PolyORBVersatile Middleware forInteroperable Critical Systems

PolyORBVersatile Middleware forInteroperable Critical Systems

Presentation cover page EU

www.adacore.com

Slide: 2

Overview

• Distributed programming paradigms

• Distribution models and middleware

• Example

• Pros and Cons of current models

• PolyORB, a versatile middleware

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Distributed Programming Paradigms

Slide: 4

Programming Distributed Systems

• Ad-hoc communication (e.g. via sockets)

• Message passing

• Remote procedure calls (RPCs)

• Distributed objects

• Shared memory

Slide: 5

Where It All Started: Sockets

Send (…, Bytes); Receive (…, & Bytes [ ]);

Slide: 6

Send bytes

Open socket

Get bytes

Open socket

Send bytes

Close socket

Get bytes

raw bytesraw bytes

raw bytesraw bytes

time time

Slide: 7

Problems with Ad-Hoc Communication

• No interfaces– Low-level programming

– Less reusable, portable, configurable

– Error prone

• Does not lead itself to formal proofs

• Things like sockets exchange bytes– How do you exchange more complex data structures ?

– How do you handle heterogeneous systems ?

• You need to marshall / unmarshall your data

Slide: 8

Message Passing

• Automatically marshall / unmarshall data transmitted

• Not transparent – partitioning explicit in the code

• Coordinating message sending / receiving can be

complex

• Hard to do fault-tollerance in the asynchronous model

• Can be a good model for RT systems– Asynchronous message passing does not affect scheduling

Slide: 9

time time

function Foo (X: Integer) return Float is … return …;end Foo;

Result := Foo (Param)

Result := Foo (Param)

Send ParametersSend Parameters

Send ResultSend Result

Remote Procedure CallRemote Procedure Call

Slide: 10

RPCs: A Higher Level Programming Paradigm

• RPC handled by the middleware

• Parameters and results passed across the network without programmer intervention

• Heterogeneity handled transparently

• The fact that the RPC is remote can be hidden– Ada 95 DSA & Java RMI

• Synchronous (and even asynchronous) RPCs can create problems for RT systems

– Priority inversion problem …

Slide: 11

Distributed Objects

• Distributed objects = RPCs in the OO world

• RPCs handling inheritance & polymorphism

Slide: 12

A Simple Comparison

Object-OrientedObject-OrientedProgrammingProgramming

Object-OrientedObject-OrientedProgrammingProgramming

Programming withGOTOs

Programming withGOTOs

StructuredProgramming

StructuredProgramming

Distributed ObjectsDistributed ObjectsDistributed ObjectsDistributed Objects

Message passing(sockets)

Message passing(sockets)

RPCsRPCs

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Distributed Models and Middleware

Slide: 14

Current Models

• Seamless integration with the programming language– Ada 95 DSA (Distributed Systems Annex)

– Java RMI (Remote Method Invocation)

• Language-independent / vendor-independent– CORBA

• Language-independent / vendor-dependent– WSDL/SOAP (more of a protocol with an IDL on top)

• …

Slide: 15

Where is the Magic?

Result := Foo (Param);

function Foo (X: Integer) return Float is … return …;end Foo;

Slide: 16

The Magic

Result := Foo (Param);

function Foo (X: Integer) return Float is return …;end Foo;

Middleware

stub

unmarshall results

marshall parameters

receive

send

Middleware

skeleton

unmarshall parameters

marshall results

receive

send

Interface

Slide: 17

Defining the Terms

• Middleware– Local client / server libraries to send /

receive distant requests

• Interface– The interface of the distributed

services exported by the server

• Transport protocol– The protocol used to code and

transport the data between clients and servers

• Client stub:– Marshals the parameters

– Sends the request over the network

– Waits for the response

– Unmarshals the result and delivers it to the client

• Server skeleton:– Receives the request

– Unmarshals the parameters

– Selects and calls the appropriate subprogram

– Marshals the result and sends the response

Sectional cover- Two guys working together

An example

Slide: 19

An Example

• Simple example of how the 3 models work– CORBA

– WSDL/SOAP

– Ada 95 DSA (Distributed Systems Annex)

• We only show (in red) the code written by the programmer

– i.e. the code the programmer is forced to write in a given model

• We do not show the code that is generated automatically

Slide: 20

The Starting Point

package Types istype Sensor is …;type Temperature is …;

end Types;

package Types istype Sensor is …;type Temperature is …;

end Types;

with Types; use Types;with Device;procedure Client is

S : Sensor := …;T : Temperature := Device.Get_T (S);…

end Client;

with Types; use Types;with Device;procedure Client is

S : Sensor := …;T : Temperature := Device.Get_T (S);…

end Client;

with Types; use Types;package Device is

function Get_T (S : Sensor) return Temperature;

end Device;

with Types; use Types;package Device is

function Get_T (S : Sensor) return Temperature;

end Device;

package body Device isfunction Get_T (S : Sensor)

return Temperatureis

…end Get_T;

end Device;

package body Device isfunction Get_T (S : Sensor)

return Temperatureis

…end Get_T;

end Device;

Slide: 21

The Objective

package Types istype Sensor is …;type Temperature is …;

end Types;

package Types istype Sensor is …;type Temperature is …;

end Types;

Node 1Node 1

with Types; use Types;with Device;procedure Client is

S : Sensor := …;T : Temperature := Device.Get_T (S);…

end Client;

Node 2Node 2

with Types; use Types;package Device is

function Get_T (S : Sensor) return Temperature;

end Device;

package body Device isfunction Get_T (S : Sensor)

return Temperatureis

…end Get_T;

end Device;

Slide: 22

CORBA: The IDL

module Types { typedef … Sensor; typedef … Temperature;};

#include "types.idl"

interface Device { Types::Temperature Get_T (in Types::Sensor s);};

Slide: 23

Corba: Updated Packageswith CORBA;package Types is

type Sensor is new CORBA.…;type Temperature is new CORBA.…;

end Types;

with CORBA;package Types is

type Sensor is new CORBA.…;type Temperature is new CORBA.…;

end Types;

Node 1Node 1

with Types; use Types;with Device;procedure Client is

S : Sensor := …;T : Temperature;D_Ref : Device.Ref;

beginCORBA.ORB.Initialize ("ORB");-- Getting the distant CORBA.ObjectCORBA.ORB.String_To_Object (..., D_Ref);T := Device.Get_T (D_Ref, S);…

end Client;

Node 2Node 2

with Types; use Types;with PortableServer;package Device.Impl is

type Object is new … with null record; ...

function Get_T (Self: access Object; S : Sensor) return Temperature;

end Device.Impl;

package body Device.Impl isfunction Get_T

(Self: access Object; S : Sensor) return Temperature is…

end Get_T;end Device.Impl;

Slide: 24

SOAP (with AWS – the Ada Web Server)

ClientClientwith Types; use Types;with Device_Service.Client;procedure Client is

S : Sensor := …;T : Temperature :=

Device_Service.Client.Get_T (S);…

end Client;

unchanged

unchangedServerServer

unchangedunchanged

package Server isfunction Soap_CB (…) return …;

end Server;

package body Server isfunction Soap_CB (…) return … is

if SOAPAction = "Get_T" then return … wrapped Get_T call ... end if;

end Soap_CB;end Server;

Slide: 25

Ada 95 DSA

package Types ispragma Puretype Sensor is …;type Temperature is …;

end Types;

package Types ispragma Puretype Sensor is …;type Temperature is …;

end Types;

ClientClient

ServerServer

with Types; use Types;package Device is

pragma Remote_Call_Interface;

function Get_T (S : Sensor) return Temperature;

end Device;

unchanged

unchanged

unchanged

unchanged

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Pros and Cons of Current Models

Slide: 27

Language independent

Vendor independent

from the

programmer point of view

Partitioning

distributing services on machines

IDL IDL to language mappings

Transport Protocol

Ada 95 DSA Java RMI

NO YESTransparent in the code

The language

itselfIdentity

Vendor dependent

CORBA YES YESExplicit in the code

OMG IDL Standardized Standardized

SOAP YES NOExplicit in the code

WSDLVendor

dependentStandardized

Slide: 28

Ada 95 DSA Java RMI

CORBA

SOAP

Node 1 Code

Middleware ProtocolProtocol

Node 2 Code

Middleware

Standardized

Vendor specificVendor specific

Standardized

Standardized

GIOPGIOP

Standardized

Vendor specific

SOAPSOAP

Vendor specific

Interface

Ada/Java

IDL

WSDL

Slide: 29

PROS CONS

Ada 95 DSA Java RMI

Programmers have a very small learning curve

Distribution not hardcoded

Same language for all the nodes

Stuck with 1 vendor

CORBA

Many things standardized

Language independence

Vendor independence

Very steep learning curve for programmers

Distribution hard coded

SOAPReuses web servers infrastructure (firewalls, web servers, …)

Learning curve for programmers

Strong web service orientation

Stuck with 1 vendor

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PolyORB – Connecting models

Slide: 31

Application and Protocol Personalities

Can we mix programming models and protocols?

• Yes with multiple cooperating personalities

Programming Modelapp personality

Middleware Protocolprotocol personality

Programming Modelapp personality

Middleware

Slide: 32

PolyORB – Colocated, cooperating personalities

With PolyORB you can mix and match

• Application and protocol personalities

app personality A

PolyORB

app personality B

PolyORB

app personality A

protocol personality C

app personality B

protocol personality C

protocol personality C

Slide: 33

PolyORB is Interoperable (1 of 2)

app personality A

PolyORBprotocol

personality B

app personality B

Other Middleware

app personality A

protocol personality B

Slide: 34

PolyORB is Interoperable (2 of 2)

app personality A

OtherMiddleware

protocol personality A

app personality B

PolyORBprotocol personality A

app personality B

Slide: 35

PolyORB as a Bridge

app personality A

Middleware A

app personality C

PolyORBPolyORBapp personality B

Middleware B

Protocol B

protocol A protocol B

app personality C

Prot

ocol

A

Slide: 36

Standardized Code and Protocol Personalities

• Standardized Ada code personalities– Ada 95 DSA (Distributed System Annex)

– Ada 95 CORBA

• Standardized protocols– CORBA GIOP

– SOAP

• PolyORB supports all 4 combinations

Slide: 37

Ada DSA and CORBA

Ada DSA and SOAP

Ada CORBA and CORBA

Ada CORBA and SOAP

Ada DSA

PolyORB GIOPGIOP

CORBA app

ORB

Ada DSA

PolyORB SOAPSOAP

SOAP app

Ada CORBA

PolyORB GIOPGIOP

CORBA app

ORB

Ada CORBA

PolyORB SOAPSOAP

SOAP app

38

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PolyORB – High Integrity middleware

Slide: 39

PolyORB – Adapting to the application

• Configurable and scalable

• Can change scheduling model/policy

• Can be configured to be deterministic

• Allows you to reuse code written for different distribution models

Slide: 40

PolyORB – Adapting to the operating environment

• Multiple tasking profiles:full tasking, Ravenscar-only, or no tasking

• Can configure memory management policy

• Multiple transport mechanisms

Slide: 41

PolyORB – Formally proven distribution kernel

• Modular architecture isolating primitive modules

• Identified behavioural properties for each core module

• Colored Petri net modelization of μBroker

• Formal validation by model reduction and model checking

– 10**17 states…

– … verified in 36 hours on a 3.4 GHz Pentium IV / 3 Gb of RAM

Slide: 42

Summary: PolyORB – Versatile middleware

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The interoperable, configurable middleware for critical applications

The interoperable, configurable middleware for critical applications