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References between arenas
=========================
Outer-to-inner:
* This does NOT work because:
* the inner arena might have a shorter lifetime, and
* on exception, the inner arena will be invalidated,
but not necessarily the outer arena.
Inner-to-outer:
* This should work.
Related problem: Accessing data from other areans
-------------------------------------------------
func arena Thing.do_stuff(ref var Node n)
{
n.locked = true
n.value /= this.divisor # could be 0
n.locked = false
}
Exceptions are supposed to invalidate/kill all arenas that are reachable
from the call chain.
In this case, n could be used by an arena that is not a sub-arena
of the "this" arena. So the arena of "n" probably need to be invalidated
as well. Otherwise, "n" could get stuck in an intermediate state.
Solutions:
- Disallow passing "ref var" across exception isolation boundaries.
Exceptions: "ref var threaded"
Related: How to handle exceptions?
----------------------------------
SLUL does not use thread-local state, but uses arenas instead.
Solution:
- Allow only exceptions in functions that have an arena either as
the receiver (for methods) or as the first parameter (for non-methods).
- Invalidation of the callee-arena must invalidate all arenas in the current
isolation boundary, but should not invalidate any other arenas.
=> All arenas should have a pointer to the current exception isolation
boundary.
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