pgsql: Single-reader, single-writer, lightweight shared message queue.

Single-reader, single-writer, lightweight shared message queue.

This code provides infrastructure for user backends to communicate
relatively easily with background workers.  The message queue is
structured as a ring buffer and allows messages of arbitary length
to be sent and received.

Patch by me.  Review by KaiGai Kohei and Andres Freund.

Branch
------
master

Details
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http://git.postgresql.org/pg/commitdiff/ec9037df2634ddcd6a3b036463722c8ee009b132

Modified Files
--------------
src/backend/storage/ipc/Makefile |    2 +-
src/backend/storage/ipc/shm_mq.c |  945 ++++++++++++++++++++++++++++++++++++++
src/include/storage/shm_mq.h     |   70 +++
3 files changed, 1016 insertions(+), 1 deletion(-)