fixes #461 Context support for SUB

fixes #762 Pub/Sub very slow compared with nanomsg

This introduces contexts for SUB, and converts both the cooked SUB
and PUB protocols to use a new lightweight message queue that has
significant performance benefits over the heavy-weight message queue.

We've also added a test program, pubdrop, in the perf directory,
which can be used for measuring pub/sub message rates and drop rates.
Note that its quite easy to overwhelm a subscriber still.

The SUB socket performance is still not completely where it needs to be.
There are two remainging things to improve.  Firsst we need to replace
the naive linked list of topics with a proper PATRICIA trie.  Second, we
need to work on the low level POSIX poller code.  (The Windows code is
already quite good, and we outperform nanomsg on Windows.)

0 files changed, 0 insertions, 0 deletions