit/ app.
* 3211Kartik K. Agaram2016-08-171-1/+1
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* 3209Kartik K. Agaram2016-08-171-3/+3
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* 3202 - bugfix: 'start-running' and refcountsKartik K. Agaram2016-08-161-1/+3
| | | | | | | | | | | | | | | | | | | | | | When you pass an ingredient to a recipe using 'start-running' it mostly behaves identically to performing a regular function call. However, if the calling function completed before the new routine had a chance to run, the ingredients passed in ran the risk of being reclaimed. In response, let's always increment refcounts at the time of a function call rather than when the ingredients are read inside the callee. Now the summary of commit 3197 is modified to this: Update refcounts of products after every instruction, EXCEPT: a) when instruction is a non-primitive and the callee starts with 'local-scope' (because it's already not decremented in 'return') OR: b) when instruction is primitive 'next-ingredient' or 'next-ingredient-without-typechecking'
* 3070Kartik K. Agaram2016-06-281-9/+4
| | | | | Extract out the implementation of 'allocate' so other instructions (ahem, deep-copy) can use it.
* 2972 - abandon recursive containersKartik K. Agaram2016-05-171-7/+114
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* 2970Kartik K. Agaram2016-05-171-4/+4
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* 2968Kartik K. Agaram2016-05-171-2/+2
| | | | | | | | | | | | | | | | | | | | | | | More reorganization in preparation for implementing recursive abandon(). Refcounts are getting incredibly hairy. I need to juggle containers containing other containers, and containers *pointing* to other containers. For a while I considered getting rid of address_element_info entirely and just going by types for every single update_refcount. But that's definitely more work, and it's unclear that things will be cleaner/shorter/simpler. I haven't measured the speedup, but it seems worth optimizing every pointer copy to make sure we aren't manipulating types at runtime. The key insight now is a) to continue to compute information about nested containers at load time, because that's the common case when updating refcounts, but b) to compute information about *pointed* values at run-time, because that's the uncommon case. As a result, we're going to cheat in the interpreter and use type information at runtime just for abandon(), just because the corresponding task when we get to a compiler will be radically different. It will still be tractable, though.
* 2961Kartik K. Agaram2016-05-151-1/+1
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* 2927Kartik K. Agaram2016-05-051-6/+9
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* 2922Kartik K. Agaram2016-05-041-20/+4
| | | | | | | | | A better primitive: manage refcounts for an assignment without actually doing the assignment itself. This way we can add refcounts as a new, independent bit of bookkeeping without littering early returns and duplicate code paths. (OCD: commit number.)
* 2898 - start filling in missing refcountsKartik K. Agaram2016-05-031-0/+1
| | | | | | | This commit covers instructions 'put', 'put-index' and 'maybe-convert'. Next up are the harder ones: 'copy' and 'merge'. In these cases there's a non-scalar being copied, and we need to figure out which locations within it need to update their refcount.
* 2897Kartik K. Agaram2016-05-031-0/+143