There were inconsistencies in the order in which entity locks were taken
when multiple entities needed to be locked at the same time. In most
cases, the order was first locking entity X, then locking the parent
entity of X. However, in some cases the order was reversed, a likely
cause of deadlocks.
This commit sorts these problems, and in particular propagating
operations into children. The entity refcount is now part of the handle
administration so that it is no longer necessary to lock an entity to
determine whether it is still allowed to be used (previously it had to
check the CLOSED flag afterward). This allows recursing into the
children while holding handles and the underlying objects alive, but
without violating lock order.
Attendant changes that would warrant there own commits but are too hard
to split off:
* Children are now no longer in a singly linked list, but in an AVL
tree; this was necessary at some intermediate stage to allow unlocking
an entity and restarting iteration over all children at the "next"
child (all thanks to the eternally unique instance handle);
* Waitsets shifted to using arrays of attached entities instead of
linked lists; this was a consequence of dealing with some locking
issues in reading triggers and considering which operations on the
"triggered" and "observed" sets are actually needed.
* Entity status flags and waitset/condition trigger counts are now
handled using atomic operations. Entities are now classified as
having a "status" with a corresponding mask, or as having a "trigger
count" (conditions). As there are fewer than 16 status bits, the
status and its mask can squeeze into the same 32-bits as the trigger
count. These atomic updates avoid the need for a separate lock just
for the trigger/status values and results in a significant speedup
with waitsets.
* Create topic now has a more rational behaviour when multiple
participants attempt to create the same topic: each participant now
gets its own topic definition, but the underlying type representation
is shared.
Signed-off-by: Erik Boasson <eb@ilities.com>
647f7466d6