Weighted reference count
- Use weights associated with remote references.
- The initial weight for the concrete objects is a constant value N.
- Sending a reference from P to Q divides the reference weight stored
for P and Q.
- The sum of all weights is N.
- The clean call return the weight of the deleted reference to the
concrete object.
- The concrete object may be recycled when its weight is N.
- No dirty calls.
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