Introduction

Stoplight is a distributed mutex server, based on the Sigma algorithm.

Mutual exclusion: No two different clients are in their critical sections at the same time.

Features:

progress guaranteed in the face of process crashes (i.e. lockout-freedom, will not deadlock)
assumes asynchronous and unreliable communication
survives server and client memory loss
endures messages being lost, duplicated or delivered out of order (non-FIFO)
mutual exclusion guaranteed if f<n/3 where f is the number of failed servers and n is the total number of servers.

Install

Prerequisites

ruby / rubygems / rake
gem sources --add http://gems.github.com
gem install auser-skelerl auser-dslify

Build

cd stoplight
rake

Layout

    .
    |-- EMakefile
    |-- INSTALL
    |-- README.mkd
    |-- deps                 # dependencies
    |-- doc                  # documentation
    |-- ebin                 # app, bootscripts, ebin files
    |-- include              # headers 
    |-- priv
    |   `-- tasks            # rake tasks
    |-- scripts              # scripts to start/stop stoplight
    |-- src                  # main source
    `-- test                 # tests

Testing Locally

Open three windows:

window 1.

STOPLIGHT_NODENAME="stoplight@your-ip" ./scripts/stoplight-server

window 2.

STOPLIGHT_SERVER="stoplight@your-ip" ./scripts/stoplight-client
1> {Resp, Pid} = stoplight_client:lock(green, 1000).
{crit,<6078.82.0>}

window 3.

STOPLIGHT_SERVER="stoplight@your-ip" ./scripts/stoplight-client
1> {Resp, Lob} = stoplight_client:lock(green).        
{no,<6078.91.0>}

back to 2.

2> stoplight_client:release(Pid).
ok

back to 3.

2> {Resp2, Lob2} = stoplight_client:lock(green).
{crit,<6078.91.0>}

Clustering

On Server Machine 1

STOPLIGHT_NODENAME="stoplight@192.168.133.128" ./scripts/stoplight-server

On Server Machine 2

STOPLIGHT_NODENAME="stoplight@192.168.1.66" STOPLIGHT_SERVER="toplight@192.168.133.128" ./scripts/stoplight-server
1> nodes().
['stoplight@192.168.133.128']

On Client Machine

STOPLIGHT_SERVER="stoplight@192.168.133.128" ./scripts/stoplight-client

Configuration

stoplight servers is a valid application configuration option. This means when starting the server you can specify a list of addresses to other servers like so:

STOPLIGHT_NODENAME='stoplight@192.168.1.66' STOPLIGHT_SERVER_START_ARGS="-stoplight servers ['stoplight@192.168.133.128']" ./scripts/stoplight-server

Acknowledgements

Stoplight Icon by alessandro "mentalrey" rei from his KDE "Dark Glass Icon Project" - http://www.mentalrey.it/project.html

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