This commit is an optimization: avoiding destruction of
foreign objects on the wrong shard. Releasing objects allocated on a
different shard causes their ::free calls to be executed remotely,
which adds unnecessary load to the SMP subsystem.
Before this patch, a std::vector could be moved
to another shard. When the vector was eventually destroyed,
its ::free had to be marshalled back to the shard where the memory had
originally been allocated. This change avoids that overhead by passing
the vector by const reference instead.
The referenced objects lifetime correctness reasoning:
* the put_or_delete_item refs usages in put_or_delete_item_cas_request
are bound to its lifetime
* cas_request lifetime is bound to storage_proxy::cas future
* we don't release put_or_delete_item-s untill all storage_proxy::cas
calls are done.
f00f7976c1