ASPECT ORIENTATED PROGRAMMING RESEARCH COMP 319 © University of Liverpool COMP319

© University of Liverpool Autonomic systems Self-Configuring systems adapt automatically to dynamically changing environments • Self-Healing systems discover, diagnose and react to disruptions • Self-Optimising systems monitor and tune resources automatically •Self-Protecting systems anticipate, detect, identify and protect themselves COMP319 © University of Liverpool

© University of Liverpool Autonomic examples Self configuring Configures maximum user count dependent on memory capacity Self healing Detects hardware loss or power down failure, transfers control to backup system Self optimising Altering cache size to improve performance Self protecting Deals with DOS service attack automatically COMP319 © University of Liverpool COMP319

More autonomic examples Optimized loading balance between servers Measures average response time Sends request to fastest server Can be optimized to load servers based on service level agreement Can use feedback from server on current memory/cpu load COMP319 © University of Liverpool

© University of Liverpool Autonomic drivers Need to automate systems management To Reduce costs Deal easily with 24/7 monitoring Be able to provide predictive management Commonly management is Partially automatic Re-active not pro-active COMP319 © University of Liverpool

© University of Liverpool Autonomic Elements Monitoring Looking for errors or trends Managing Configuring or controlling elements Reporting Auditing COMP319 © University of Liverpool

© University of Liverpool Feedback under error The first Kp is a proportional control parameter, using this on its own can lead to something called droop. Image trying to heat a furnace, by using this parameter, since as soon as the furnace reaches heat the error will be zero and the heater will switch off, at this point the heater will switch off and the temperature will droop below the target. By adding in the integral component you can try and overcome the issue of proportional bias, This component is proportional to the sum of time of all errors for a given time period. This can lead to overshoots of the target and lead to instability. Finally we have the derivation errors, this slows the change down, in this the amount of feedback is proportional to the change of error over time. This can be used to damp down the amount of correction. In general this loop has to be tuned to provide the correct control behaviour. COMP319 © University of Liverpool COMP319

© University of Liverpool AOP and Autonomics Using Dynamic Aspect-Oriented Programming to Implement an Autonomic System Greenwood and Blair Looks at Autonomics in software Dynamic aspect orientated approach Caching, security, persistence (autonomic concerns are cross also cross cut concerns) COMP319 © University of Liverpool

AOP and fault tolerance Fault tolerance AOP approach José Luis Herrero, Fernando Sánchez, Miguel Toro Page 44 AspectOrientedProgramming-Papers2001.pdf Using AOP to provide duplication of object creating and replication of object messages New language proposal JReplica COMP319 © University of Liverpool

© University of Liverpool Object Request Broker ORB New object Object handle setAttribute(handle,name,value) COMP319 © University of Liverpool

© University of Liverpool AspectJ Pointcuts for object creation initialization(ConstructorPattern) Then calls Orb for object creation Pointcuts for setting attributes set(FieldPattern) These could be use to allow for the creation of remote objects COMP319 © University of Liverpool

Fault tolerance proposal Server Object 1 Server Object 2 Client Replication layer ORB COMP319 © University of Liverpool

© University of Liverpool Summary AOP Allows the addition of transparent cross cutting concerns to complex applications Allows users to concentrate of main application logic instead of worrying about logging, duplication, persistence, security COMP319 © University of Liverpool