a generative programming approach to middleware development · middleware framework deployment...

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A Generative Programming Approach to Middleware Development

OMG Workshop on Distributed Object ComputingReal-Time And Embedded Systems, July 14-17,2003

Venkita Subramonian and Christopher GillWashington University, St. Louis

{venkita,cdgill}@cse.wustl.edu

2OMG RT and Embedded Workshop, July 2003

Scope of Component Models• Component Models for

configuring and assembling application level components

• Weaving of components done based on application characteristics

• Component configuration isolated from component development

• Some level of automation• Serves reusability of

components

Component Server

Containers Containers

FlightSchedulingProcessing

WebGateway

ComponentDeployment

&ConfigurationMechanism

Middleware Framework

Deployment&

ConfigurationMetadata

ComponentRepository

Compose Deploy

MiddlewareConfiguration Metadata 6

4

3

1234

6

Configuring and deploying an application services end-to-end

Synthesizing application component implementations

Configuring application component containers

Composing components into application server components

Synthesizing middleware-specific configurations

BusinessLogic

7

7 Synthesizing middleware implementations

ClientMiddleware Bus

CentralDataStore

1

System Development

Field RadarControl

SystemsReal-time

FlightStatusBulletinBoard

ChicagoData

Center

ComponentAssembly

FlightScheduling

2Airport

ApproachControl

5 Synthesizing dynamic QoS provisioning and adaptation logic

5


Need for Finer-level Configuration• Component configurations

– Inter-Component configuration – Intra-component configuration

• Component Implementation infrastructure

• Mapping of– High level component configurations to– Low level infrastructure elements

• Configuration of low-level infrastructure elements involve – Selection of various strategies based on

high level configurations– Validating appropriate combinations of

configurations

Component Server

Containers Containers

FlightSchedulingProcessing

WebGateway

ComponentDeployment

&ConfigurationMechanism

Middleware Framework

Deployment&

ConfigurationMetadata

ComponentRepository

Compose Deploy

MiddlewareConfiguration Metadata 6

4

3

1234

6

Configuring and deploying an application services end-to-end

Synthesizing application component implementations

Configuring application component containers

Composing components into application server components

Synthesizing middleware-specific configurations

BusinessLogic

7

7 Synthesizing middleware implementations

ClientMiddleware Bus

CentralDataStore

1

System Development

Field RadarControlSystems

Real-timeFlightStatusBulletinBoard

ChicagoData

Center

ComponentAssembly

FlightScheduling

2Airport

ApproachControl

5 Synthesizing dynamic QoS provisioning and adaptation logic

5


Static vs. Dynamic Configuration• Static configuration chosen at

system startup– compile-time decisions to improve

performance– compile-time checks based on system

properties known a priori– Inference of strategies based on high

level configurations• Reconfiguration during system

mode changes– Expensive, but more flexible and

dynamic– E.g. Factory based configurations

• Hybrid strategies – as a balance between the two

10Hz 10Hz

5Hz 5Hz

20Hz10Hz5Hz

critical

non-critical

RMS+MLF

10Hz 10Hz5Hz 5Hz

20Hz10Hz5Hz

critical

non-critical

MUF


Generative Approach as a Solution• Generative Programming

– Focus on families of software systems– Concrete system generated based on

configuration knowledge• Extend Generative programming

approach to low-level infrastructure configuration– Generate low level configurations from high

level configurations automatically• Configuration generators

– For mapping high level to low level configurations

– For assembling and weaving the right infrastructure elements

Generator

Configuration Knowledge

Concrete Implementation


C++ Template Meta-Programming• Mechanism to embed generators in C++

– Completely within the purview of C++ language• Metainformation represented using

– Member traits, Traits classes, Traits templates• Compile-time control-flow constructs

– Template metafunctions E.g. IF, THEN, ELSE, CASE– Conditional compilation based on evaluation of type-

expressions• Issues

– Advanced usage of C++ templates – Compiler support an issue


Example – RT Dispatching

Threads are all from dispatcher• Timers trigger suppliers• Suppliers push to EC• Events land in queues• Worker threads pull from queues

and push to consumers

Threads are all from dispatcher• Timers trigger suppliers• Suppliers push to EC• Events land in queues• Worker threads pull from queues

and push to consumers

Dispatcher

laxity

static

static

Prox

yProx

yFi

lterin

gC

orre

latio

n

Event Channel

ConsumersSuppliers


RT Dispatching Configuration• QoS attributes based on

scheduling policy• Bundle together all QoS

attributes in one descriptor• Can we generate the

appropriate QoS descriptor?– Use a configurator to generate the

attributes– Scheduling policy as input to

generator

QoS DescriptorGenerator

Scheduling policy

QoS Descriptor


Generator for QoS Descriptorenum Disp_Rule_t{ RMS, EDF, MLF, MUF, other };

template<Disp_Rule_t>struct QoSDesc{};//template specializationstemplate<>struct QoSDesc<RMS>{long period;//fields specific to RMS

};template<>struct QoSDesc<EDF>{long deadline;//fields specific to EDF

};template<>struct QoSDesc<MLF>{//fields specific to MLF

};

template <Disp_Rule_t disp_rule>struct QoSDescriptorGenerator{typedef typename

CASE<EDF,QoSDesc<EDF>,CASE<RMS,QoSDesc<RMS>,CASE<MLF,QoSDesc<MLF> > > >

disp_rule_case_list;

typedef typenameSWITCH<disp_rule,

disp_rule_case_list>::RET QoSDescriptor_;

typedef QoSDescriptor_ RET;};

typedefQoSDescriptorGenerator<EDF>::RET

QoSDescriptor;


Other Use-Cases• ORB Infrastructure

configuration– Strategies based on inference

from system properties• E.g. Strategy used to wait for

replies – Wait on connection

• No interleaved processing of incoming requests

• No blocking factor– Wait on reactive mechanism

• Interleaved processing of incoming requests

• Blocking factor needs to be considered

• Configurator to choose strategy based on system characteristics

Client ServerC

Reactor

wait

Reactor

Servant

Callback6

Deadlockavoided

by waitingon reactor

1

3

42

5

Client ServerC

Reactor

3 wait

Reactor

Servant

Deadlockhere

Callback

1 2 4

5

Nested Upcall scenario


Related Work• RMA using template meta programming

– RMA schedulability analysis at compile-time within the C++ type system

– Compile error when utilization bound exceeds the RM utilization bound

– “Rate-Monotonic Analysis in the C++ Typesystem”, Deters, Gill and Cytron, presented at RTAS 2003 Workshop on Model-Driven Embedded Systems

• Task-Scheduler Logic– Work by John Regehr and Alastair Reid– Reasoning about Concurrency in Component-Based

Systems Software– First order logic for representing system knowledge


Conclusions• Component models deal with higher level

application components• Need to map high level specifications to

configuration of finer-grained components• Extend generative programming to configuration

of fine-grained infrastructure• Algebraic specification of system behavior • Inference of infrastructure configuration

strategies by reasoning of system behavior

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