fix(SwingSet): VOM retains Remotables used in virtualized data #3153
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Userspace might store a locally-created Remotable (e.g. `Far('iface',
{methods..})` in the `state` of a virtual object, or somewhere in the value
of a vref-keyed `makeWeakStore()` entry. In either case, the data is
virtualized: serialized and written to disk. This serialized form obviously
cannot keep the Remotable JS `Object` alive directly, however userspace
reasonably expects to get the Remotable back if it reads the `state` or does
a `.get` on the store.
To ensure the Remotable can be looked up from the serialized vref, the
virtual object manager must retain a strong reference to the original
Remotable for as long as its vref is present anywhere in the virtualized
data.
For now, we simply add the Remotable to a strong Set the first time it is
added, and we never remove it. This is safe, but conservative.
To do better (and eventually release the Remotable), we'll need to add some
form of refcount to each vref. When the refcount of the Remotable's vref
drops to zero, the VOM can drop its strong reference to the Remotable.
closes #3132
refs #3106
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Userspace might store a locally-created Remotable (e.g.
Far('iface', {methods..})in thestateof a virtual object, or somewhere in the valueof a vref-keyed
makeWeakStore()entry. In either case, the data isvirtualized: serialized and written to disk. This serialized form obviously
cannot keep the Remotable JS
Objectalive directly, however userspacereasonably expects to get the Remotable back if it reads the
stateor doesa
.geton the store.To ensure the Remotable can be looked up from the serialized vref, the
virtual object manager must retain a strong reference to the original
Remotable for as long as its vref is present anywhere in the virtualized
data.
For now, we simply add the Remotable to a strong Set the first time it is
added, and we never remove it. This is safe, but conservative.
To do better (and eventually release the Remotable), we'll need to add some
form of refcount to each vref. When the refcount of the Remotable's vref
drops to zero, the VOM can drop its strong reference to the Remotable.
closes #3132
refs #3106