Object Sharing Over Mobile Devices

Sharad Agarwal, Ioannis MavroidisCS258

Alec WooCS294-11

2

Vision Slide• An universal infrastructure where data

can exist anywhere and be available to any device with some form of consistency guarantee

Pilot

LaptopToaster

Pilot

PilotServer

ServerNetwork

Camera

3

Why Share Over Mobile Devices

• Need collaborative applications– not for running Ocean or Barnes-Hut– distributed address book– group whiteboard / document review– group coding– collaborative control of sensors and actuators

• Need a shared data infrastructure• Can’t simply port an existing SW DSM

4

Design Requirements

• Platform independent• SW solution, in Java• Interconnection is the Internet

• Object based sharing• Data storage on remote servers

• scales {communication, capacity}• available over disconnections

• Allows disconnected operation• Emphasis on low compute power, low

bandwidth, high latency tolerance

5

System Architecture

PilotLaptop

MemoryServer

PilotWinCE Pilot

MemoryServer

Pilot

Masquerader

MemoryService

Nameserver

Internet

App Nameserver

$$ $ $ $ $

$

6

Coherence Protocol

• Directory based• SC

M

S

V

M_T

read writethru / inv

upgr / invread / wr-inv

writeback

writeback

writethru

readex

readex / inv

W_T

writethru/inv

create

destroy

7

MUD Application

• Users control characters in an arena of rooms

• move around, look, pick/drop objects, etc

• Masquerader creates shared objects• room locks, room inventory, people in room, etc

• Each client requests character init from masquerader

• When moving, linear lock ordering is used • (Dining Philosophers)

• Automated bots that run around

8

Results

XCOPILOT Min (ms) 20ms Avg (ms) 20msReadMiss 200 261ReadHit 90 129WriteThru 180 200WriteBackMiss 190 210WriteBackHit 110 134

PALM3 Min (ms) 20ms Avg (ms) 20msReadMiss 2050 2603ReadHit 800 887WriteThru 1600 1762WriteBackMiss 1500 1812WriteBackHit 700 972

Latency Measurements

Screen Shot

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Conclusions

• Formulated the need & requirements• Designed an infrastructure & application• Shown performance numbers• This was not easy

– JVMs underdeveloped– Pilot debugging infrastructure non-existent– ActiveProxy is still under development– Scalable yet versatile shared object system

is complicated