Framework A for Environment Aware Mobile Applications
Authors: Girish Welling and B. R. Badrinath Department of computer Science Rutgers University
CIS 640 Mobile Computing presented by: Suming Chen March 4, 1998
Presentation Outline
Introduction Design Objectives Architectural Overview Event Delivery Framework q Entities l Network Aware Subsystem l l l l
q
Illustration
l Performance l Related and Future Work
Introduction
l On current system, operating system allocate resources among applications
q q
fixed resources boot-time configuration
l With a mobile computer, resources can be utilized more efficient if application is aware of changes.
q
React to changes voluntarily during execution
Introduction continue...
l The need for environment aware mobile applications:
q q q q
resource change dynamic utilization adaptation example: network application need to deal with heterogeneity of different network intermittent connectivity and changing bandwidth usually ignored above transport layer need to export link information to application
alternate network services and take advantage of changing link characteristics
Introduction continue
l So the model need to be
q q q
flexible and extensible for mobile environment aware of resource availability structured to react to changes efficiently user-level event detection separation of detection and event delivery preserve state of environment
l Approach
q q q
Connection Events Service Events
WaveLan Connectivity
Event detection Delivery policy
Connection Display
Pine: Mail/News
Event handlers
CDPD Connectivity Service Discovery
Design Objectives
l user-level detection of events l flexible, event specific delivery policies
q
separation of event detection and delivery
l integrate event notification and transfer of information associated with event l maintain current state of environment l reduce event delivery latency by thread scheduling
Architectural Overview Mobile Applications
User-level system software
High-level events
Events from user-level system modules
Environment Aware Subsystem
Primitive events from OS
Operating System
Architectural Overview continue ...
l Impact of the architecture
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Allows arbitrary types of events
such as processes communication event, monitored event, and remote event.
q q q
Flexible event delivery policy Event log Reduce delivery latency by giving hints to task scheduler combine with thread-based environment
Event Delivery Framework
l Consider the trend in operating systems
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monolithic kernel micro-kernel/single server
l Proposed: extension of micro-kernel
Event Delivery Framework continue ...
event detection delivery policy
User
kernel
Monolithic Kernel
Micro-kernel/ single server
Proposed
Event Delivery Framework continue ...
l Four classes of entities that constitute the architecture q Channels q Factories q Handlers q Event Object l In addition, an independent Registrar provides a name-service for the Channel name space
Event Delivery Framework continue ...
Event detection Delivery policy
events
Event channel
Event handlers
Event factory
Event Channel
l Binding event producers(Factories) and consumers(Handlers) q Handlers need to be registered q network channel, hardware channel, power channel l Implements delivery policy and preserves environment state q determines the delivery order of Event Objects to registered Handlers and specifies termination condition l Delivers Event Objects base on delivery policy l Hard to implement delivery policy with large number of Event Object types delivered on the same Channel l But large number of Channels could increase task overhead on the system l Preserves current state of mobile environment -- event log
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when a handler first registers with channel, Event Objects maintained in the log are delivered.
l Flexible
class Channel { Policy* policy; Event* State[MAX]; public: Channel(char* name); Channel(char* name, Policy* p); void Body(); //??? ... }; class Policy { Handler* List; ... public: void Deliver (Event*); virtual void reset(); virtual Handler* NextHandler(); virtual void AddHandler(Handler*); ... };
Event Factory
l Detect Events l Produce Event Objects
q
packages information associated with the event
l Post Event Objects through Channel l Reference of the Channel is obtained by the Registrar
Class Factory { Channel* chan; ... public: Factory(char* channelName); void PostEvent(Event*)//call ... Channel::Delivery(Event*) };
Event Handler
l An environment aware application creates a Handler bound to appropriate Channel l Reference of the Channel is obtained by the Registrar l Event Objects posted onto the Channel are delivered to the Handler l Execution of the Handler can be handled using separate thread
Class Handler { Channel* channel; ... Public: Handler (char* channelName); void Body(); ... };
Event Object Types
l Event Object types are organized as an extensible type hierarchy l Every Event Object type is a subtype of a root event l Each type is associated with a response specified in <Event_Type>::Handle() method l By default, chains the response to the immediate super-type
Event Object Types
Event
continue ...
PCMCIA
Memory
Card Insert
Card Remove
Low Memory
Memory Card Insert
Class Event { ... Public: virtual size_t Marshal(void*, size_t); virtual Event* UnMarshal(void*, size_t); ... Virtual void Handle(); };
Network Aware Subsystem
l Build a prototype implementation on i486 based laptops running MACH3.0 microkernel l C++
Connection Events Service Events
WaveLan(mhmicp) Connectivity
Event detection Delivery policy
Connection Display
Pine: Mail/News
Event handlers
CDPD(pumicp) Connectivity Service Discovery
Definition of Events
Typedef enum{up, down} LinkState; class connection: public Event { Address LocalIP; Address Gateway; LinkState State; public: Connection(Address local, Address gateway, LinkState s); }; class Services: public Event { Address Printer; Address SMTP; Address NNTP; public: Services(Address printer, Address smtp, address nntp); };
Network Channel Channel* c; main() { c = new Channel(network); c->Body(); }
Connection Event Generation (mhmicp)
Address localAddr; Factory* fact; void initialize() { /* create network factory */ fact = new Factory(network); /* initialize local data */ LocalAddr = GetMyIpAddress(); } void inCell(Address remote) { Event* e = new Connection(LocalAddr, remote, up); fact->PostEvent(e); delete e; } void lost() { Event* e = new Connection(LocalAddr, NULL, down); fact->PostEvent(e); delete e; }
Service Discovery
Handler* eh; Factory* sf; Services* NoService; Services* getServices(Address); void Connection::Handle() { //the connection event response if (State == up) sf->PostEvent(getServices(Gateway)); else if (State == down) sf->PostEvent(NoService); } main() { NoService = new Services(NULL, NULL, NULL); eh = new Handler(network); sf = new Factory(network); eh->Body(); }
Handler Code in Pine
Handler* eh; Thread* et; Connection::Handle() { //connection event response //if CDPD link // Disable full remote mailbox access, buffer outgoing mail //if WaveLan link // Enable full remote mailbox access, flush outgoing mail buffer } Services::Handle() { //service event response // change servers to those indicated in this event; } void initialize() { et = new Thread(eh = new Handler(network); }
Performance
CPU I486 I486 I486 SPARC Operation Scheme system Mach 3.0 Proposed Mach 3.0/ UX42 Linux 1.3 Solaris SunOS 5.4 Signal Signal Signal Latency 1.118 ms 0.873 ms 0.140 ms 0.174 ms
Performance continue ...
l I486 based PC running at 33 MHz vs. 110Mhz SPARC5 l SPARC5 < Linux
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large context switching time on RISC processors overhead of user-level UX server extra context switch
l UX42 < Linux
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l Ours < Mach/UX
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Performance continue ...
l Delivery latency is not significantly worse l Feasible, if enhanced
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reduce context switch overhead by provide channel abstraction as kernel primitive
l Claims that will perform better than signaling scheme when number of processors increases l Event is handled as soon as it is observed by handler thread
Related Work
l OS provide signal mechanism
q
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limited by no information related to the event can be easily delivered delivery policy is fixed and restrictive delivers synchronous events require knowledge about where exceptions occur upward flow by procedure calls or asynchronous signals
l OO PL
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l Upcalls (Swift)
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Related Work continue ...
l Reactor (ACE)
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decouple event handler from event demultiplexing vs.. event consumer from event producer push and pull vs.. pull driven by factory
l CORBA Event Services
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Future Work
l To consolidate current implementation l to develop tools to aid in the primitive utilization l to investigate how a mobile application should be structured