In several places in the old code, we had problems that only an
in-memory index of diff status could solve, including:
* Remembering which diffs were in-progress, so that we didn't
re-launch them.
* Remembering which diffs had failed, so that we didn't try to
recompute them over and over.
* Having a fast way to look up the diff from a given consensus to
the latest consensus of a given flavor.
This patch adds a hashtable mapping from (flavor, source diff), to
solve the problem. It maps to a cache entry handle, rather than to
a cache entry directly, so that it doesn't affect the reference
counts of the cache entries, and so that we don't otherwise need to
worry about lifetime management.
This conscache flag tells conscache that it should munmap the
document as soon as reasonably possible, since its usage pattern is
expected to not have a lot of time-locality.
Initial tests. These just try adding a few consensuses, looking
them up, and making sure that consensus diffs are generated in a
more or less reasonable-looking way. It's enough for 87% coverage,
but it leaves out a lot of functionality.
This module's job is to remember old consensus documents, to
calculate their diffs on demand, and to .
There are some incomplete points in this code; I've marked them with
"XXXX". I intend to fix them in separate commits, since I believe
doing it in separate commits will make the branch easier to review.
