1 5/30/98lcr ‘98 bbn technologies qos aspect languages and their runtime integration joseph p....

1 5/30/98 LCR ‘98 BBN Technologies

QoS Aspect Languages and their Runtime Integration

Joseph P. Loyall, David E. Bakken, Richard E. Schantz, John A. Zinky, David A. Karr, and Rodrigo Vanegas

BBN Technologies/GTE InternetworkingCambridge, Massachusetts, USA

http://www.dist-systems.bbn.com/tech/QuO/

Fourth Workshop on Languages, Compilers, and Run-time Systems for Scalable Computers (LCR98)

May 28-30, 1998

Carnegie Mellon University, Pittsburgh, Pennsylvania, USA


Many distributed systems have critical QoS requirements, e.g., real-time performance, fault tolerance, or dependability

CINCJ2

CINC OperationsPlanning Group

OPS/ INTELWORKSTATION

TARGET

CJTFPlanners

TARGET

MissionsCenters of GravityTask refinementForces refinementPhases refinementCOA evaluationCOA selection

FLTCINC MaritimePlanning Center

TMS CASES & HPC

Maritime & AirCampaign Assessment

JOINT FORCE MARITIMECOMPONENT CMDR

CASES TARGET

Task refinementIntegrated Target PrioritiesForces refinementSchedule refinementCOA evaluation

JOINT FORCE AIRCOMPONENT CMDR

TARGET ACPT

IDB

MissionsCOAsStrategy

Crisisassessment

COA evalCOA eval AirMar

XIDB

Target Nomination ListMaster Attack PlanAttack Plan Status

JFACCCombat Ops

Target Nomination ListWeaponeering

XIDB

APS/FLEX

TAMPS/COMPASS

JMCISIDB

Air Tasking Order (ATO)

NATOOPS/INTELWORKSTATION

Rear-echelonSim Center

toSHAPE

MasterTargetList

APS/FLEX RAAP

Refinement& eval

collaborative development

rehearse

Refinement& eval

ATO

Target data / Weaponeering


Distributed object middleware has emerged to solve heterogeneity and distribution problems

Middleware makes programming distributed applications easier

• Standard programming interfaces hide platform and system dependencies

• Standard protocols, e.g., message formats, allow applications on different systems to interoperate

• Middleware provides higher level, application oriented programming building blocks

Host 2

Impl

Host 1

Impl

Applications

Host 2

Simulation

Distributed ObjectMiddleware

Impl

IDLIDL

CollaborativePlanning

IDL

Hosts/Systems

Workflow


Wide-area distributed applications are (still) hard to build and maintain

Current object-oriented middleware is not sufficiently transparent with respect to real-time, fault tolerance, and other non-functional issues, and does not sufficiently accommodate adaptive behavior• WANs are unpredictable, dynamic environments

• Configuration for application changes over time

• Performance and system properties are buried under IDL’s functional interface, so one can’t easilyhelp application adapt to changing environment

reuse code for a new environment

• Programmers end up programming around the middleware to achieve real-time performance, predictability, security, etc.

Host1

Client1

Host2

Client2

Host4

Client3

ObjectResource Constrained

Wide Area Network LANHost3

Client4


Distributed object middleware with QoS extensions is a powerful abstraction layer on which to build applications

Ethernet

TCP/IP QoS

ATM

RSVP

Multicast

Collaborative Planning

WorkFlow

SimulationApplications for geographically dispersed, heterogeneous environments

Distributed objects are the first abstraction layer that unifies CPU, storage, and communications

This interface needs to be hidden from applications

• It is too complicated• It is changing too quickly

CORBA + QuO


System condition objects monitor QoS in the system

• system condition objects recognize changes in the system and notify the contracts that observe them

• QuO contracts notify client programs, users, managers, and other system condition objects through transition behavior

SystemCondition Objects

QuO applications specify, control, monitor, and adapt to QoS in the system

Application

Alternate Implementations

Contract (operating regions)

Servers

Network

ORB

Replication Mgr

Resource ReservationManager

IDS

Specification of operating regions, alternate implementations, and adaptation strategies using QuO’s QDL

Multiple layers of adaptation• managers and mechanisms can

adapt to changes in the system• QuO contracts provide another

layer of adaptation• Client and user can also adapt

Mechanisms and managers control QoS in the system

• a layer below QuO that provides ORB-level services, such as managed communi-cation, replication, or security

• contracts and delegates interface to these services through system condition objects


The QuO designer provides contracts, system condition objects, and delegates in the application

• Contracts summarize the possible states of QoS in the system and behavior to trigger when QoS changes– Regions can be nested, representing different epochs at which QoS information becomes available, e.g., negotiated regions represent the levels of service a client expects to receive and a server expects to provide,

while reality regions represent observed levels of service

– Regions are defined by predicates over system condition objects

– Transitions specify behavior to trigger when the active regions change

• System condition objects are used to measure and control QoS– Provide interfaces to system resources, client and object expectations, mechanisms, managers, and specialized ORB functions

– Changes in system condition objects observed by contracts can cause region transitions

– Methods on system condition objects can be used to access QoS controls provided by resources, mechanisms, managers, and ORBs

• Delegates provide local state for remote objects– Upon method call/return, delegate can check the current contract state and choose behavior based upon the current state of QoS

– For example, delegate can choose between alternate methods, alternate remote object bindings, perform local processing of data, or simply pass the method call or return through


QuO adds QoS control and measurement into the DOC remote method call

Client Network Server

ApplicationDeveloper

Qosketeer

MechanismDeveloper

Logical Method Call Client

Delegate

ORB Proxy

Specialized ORB

ContractSysCond

SysCond

SysCond SysCond

Object

Delegate

ORB Proxy

Specialized ORB

Contract

Network

Mechanism/PropertyManager

SysCond

SysCond

SysCond


Major components of the QuO framework• Quality Description Languages (QDL)

– Analogous to CORBA’s Interface Description Language (IDL)

– Support the specification of QoS contracts

delegates and their adaptive behaviors

connection, creation, and initialization of QuO application components

– QuO includes code generators that parse QDL descriptions and generates Java and C++ code for contracts, delegates, creation, and initialization

• QuO Runtime Kernel– Contract evaluator

– Factory object which instantiates contract and system condition objects

• System Condition Objects– Implemented as CORBA objects

– We have a growing library of system condition objects for reuse


Overview of the QuO architecture

SystemConditions

QuO Runtime System(Java)

Application (C++ or Java)

FunctionalDelegate (C++ or Java)

premethod

postmethod

set client expectation

ORB set object expectation

system event

Contract


Client

Client CodeReference

Delegate

Proxy

Connect Callback

Factory

QuO Kernel

Syscond Syscond

ORB

Contract

Network Control Manager

QuO Kernel

Contract

SC SC

ORB

ORBProxyProxy

Object

1) Client calls delegate

2) Delegate evaluates contract

3) Measurement system conditions are signaled

4) Contract snapshots value of system conditions

5) Contract is re-evaluated

6) Region transitions trigger callbacks

7) Current region is returned

8) If QoS is acceptable, delegate passes the call to the remote object

9) Remote object returns value

10) Contract is re-evaluated...

11) Return value given to client

1

38

112

7

4

5

6

10

Del.

9

Client calls delegate, which triggers contract evaluation and chooses behavior based upon current regions


Overview of Aspect-Oriented Programming

• A program is decomposed functionally into modules, objects, procedures, etc. as usual

• Aspects are programmed separately in special purpose languages– Aspects cross-cut the functional components

– Traditionally are programmed by inserting code in many modules, throughout the system, resulting in a tangled mess of code

– Examples of aspects are synchronization, instrumentation, data structure, QoS

• Code generators weave aspects into the functional modules


AOP enables separation of concerns

class Book { private BookID id; private PostScript ps; private UserID borrower;

public Book(String t, String a, String i, PostScript p) { id = new BookID(t,a,i); ps = p; }

public UserID get_borrower() {return borrower;} public void set_borrower(UserID u) {borrower = u;} public PostScript get_ps() { return ps; } public BookID get_bid() { return id; }}

class BookID { private String title; private String author; private String isbn;

public BookID(String t, String a, String i) { title = t; author = a; isbn = i; } public String get_title() {return title;}}

class User { private UserID id; Library theLibrary; Printer thePrinter;

public User(String n) { id = new UserID(n); }

public boolean getBook (String title) { BookID aBook=null; try{ aBook = theLibrary.getBook(id, title); } catch (RemoteException e) {} try { thePrinter.print(id, aBook); } catch (RemoteException e) {} return true; } public UserID get_uid() { return id; }}

class UserID { private String name;

public UserID(String n) { name = n; } public String get_name() { return name; }}

interface LibraryInterface extends Remote { public BookID getBook(UserID u, String title) throws RemoteException;

public PostScript getBookPS(BookID bid) throws RemoteException;}

class Library extends UnicastRemoteObject implements LibraryInterface { Hashtable books; Library() throws RemoteException { books = new Hashtable(100); } public BookID getBook(UserID u, String title) throws RemoteException { System.out.println("REQUEST TO GET BOOK " + title); if(books.containsKey(title)) { Book b = (Book)books.get(title); System.out.println("getBook: Found it:" + b); if (b != null) { if (b.get_borrower() == null) b.set_borrower(u); return b.get_bid(); } } return null; } public PostScript getBookPS(BookID bid) throws RemoteException { if (books.containsKey(bid.get_title())) { Book b = (Book)books.get(bid.get_title()); if (b != null) return b.get_ps(); } return null; }

}

interface PrinterInterface extends Remote { public boolean print (UserID u, BookID b) throws RemoteException;}

public class Printer extends UnicastRemoteObject implements PrinterInterface { private Vector jobs = new Vector(10, 10); private Library theLibrary;

public Printer() throws RemoteException{} public boolean print (UserID u, BookID b) throws RemoteException{ PostScript ps=null; try{ ps = theLibrary.getBookPS(b); } catch (RemoteException e) {} Job newJob = new Job (ps, u); return queue(newJob); } boolean queue(Job j) { //... return true; }}

“weaver”

public class PrinterImpl { String status = “Idle” Vector jobs;

public PrinterImpl() {} pubilc get_status() { return status } public add_job(int j) { jobs.add(j); }}

class Library { Hashtable books; Library(){ books = new Hashtable(100); } public Book getBook(User u, String title) { System.out.println("REQUEST TO GET BOOK " + title); if(books.containsKey(title)) { Book b = (Book)books.get(title); System.out.println("getBook: Found it:" + b); if (b != null) { if (b.get_borrower() == null) b.set_borrower(u); return b; } } return null; }}

class User { private String name; Library theLibrary; Printer the; Printer

public User(String n) { name = n; }

public boolean getBook (String title) { Book aBook = theLibrary.getBook(this, title); thePrinter.print(this,aBook); return true; }}

class Book { private String title; private String author; private String isbn; private PostScript ps; private User borrower;

public Book(String t, String a, String i, PostScript p) { title = t; author = a; isbn = i; ps = p; }

public User get_borrower() {return borrower;} public void set_borrower(User u) {borrower = u;} public PostScript get_ps() { return ps; }}

portal Printer { void print(Book book) { book: Book: {direct pages;}

}

portal Library { Book find (String title){ return: Book: {copy title, author, isbn;} }}

4 classes

2 aspects

class Book { private BookID id; private PostScript ps; private UserID borrower;

public Book(String t, String a, String i, PostScript p) { id = new BookID(t,a,i); ps = p; }

public UserID get_borrower() {return borrower;} public void set_borrower(UserID u) {borrower = u;} public PostScript get_ps() { return ps; } public BookID get_bid() { return id; }}

class BookID { private String title; private String author; private String isbn;

public BookID(String t, String a, String i) { title = t; author = a; isbn = i; } public String get_title() {return title;}}

class User { private UserID id; Library theLibrary; Printer thePrinter;

public User(String n) { id = new UserID(n); }

public boolean getBook (String title) { BookID aBook=null; try{ aBook = theLibrary.getBook(id, title); } catch (RemoteException e) {} try { thePrinter.print(id, aBook); } catch (RemoteException e) {} return true; } public UserID get_uid() { return id; }}

class UserID { private String name;

public UserID(String n) { name = n; } public String get_name() { return name; }}

interface LibraryInterface extends Remote { public BookID getBook(UserID u, String title) throws RemoteException;

public PostScript getBookPS(BookID bid) throws RemoteException;}

class Library extends UnicastRemoteObject implements LibraryInterface { Hashtable books; Library() throws RemoteException { books = new Hashtable(100); } public BookID getBook(UserID u, String title) throws RemoteException { System.out.println("REQUEST TO GET BOOK " + title); if(books.containsKey(title)) { Book b = (Book)books.get(title); System.out.println("getBook: Found it:" + b); if (b != null) { if (b.get_borrower() == null) b.set_borrower(u); return b.get_bid(); } } return null; } public PostScript getBookPS(BookID bid) throws RemoteException { if (books.containsKey(bid.get_title())) { Book b = (Book)books.get(bid.get_title()); if (b != null) return b.get_ps(); } return null; }

}

interface PrinterInterface extends Remote { public boolean print (UserID u, BookID b) throws RemoteException;}

public class Printer extends UnicastRemoteObject implements PrinterInterface { private Vector jobs = new Vector(10, 10); private Library theLibrary;

public Printer() throws RemoteException{} public boolean print (UserID u, BookID b) throws RemoteException{ PostScript ps=null; try{ ps = theLibrary.getBookPS(b); } catch (RemoteException e) {} Job newJob = new Job (ps, u); return queue(newJob); } boolean queue(Job j) { //... return true; }}

• Traditional: Code to handle different data representations is tangled throughout the classes

• Aspect-oriented: Program is divided into classes and aspects; a code weaver puts them together

Figures copyright 1997, 1998 Xerox Corporation


QuO’s aspect languages, aka Quality Description Languages (QDL)

• Contract Description Language (CDL) – expected regions of QoS

– reality regions of QoS

– transitions for adapting to changing levels of service

• Structure Description Language (SDL) – behavior alternatives for remote objects and their delegates

– alternate bindings and connection strategies

• Resource Description Language (RDL) – available system resources and their status

Implementation

CDL SDL RDL

QDLIDL

QDL + IDLCompiler

QuOapplication

QuO Runtime

ORB


Measured capacity >= 10

As_expected:

Insufficient_resources:Measured capacity < 10

Contracts summarize system conditions into negotiated and reality regions and define transitions between them• Negotiated regions represent the expected behavior of client and server objects, and reality regions represent observed system behaviors

• Predicates using system condition objects determine which regions are valid

• Transitions occur when a region becomes invalid and another becomes valid

• Transitions might trigger adaptation by the client, object, ORB, or system

Normal:Expected capacity >= 10

Degraded:Expected capacity < 10Expected capacity >= 2

As_expected:

Extra_resources:

Measured capacity < 10Measured capacity >= 2

Measured capacity < 2Insufficient_resources:


Unusable:Expected capacity < 2

As_expected:

Extra_resources:

Measured capacity < 2


= Expected Region

= Reality Region


Quality Description Languages for specifying operating regions and adaptive behaviors

CORBA IDLtypedef sequence<long> LongSeq;interface Targeting { long calculate_distance_to_target(in long xcoord, in long ycoord); long identify_target(in long xcoord, in long ycoord);};

CodeGenerators

CodeGenerators

contract Replication( object client, object server ) is ... negotiated regions are region Low_Cost : ... region Available : when client.expectations.requested > 1 => reality regions are region Too_Low : when measured <= 1 => region Normal : when measured > 1 => transitions are transition any->Too_Low : client.callbacks.availability_degraded(); transition any->Normal : client.callbacks.availability_back_to_normal(); ... transitions are ...end Replication;

delegate behavior for Targeting and repl_contract is obj : bind Targeting with name SingleTargetingObject; group : bind Targeting with characteristics { Replicated = True };

call calculate_distance_to_target : region Available.Normal : pass to group; region Low_Cost.Normal : pass to obj; region Available.TooLow : throw AvailabilityDegraded; return calculate_distance_to_target : pass_through; default : pass_throughend delegate behavior; SDL

QuO RuntimeQuO Runtime

ContractDelegate

CDL


CDL contract to control object replicationcontract Replication( object client, object server ) is var measured : measured_replication init(); negotiated regions are region Low_Cost : when client.expectations.requested == 1 => reality regions are region Too_Low : when measured == 0 => region Normal : when measured == 1 => region Too_High : when measured > 1 => transitions are transition any->Too_Low : client.callbacks.availability_degraded(); transition any->Normal : client.callbacks.availability_back_to_normal(); end transitions; end reality regions; region High_Avail : when client.expectations.requested > 1 => reality regions are region Too_Low : when measured <= 1 => region Normal : when measured > 1 => transitions are transition any->Too_Low : client.callbacks.availability_degraded(); transition any->Normal : client.callbacks.availability_back_to_normal(); end transitions; end reality regions; transitions are transition Low_Cost->High_Avail : adjust_degree_of_replication(client.expectations.requested); transition High_Avail->Low_Cost : adjust_degree_of_replication(client.expectations.requested); end transitions; end negotiated regions;end Replication;


SDL code that supports choosing between replicated and non-replicated server objects

delegate behavior for Targeting and repl_contract is

obj : bind Targeting with name SingleTargetingObject;

group : bind Targeting with characteristics { Replicated = True };

call calculate_distance_to_target :

region Available.Normal :

pass to group;

region Low_Cost.Normal :

pass to obj;

region Available.TooLow :

throw AvailabilityDegraded;

return calculate_distance_to_target :

pass_through;

default : pass_through

end delegate behavior;

• SDL supports choosing between objects, choosing between methods, run-time binding, exceptions, and embedded Java or C++ code.


Status of QuO

• QuO version 0.5 (internal release only) done, including the QuO kernel; two aspect languages, CDL and SDL, and their code generators, i.e., weavers; and a small library of system condition objects

• Currently working on two prototype applications of QuO– AQuA, which addresses availability through object replication

– DIRM, which addresses managed communication through resource reservation

• Continuing development of the QuO framework– Multiple contracts, layering of delegates, contracts on the client and the server side

– Further SDL development, including connection generation, and RDL

– More example applications, libraries of system condition objects

1 5/30/98lcr ‘98 bbn technologies qos aspect languages and their runtime integration joseph p....

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