# Barbershop

Barbershop is a fast, lightweight priority queue system. The goal is to
create a dead simple network service with libevent to manage priority
queue.

# Dependencies
check >= 0.8.2
libevent >= 1.4.13
pkgconfig >= 0.25 (possibly lower versions would work)

# Compilitaion Notes

Normally all that should be needed is to compile:
./bootstrap.sh
./configure
make

If there is issues with libtool versions when running make, you can run:
libtoolize	[or glibtoolize]
./bootstrap.sh
./configure
make
 
# Usage

This application exists to allow priority queue workers to scale out. The
idea is that for a given dataset (a list of numbers), some things need to be
processed periodical and the order in which they processed may change over
time. The workers shouldn't have to concern themselves with the why or how
of a priority change, just which item to process next.

Over a period of time, clients send update calls to barbershop:

    UPDATE 61231 4
    UPDATE 12353 1
    UPDATE 12342 1

Workers want the next item to be processed:

    NEXT

Monitors want to know the state of the system through info calls:

    INFO

# Protocol

This protocol is based loosely on the Redis protocol specification.

    http://code.google.com/p/redis/wiki/ProtocolSpecification

A client connects to a Barbershop server creating a TCP connection to the
port 8002. Every barbershop command or data transmitted by the client and
the server is terminated by "\r\n" (CRLF).

The simplest commands are the inline commands. This is an example of a
server/client chat (the server chat starts with S:, the client chat with C:).

    C: UPDATE 61231 5\r\n
    S: +OK\r\n
    C: NEXT\r\n
    S: +61231\r\n

An inline command is a CRLF-terminated string sent to the client. The server
can reply to commands in different ways:

    With an error message (the first byte of the reply will be "-")
    With a single line reply (the first byte of the reply will be "+)

This service does not support bulk commands or responses.

## Commands

There are only a handful of commands supported at this point.

'UPDATE <item id> <value>'

Update the priority of a given item by X.

    C: UPDATE 61231 5\r\n
    S: +OK\r\n

'NEXT'

Return the next item in the queue.

    C: NEXT\r\n
    S: +61231\r\n

When there are no more items to return a '-1' is returned.

    C: NEXT\r\n
    S: +-1\r\n

'PEEK'

Return the next item in the queue without removing it from the queue.

    C: PEEK\r\n
    S: +61231\r\n

When there are no more items to return a '-1' is returned.

    C: PEEK\r\n
    S: +-1\r\n

'SCORE <item id>'

Return the score of a given item.

    C: SCORE 61231\r\n
    S: +5\r\n

If the item does not exist or have a score then a '-1' is returned.

    C: SCORE 61231\r\n
    S: +-1\r\n

'INFO'

Return some server stats. This command deviates from the standard response
format by returning a list of key-value pairs separated by a ':'.

* 'uptime' (32u) Number of seconds this server has been running.
* 'version' (string) Version string of this server.
* 'updates' (32u) Number of update commands received by this server.
* 'items' (32u) Number of items.
* 'pools' (32u) Number of pools.

    C: INFO\r\n
    S: uptime:60000\r\n
    S: version:0.2.1\r\n
    S: updates:9742851\r\n
    S: items:2132931\r\n
    S: pools:47831\r\n