Calle Wilund e667dcc3d0 commitlog: Make segment->segment_manager relation shared pointer ...

The segment->segment_manager pointer has, until now, been a raw pointer,
which in a way is sensible, since making circular shared pointer
relations is in general bad. However, since the code and life cycle
of segments has evolved quite a bit since that initial relation
was defined, becoming both more and then suddenly, in a sense,
less, asynchronous over time, the usage of the relation is in fact
more consistent with a shared pointer, in that a segment needs to
access its manager to properly do things like write and flush.

These two ops in particular depend on accessing the segment manager
in a way that might be fine even using raw pointers, if it was not
again for that little annoying thing of continuation reordering.

So, lets just make the relation a shared pointer, solving the issue
of whether the manager is alive when a segment accesses it. If it
has been "released" (shut down), the existing mechanisms (gate)
will then trigger and prevent any actual _actions_ from taking
place. And we don't have to complicate anything else even more.

Only "big" change is that we need to explicitly orphan all
segments in commitlog destructor (segment_manager is essentially
a p-impl).

This fixes some spurious crashes in nightly unit tests.

Fixes #966.

Message-Id: <1456838735-17108-1-git-send-email-calle@scylladb.com>

2016-03-01 16:48:28 +02:00

11 KiB

Raw Blame History

View Raw