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* 4179 - experiment: rip out memory reclamationKartik K. Agaram2018-01-031-552/+2
| | | | | | | | | | | | | | | | | | | | | 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?
* 4176Kartik K. Agaram2017-12-311-1/+1
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* 4139Kartik K. Agaram2017-12-051-6/+1
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* 4138Kartik K. Agaram2017-12-051-2/+2
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* 4115Kartik K. Agaram2017-11-061-3/+5
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* 4104Kartik K. Agaram2017-11-031-4/+4
| | | | | Stop hardcoding Max_depth everywhere; we had a default value for a reason but then we forgot all about it.
* 4089Kartik K. Agaram2017-10-221-12/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Clean up how we reclaim local scopes. It used to work like this (commit 3216): 1. 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', and its result is saved to a variable in the default space (because it's already incremented at the time of the call) 2. If a function starts with 'local-scope', force it to be reclaimed before each return. However, since locals may be returned, *very carefully* don't reclaim those. (See the logic in the old `escaping` and `should_update_refcount` functions.) However, this approach had issues. We needed two separate commands for 'local-scope' (reclaim locals on exit) and 'new-default-space' (programmer takes charge of reclaiming locals). The hard-coded reclamation duplicated refcounting logic. In addition to adding complexity, this implementation failed to work if a function overwrites default-space after setting up a local-scope (the old default-space is leaked). It also fails in the presence of continuations. Calling a continuation more than once was guaranteed to corrupt memory (commit 3986). After this commit, reclaiming local scopes now works like this: Update refcounts of products for every PRIMITIVE instruction. For non-primitive instructions, all the work happens in the `return` instruction: increment refcount of ingredients to `return` (unless -- one last bit of ugliness -- they aren't saved in the caller) decrement the refcount of the default-space use existing infrastructure for reclaiming as necessary if reclaiming default-space, first decrement refcount of each local again, use existing infrastructure for reclaiming as necessary This commit (finally!) completes the bulk[1] of step 2 of the plan in commit 3991. It was very hard until I gave up trying to tweak the existing implementation and just test-drove layer 43 from scratch. [1] There's still potential for memory corruption if we abuse `default-space`. I should probably try to add warnings about that at some point (todo in layer 45).
* 3987Kartik K. Agaram2017-09-011-4/+4
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* 3948Kartik K. Agaram2017-06-241-0/+2
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* 3905Kartik K. Agaram2017-06-101-2/+1
| | | | | | | Standardize exit paths. Most layers now don't need to know about termbox. We can't really use `assert` in console-mode apps; it can't just exit because we want to be able to check assertion failures in tests.
* 3890Kartik K. Agaram2017-05-291-1/+0
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* 3889 - profile refcount updates by recipeKartik K. Agaram2017-05-291-0/+42
| | | | | We're currently spending 50% of our time in `mu edit` performing refcount updates.
* 3875Kartik K. Agaram2017-05-211-16/+15
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* 3841Kartik K. Agaram2017-04-271-2/+2
| | | | | Use the real original instruction in error messages. Thanks Ella Couch.
* 3822Kartik K. Agaram2017-04-141-0/+8
| | | | | | Provide an option to disable memory reclamation. This makes edit/ *much* more responsive. The cost: memory use grows monotonically. Since we no longer have a safe way to reclaim heap allocations, we never do so.
* 3819Kartik K. Agaram2017-04-131-6/+8
| | | | | | | Yet another attempt at trying to clean up commit 3216. I think this solution might finally let me stop agonizing over the problem. State variables for distinguishing call-sites are a reasonable mechanism, orthogonal to waypoints and the hook functions to hold them.
* 3786Kartik K. Agaram2017-03-101-2/+11
| | | | https://www.reddit.com/r/badcode/comments/5xo3qv/its_better_to_have_it_all_on_one_line_right/delodzn
* 3741Kartik K. Agaram2017-02-061-21/+27
| | | | Eliminate a long-standing under-abstraction.
* 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.)
* 3689Kartik K. Agaram2016-11-251-1/+1
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* 3663 - fix a refcounting bug: '(type)' != 'type'Kartik K. Agaram2016-11-101-4/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This was a large commit, and most of it is a follow-up to commit 3309, undoing what is probably the final ill-considered optimization I added to s-expressions in Mu: I was always representing (a b c) as (a b . c), etc. That is now gone. Why did I need to take it out? The key problem was the error silently ignored in layer 30. That was causing size_of("(type)") to silently return garbage rather than loudly complain (assuming 'type' was a simple type). But to take it out I had to modify types_strictly_match (layer 21) to actually strictly match and not just do a prefix match. In the process of removing the prefix match, I had to make extracting recipe types from recipe headers more robust. So far it only matched the first element of each ingredient's type; these matched: (recipe address:number -> address:number) (recipe address -> address) I didn't notice because the dotted notation optimization was actually representing this as: (recipe address:number -> address number) --- One final little thing in this commit: I added an alias for 'assert' called 'assert_for_now', to indicate that I'm not sure something's really an invariant, that it might be triggered by (invalid) user programs, and so require more thought on error handling down the road. But this may well be an ill-posed distinction. It may be overwhelmingly uneconomic to continually distinguish between model invariants and error states for input. I'm starting to grow sympathetic to Google Analytics's recent approach of just banning assertions altogether. We'll see..
* 3654Kartik K. Agaram2016-11-081-8/+12
| | | | | | | | Follow-up to commit 3321: move get_base_type() more thoroughly to layer 55. The notion of a base_type doesn't really make sense before we introduce type ingredients and shape-shifting containers, and it simplifies early layers a *lot* even including the cost of that *ugly* preamble in layer 55 to retrofit all the places.
* 3653Kartik K. Agaram2016-11-081-1/+4
| | | | | | | | | Don't crash on bad types. I need to be more careful in distinguishing between the two causes of constraint violations: bad input and internal bugs. Maybe I should create a second assert() to indicate "this shouldn't really be an assert, but I'm too lazy to think about it right now."
* 3652Kartik K. Agaram2016-11-081-10/+0
| | | | | size_of(type_tree*) is a mess; clean it up with an eye to the final tangled version.
* 3651Kartik K. Agaram2016-11-081-2/+7
| | | | | | 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.
* 3650 - first of a couple of holes in refcountingKartik K. Agaram2016-11-081-0/+58
| | | | We weren't checking within (static) array elements for addresses.
* 3649Kartik K. Agaram2016-11-081-6/+0
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* 3645Kartik K. Agaram2016-11-071-9/+6
| | | | | | 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.
* 3643Kartik K. Agaram2016-11-071-1/+1
| | | | | Standardize on calling literate waypoints "Special-cases" rather than "Cases". Invariably there's a default path already present.
* 3637 - better 'missing type ingredient' errorsKartik K. Agaram2016-11-061-37/+37
| | | | | | | | | | | | Programming languages need some higher-level language construct that's neither an interface nor a class nor an object but a *collection of mutually recursive functions with a well-defined set of entry points and common ingredients. Perhaps the solution here is the Haskell "save your boilerplate" paper. For now I'm going to include the purpose in auxiliary variable names that aren't really necessary for the core processing of a function. Thanks Caleb Couch for reporting this issue.
* 3592 - warn on *any* lookup of address 0Kartik K. Agaram2016-10-251-1/+1
| | | | Thanks Caleb Couch for running into this with $print.
* 3553Kartik K. Agaram2016-10-221-1/+1
| | | | | | | Tag all transforms as idempotent or not. I'd fallen off this wagon. I might even be getting it wrong. Something a type system should automatically verify.
* 3522Kartik K. Agaram2016-10-191-13/+13
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* 3381Kartik K. Agaram2016-09-171-2/+2
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* 3380Kartik K. Agaram2016-09-171-84/+84
| | | | | One more place we were missing expanding type abbreviations: inside container definitions.
* 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.