When the root task fails the process fails. Failures on other tasks propagate
up the task tree. Failures on non-root tasks without parents just
(theoretically) unwind and disappear.
The first is that the memory_region destructor would complain there is
still an outstanding allocation. This is because circular_buffer from
rust_chan wasn't refing its task, so the task was being destructed too
soon.
The second was where the program could deadlock while joining a
task. The target task would die in the time between checking whether
the task should block and then actually blocking. The fix is to use
the target task's lock.
Ports and channels have been moved to the kernel pool, since they've
been known to outlive their associated task. This probably isn't the
right thing to do, the life cycle needs fixed instead.
Some refactorying in memory_region.cpp. Added a helper function to
increment and decrement the allocation counter. This makes it easier
to switch between atomic and non-atomic increments. Using atomic
increments for now, although this still does not fix the problem.
The duplication of upcalls is due to the fact that the runtime is
shared between stage0/rustc and stage1/rustc. Once snapshots are
updated, they should be de-duplicated.
The callback happens when a task moves from the "blocked" state to the
"running" state. The callback is also inherited by child tasks. There
is currently only a native API.
This code hasn't been heavily exercised yet.
If the channel is associated with a port then the destructor will assert.
Additionally, destruction of the object is not always appropriate. This brings
the deref() method into sync with the behavior of generated rust code which
only invokes destroy() once the reference count goes to 0.
The macro with the extra dtor parameter is intended for structures like
rust_chan which may not necessarily delete themselves when the ref count
becomes 0. This functionality will be used in an upcoming changeset.
