Make Insert/Delete refuse unsafe operation (option 3) #88
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We receicently had [a panic in Consul](hashicorp/consul#9566) that was caused by incorrect usage of a ResultIterator. A minimal reproduction of this panic can be seen [here](https://github.com/hashicorp/go-memdb/compare/panic-delete-inside-iter). Many of us learned that there are undocumented rules for using a ResultIterator correct with a write transaction. This commit attempts to document that safe use of a ResultIterator.
This was referenced Jan 22, 2021
dnephin
commented
Jan 22, 2021
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| func (txn *Txn) checkActiveIterator() error { | ||
| if txn.activeIterators > 0 { | ||
| return fmt.Errorf("operation is not safe from within a ResultIteration.Next loop") |
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I think this error message can be improved, but I'll wait to see what others thing about this option.
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This is one option for making the code behave correctly in the scenario described in #85 (other options in #86, #87).
Instead of a panic, make any mutation operation (Insert, Delete*) report an error if there are any iterations that have not been exhausted. This unfortunately requires a change to the interface in the rare case where an iterator is not exhausted in a for loop.
TODO: