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make liveSlots honor dropExports #2664

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warner opened this issue Mar 17, 2021 · 0 comments
Closed

make liveSlots honor dropExports #2664

warner opened this issue Mar 17, 2021 · 0 comments
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enhancement New feature or request SwingSet package: SwingSet

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warner commented Mar 17, 2021

What is the Problem Being Solved?

A later stage of #2615 is to have liveslots fully implement dispatch.dropExports. Right now, dropExports is a no-op: it runs without crashing, but doesn't actually cause the vat to forget anything.

Once #2660 is done, there will be an exported Set object that holds a strong reference to every Remotable that has been exported (since the slotToVal table will no longer hold strong references, merely WeakRefs). The dropExports function must be changed to look up the Remoteable and delete it from exported.

It should also remove the vref from slotToVal and valToSlot. That might be trivial, but I need to think about how this might interact with the finalizers (ideally it shouldn't) and the remaining state of the tables.

Test Plan

After implementing this, and enough kernel reference-counting support to trigger it, we can probably do an end-to-end test, although I'm not sure how to measure the export side. Testing GC code is always tricky.
@warner warner added enhancement New feature or request SwingSet package: SwingSet labels Mar 17, 2021
@warner warner self-assigned this Mar 17, 2021
@warner warner mentioned this issue Mar 17, 2021
Closed
11 tasks
warner added a commit that referenced this issue Mar 17, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
1eb19e6 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

refs #2660
@warner warner mentioned this issue Mar 17, 2021
Closed
warner added a commit that referenced this issue Mar 17, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
d15c506 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

refs #2660
warner added a commit that referenced this issue Mar 17, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
c9af540 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

refs #2660
warner added a commit that referenced this issue Apr 21, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
50c75d8 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`. We remove imported objects from the deadSet
if/when they are re-introduced.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

We only register finalizers for imported objects: not imported promises, and
not exports of any flavor.

Liveslots is not yet calling syscall.dropImports, but by mocking WeakRef and
FinalizationRegistry, we can test to make sure it updates the deadSet
correctly.

refs #2660
warner added a commit that referenced this issue Apr 23, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
c243129 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`. We remove imported objects from the deadSet
if/when they are re-introduced.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

We only register finalizers for imported objects: not imported promises, and
not exports of any flavor.

Liveslots is not yet calling syscall.dropImports, but by mocking WeakRef and
FinalizationRegistry, we can test to make sure it updates the deadSet
correctly.

refs #2660
warner added a commit that referenced this issue Apr 23, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
7394953 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`. We remove imported objects from the deadSet
if/when they are re-introduced.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

We only register finalizers for imported objects: not imported promises, and
not exports of any flavor.

Liveslots is not yet calling syscall.dropImports, but by mocking WeakRef and
FinalizationRegistry, we can test to make sure it updates the deadSet
correctly.

refs #2660
warner added a commit that referenced this issue Apr 23, 2021
@warner
feat(swingset): add WeakRef tracking to liveslots
6309e5f 
Liveslots now uses WeakRefs and a FinalizationRegistry to track the state of
each import: UNKNOWN -> REACHABLE -> UNREACHABLE -> COLLECTED -> FINALIZED ->
UNKNOWN. Reintroduction can move it from UNREACHABLE/COLLECTED/FINALIZED back
to REACHABLE at any time.

Liveslots maintains a local `deadSet` that contains all the vrefs which are
in the FINALIZED state. They will remain in that state (and in `deadSet`)
until a later change which uses `syscall.dropImports` to inform the kernel,
and remove them from `deadSet`. We remove imported objects from the deadSet
if/when they are re-introduced.

Promises are retained until resolved+retired, even if userspace somehow drops
all references to them. We might do better in the future, but the story is a
lot more complicated than it is for Presences.

Exported Remotables are still retained indefinitely. A later change (#2664)
will wire `dropExports()` up to drop them.

We only register finalizers for imported objects: not imported promises, and
not exports of any flavor.

Liveslots is not yet calling syscall.dropImports, but by mocking WeakRef and
FinalizationRegistry, we can test to make sure it updates the deadSet
correctly.

refs #2660
@warner warner mentioned this issue May 16, 2021
Closed
9 tasks
@warner warner closed this as completed Jun 18, 2021
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