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Follow-up to commit 3993: deep-copy needs to also ignore screen and
console objects. Basically channels and any fake objects passed into
tests. (The real ones will be null, which will work fine thanks to the
bugfix of commit 3996.)
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Fully isolate routines from their arguments.
I still need exceptions for containers that are *designed* to be
shared between routines. The primary such case is channels; we need some
way to share them between routines, and if we deep-copy them that
defeats their entire purpose.
A milder case is the use of fake file-systems in tests, though that's a
hint that there'll be more of these as the OS gets more fleshed out. The
pattern seems to be that we need to not deep-copy containers that
contain lock fields, and so their operations internally do their own
locking.
We may have to stop hard-coding the list of exceptions and allow people
to define new ones. Perhaps don't deep-copy any container with metadata
of 'shared', and then ensure that get-location is only ever called on
shared containers.
This still isn't absolutely ironclad. People can now store something
into a channel and then pass it into a routine to share arbitrary data.
But perhaps the goal isn't to be ironclad, just to avoid easy mistakes.
I'd still want an automated check for this, though. Some way to
highlight it as an unsafe pattern.
This completes step 1 in the plan of commit 3992 for making
continuations safe.
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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.
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