I've been working on this slowly over several weeks, but it's too hard
to support 0 as the null value for addresses. I constantly have to add
exceptions for scalar value corresponding to an address type (now
occupying 2 locations). The final straw is the test for 'reload':
x:num <- reload text
'reload' returns an address. But there's no way to know that for
arbitrary instructions.
New plan: let's put this off for a bit and first create support for
literals. Then use 'null' instead of '0' for addresses everywhere. Then
it'll be easy to just change what 'null' means.
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?
Cleaning up the console interfaces before we start changing the socket
interfaces to look like them. Reading from sockets need to be
non-blocking just like reading from the console.
Better implementation of commit 3445: not requiring types for special
variables in scenarios. It turned out that it wasn't working anytime we
needed to call 'get' on a special variable inside a scenario. After
moving that work to an earlier transform we can now use 'filesystem'
without a type inside scenarios.
Ugly that we didn't need 'screen' to provide a type in scenarios
(because assume-screen expands to a definition of 'screen') but we did
need a type for 'console'. Just never require types for special names in
scenarios.
Undo 3272. The trouble with creating a new section for constants is that
there's no good place to order it since constants can be initialized
using globals as well as vice versa. And I don't want to add constraints
disallowing either side.
Instead, a new plan: always declare constants in the Globals section
using 'extern const' rather than just 'const', since otherwise constants
implicitly have internal linkage (http://stackoverflow.com/questions/14894698/why-does-extern-const-int-n-not-work-as-expected)
Move global constants into their own section since we seem to be having
trouble linking in 'extern const' variables when manually cleaving mu.cc
into separate compilation units.
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).
Standardize quotes around reagents in error messages.
I'm still sure there's issues. For example, the messages when
type-checking 'copy'. I'm not putting quotes around them because in
layer 60 I end up creating dilated reagents, and then it's a bit much to
have quotes and (two kinds of) brackets. But I'm sure I'm doing that
somewhere..
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.
Turns out that LLVM/Clang still doesn't support multiplying 64-bit
numbers on a 32-bit platform.
https://llvm.org/bugs/show_bug.cgi?id=14469
This is just a quick fix, because it turns out I don't have any integer
multiplication anywhere else. In the long run I think I'm going to just
drop 'long long int' in favor of 'int'. Overflow is less likely than
this configuration on somebody's machine.
This uncovered a second bug (besides 2766) -- I was manually doing the
work of 'new-fake-console' inside 'assume-console' but forgetting to
increment a refcount.
We don't yet actually maintain the refcount. That's next.
Hardest part of this was debugging the assume-console scenarios in layer
85. That took some detailed manual diffing of traces (because the output
of diff was no good).
New tracing added in this commit add 8% to .traces LoC. Commented out
trace() calls (used during debugging) make that 45%.
This is the one major refinement on the C programming model I'm planning
to introduce in mu. Instead of Rust's menagerie of pointer types and
static checking, I want to introduce just one new type, and use it to
perform ref-counting at runtime.
So far all we're doing is updating new's interface. The actual
ref-counting implementation is next.
One implication: I might sometimes need duplicate implementations for a
recipe with allocated vs vanilla addresses of the same type. So far it
seems I can get away with just always passing in allocated addresses;
the situations when you want to pass an unallocated address to a recipe
should be few and far between.
Kartik Agaram