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?
Plan:
1. Fix a hole where addresses are shared between routines when passed in
as arguments to `start-running`.
2. Switch to a new approach to refcount management: instead of updating
refcounts when writing products of instructions by default, increment
refcounts inside instructions by default and decrement refcounts in
caller. More details in future when I actually implement this.
3. Now we shouldn't need a distinction between `new-default-space` and
`local-scope`, and all functions can simply decrement refcounts of
their default-space, consistently handling any refcounts in the space.
At this point if all goes well, continuations should be safe!
This commit is just preparation for step 1.
Kartik Agaram