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* 3309Kartik K. Agaram2016-09-091-23/+323
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 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.
* 3304Kartik K. Agaram2016-09-071-3/+3
| | | | | | Highlight a couple of places where it turns out that we're flying by the seat of our pants with heuristics, and we don't really understand how to precompute metadata for a program's types.
* 3300Kartik K. Agaram2016-09-061-1/+2
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* 3256Kartik K. Agaram2016-08-261-1/+2
| | | | | Bugfix in filesystem creation. I'm sure there are other fake-filesystem bugs.
* 3212 - bugfix in refcount managementKartik K. Agaram2016-08-171-27/+75
| | | | | | | | | | | 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. Agaram2016-08-171-1/+1
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* 3208Kartik K. Agaram2016-08-161-28/+12
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* 3207Kartik K. Agaram2016-08-161-0/+17
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* 3206Kartik K. Agaram2016-08-161-1/+1
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* 3205Kartik K. Agaram2016-08-161-13/+13
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* 3202 - bugfix: 'start-running' and refcountsKartik K. Agaram2016-08-161-4/+10
| | | | | | | | | | | | | | | | | | | | | | 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'
* 3199Kartik K. Agaram2016-08-161-6/+4
| | | | | | | | | Never mind, just close your nose and replace that function parameter with a global variable. This may not always be the solution for the problem of layers being unable to add parameters and arguments, but here it works well and it's unclear what problems the global might cause.
* 3197Kartik K. Agaram2016-08-161-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Replace an integer with a boolean across two layers of function calls. It has long been one of the ugliest consequences of my approach with layers that functions might need to be introduced with unnecessary arguments simply because we have no clean way to add parameters to a function definition after the fact -- or to add the default argument corresponding to that parameter in calls. This problem is exacerbated by the redundant argument having to be passed in through multiple layers of functions. In this instance: In layer 20 we define write_memory with an argument called 'saving_instruction_products' which isn't used yet. In layer 36 we reveal that we use this argument in a call to should_update_refcounts_in_write_memory() -- where it is again not used yet. Layer 43 finally clarifies what we're shooting for: a) In general when we need to update some memory, we always want to update refcounts. b) The only exception is when we're reclaiming locals in a function that set up its stack frame using 'local-scope' (signalling that it wants immediate reclamation). At that point we avoid decrementing refcounts of 'escaping' addresses that are being returned, and we also avoid incrementing refcounts of products in the caller instruction. The latter case is basically why we need this boolean and its dance across 3 layers. In summary, write_memory() needs to update refcounts except if: we're writing products for an instruction, the instruction is not a primitive, and the (callee) recipe for the instruction starts with 'local-scope'.
* 3190Kartik K. Agaram2016-08-161-2/+7
| | | | | | | | | | | | I'm seeing *extremely* rare crashes due to some problem with negative refcounts in the edit/ app. It's not using any concurrency at all, so that's not the issue. Setting a tripwire to try and catch it. I'm going to run: mu --trace edit ..all the time for a while. And periodically restart when the trace makes the program too sluggish to continue.
* 3124Kartik K. Agaram2016-07-221-1/+0
| | | | | Reorganize data structure for lambda cells. Create our first real unit test for the compiler in the process.
* 3059Kartik K. Agaram2016-06-171-0/+2
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* 3047 - fix another hole in refcount managementKartik K. Agaram2016-06-111-26/+56
| | | | | | This wouldn't have failed silently; I have that fig leaf. If someone had tried to copy an exclusive container containing an exclusive container containing an address Mu would have crashed on them.
* 3045 - generalize core refcounting data structureKartik K. Agaram2016-06-111-24/+67
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* 3044Kartik K. Agaram2016-06-111-0/+1
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* 3043Kartik K. Agaram2016-06-101-18/+9
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* 3042Kartik K. Agaram2016-06-101-2/+2
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* 3018Kartik K. Agaram2016-05-261-5/+2
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* 2973 - reclaim refcounts for local scopes againKartik K. Agaram2016-05-181-6/+14
| | | | | | More thorough redo of commit 2767 (Mar 12), which was undone in commit 2810 (Mar 24). It's been a long slog. Next step: write a bunch of mu code in the edit/ app in search of bugs.
* 2972 - abandon recursive containersKartik K. Agaram2016-05-171-8/+14
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* 2968Kartik K. Agaram2016-05-171-14/+37
| | | | | | | | | | | | | | | | | | | | | | | 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.
* 2966Kartik K. Agaram2016-05-171-6/+3
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* 2965 - update refcounts when copying containersKartik K. Agaram2016-05-151-47/+131
| | | | | | This is hopefully quite thorough. I handle nested containers, as well as exclusive containers that might contain addresses only when the tag has a specific value.
* 2963Kartik K. Agaram2016-05-151-38/+42
| | | | | | To support exclusive containers a recursive answer will be easier to reuse than the current iterative one. First step: figure out the precise boundary and interface of the recursive function.
* 2962Kartik K. Agaram2016-05-151-0/+3
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* 2961Kartik K. Agaram2016-05-151-2/+2
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* 2960Kartik K. Agaram2016-05-151-7/+7
| | | | First genuine Travis CI failure fixed! May there be many more.
* 2959Kartik K. Agaram2016-05-141-7/+71
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* 2958Kartik K. Agaram2016-05-141-1/+30
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* 2957Kartik K. Agaram2016-05-141-8/+57
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* 2956Kartik K. Agaram2016-05-141-3/+7
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* 2955 - back to more refcount housekeepingKartik K. Agaram2016-05-121-0/+108
| | | | | Update refcounts of address elements when copying containers. Still lots to do; see todo list at end of 036refcount.cc.
* 2934 - all layers running againKartik K. Agaram2016-05-071-2/+2
| | | | | | Since I switched to a Mac laptop (commit 2725) I've been lax in running test_all_layers because I have to ssh into a server and whatnot. I should just get CI setup somewhere..
* 2933Kartik K. Agaram2016-05-061-1/+1
| | | | Can't believe I didn't run tests after 2932.
* 2931 - be explicit about making copiesKartik K. Agaram2016-05-061-2/+2
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* 2923Kartik K. Agaram2016-05-041-3/+0
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* 2922Kartik K. Agaram2016-05-041-28/+34
| | | | | | | | | 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. Agaram2016-05-031-6/+91
| | | | | | | 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/+74