fix(swingset): only mark refs for processing if refcount hits zero #3380
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There were two bugs in the kernel's garbage-collection handling of orphaned objects (exports of a vat which is later terminated). * Sending a message to an orphaned vat caused the object's refcount to be incremented, but never decremented again, preventing it from being collected. The root cause was `kernelKeeper.kernelObjectExists` using `.owner` to decide whether the object still exists. Orphaned objects have a `.refcount` but no `.owner`. The fix is to just test `.refcount` instead of `.owner`. #3376 * `kernelKeeper.processRefcounts()` wants to check the `isReachable` flag of the exporting vat, to know whether they need a dropExport message, but orphaned objects have no exporting vat anymore. The check crashed the kernel when it attempted to get a vatKeeper for `undefined`. The immediate fix is to skip this check for orphaned objects, which avoids the crash (#3377). But we still need a fix to delete the refcount=0,0 entry (#3378). closes #3376 closes #3377 refs #3378
This should remove some unnecessary work done by `processRefcounts` on objects which have lost one reference, but not all of them. refs #3106
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This should remove some unnecessary work done by
processRefcountsonobjects which have lost one reference, but not all of them.
refs #3106