59013 - hash table inconsistency in nsReplacementPolicy

Status: VERIFIED FIXED

(Core :: Networking: Cache, defect, P3)

Description

[scottputterman]

I thought that my changes to 58186 were causing this but it turns out that they
just made this more noticeable since it made it possible to get into this situation.

In nsReplacementPolicy::DeleteCacheEntry I often his this assertion:

    NS_ASSERTION(0, "hash table inconsistency");

I think I know the reason why now. When loading all of the records from the disk
we create a dbenumerator and call GetNext on it. However, GetNext always returns
the same record, it just fills in the data using the same memory. The comment
actually says that if you want to keep around an individual record that you need
to clone or dup it. What ends up happening is that in
AssociateCacheEntryWithRecord we continually add cacheentries to mRankedEntries
that are all pointing to the same record. As each new record is filled in, they
all end up pointing to the same data instead of the data they used to point to.

Now, when we are trying to delete entries so we can add more, we might actually
delete one of these records that has a duplicate. That means that when we try to
delete another one of these records, when it gets to DeleteCacheEntry, it won't
be able to find a record to delete and it will give that assertion. Basically, I
think we need to dup or clone these records so that each cache entry has its own
record.

Comment 1

[neeti]

Will be resolved when new cache code lands.

Comment 2

[Tom Everingham]

marking fixed per engineers comments and that new cache has landed

Comment 3

[Tom Everingham]

verified