Assignment 1 – Mazewar Review Session

Assignment 1 –MazewarReview Session CS244B Distributed Systems April 4th, 2014 Wei Shi, Stanford University

Agenda • Logistics • Mazewar • Game rules • Protocol design • Implementation

Logistics • 0% Teams: due April 4, 2014, 11:59pm - Jointly • 40% Design: due April 10, 2014, 11:59pm - Jointly • 40% Program: due April 21, 2014, 11:59pm - Individually • 20% Questions: due April 21, 2014, 11:59pm – Individually • Demo tentatively the week of April 21 • Will post sign-up sheet on Piazza • Local students: in myth clusters(Gates basement) • SCPD: at least one member comes to campus; others join remotely

Game Rules • Rat control • (Done) Movement with a,s,d,f • (Done) Peek left/right with Mouse Left/Right button • Launch missiles with Mouse Middle button • Scoring • Shoot projectile: -1 • Hit opponent: +11 • Opponent hits you: -5 • Player’s view • (done) Map view that shows other players • Rat’s view that shows missile

Game Rules • Only one rat can occupy a square at a time • Rats hit by others should respawn at an unoccupied random location instantly • Cool-down time for firing (time up to you) • Multiple missiles can occupy the same space (speed up to you) • One projectile can hit at most one rat

What You are Given • Implementation of the graphics • Implementation of the basic control • Stub code for setting up UDP multicast • Event loop (void play())‏ • Receives Packets • Keyboard events • Timer events (EVENT_TIMEOUT) • Default is 500ms, defined in winsys.cpp

What You Need to Edit • netInit()‏ • Stub networking code in place • Most of your work will be editing play()‏ • Main event loop • Receive packets and update local state • Change local state and send packets

Protocol Design • Team creates protocol, members implement individually • At most three team members • Must be distributed • Can't have central point of failure • Over UDP Multicast • Must deal with lost packets in a reasonable way

Protocol Assumptions • Players know the UDP multicast group for the game • No cheating • One standard maze • One game per UDP multicast group • Defined as MAZEPORT in mazewar.h • To be posted on Piazza after team registration

Protocol Hints • Determine shared state • Which state is shared by which clients? • How will sufficient consistency be maintained? • Who are the readers/writers of each piece of state? • Create the protocol which will define • Syntax - clients agree on format of messages • Semantics - clients agree on meaning of messages • Timing - clients agree on timing semantics

Protocol Hints • Use network byte order(use htonl(), etc.) • When are ACKs needed? • As opposed to "fire and forget" packets • A believes he shot B. Do they need to agree? • A, B both believe they shot C. What do they do? • Joining / Exiting game • How do players discover each other? • How should failures / network congestions be handled?

Protocol Hints • There’s absolutely no globally synchronous clock • Ensure inconsistencies don't accumulate • Think about the tradeoff of the size or frequency of the packets

Protocol Example Latex: \usepackage{bytefield}

Implementation Hints • Look at the code early • Implement some local functionality, e.g. launch missile • Will help you think about your protocol • Starter code is heavily influenced by CS249 framework • Start testing interoperability ASAP • Test with simulated packet loss (commented out in starter code)

Implementation Hints • Develop/test/grade on myth clusters • ssh –X myth.stanford.edu (enable X forwarding) • If you wish to develop locally, you might encounter errors. • Try sudo apt-get install • libxaw7-dev (if missing X11/Xaw/Cardinals.h) • libx11-dev (if missing X11/stringdefs.h or X11/xlib.h)

Starter Code • ssh–X myth.stanford.edu • cd /afs/ir.stanford.edu/class/cs244b/mazewar • cp MazewarSpring2014.tar.gz ~/<your directory> • cd ~/<your directory> • tar –zxvf MazewarSpring2014.tar.gz • Develop!

Mazewar Demo

Questions? Post your questions on Piazza https://piazza.com/class#spring2014/cs244b

Assignment 1 – Mazewar Review Session