Real-Time CORBA Chenyang Lu CSE 520S CORBA Common Object Request - - PowerPoint PPT Presentation

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Real-Time CORBA Chenyang Lu CSE 520S CORBA Common Object Request - - PowerPoint PPT Presentation

Nov 01, 2022 49 likes •403 views

Real-Time CORBA Chenyang Lu CSE 520S CORBA Common Object Request Broker Architecture CORBA specifications q OMG is the standards body q Over 800 companies q CORBA defines interfaces , not implementations Object Request Brokers (ORB) allow

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Real-Time CORBA

Chenyang Lu

CSE 520S

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CORBA

Common Object Request Broker Architecture

Ø CORBA specifications

q OMG is the standards body q Over 800 companies q CORBA defines interfaces, not implementations

Ø Object Request Brokers (ORB) allow clients to invoke

  • perations on distributed objects transparently of

q object location q programming language q operating system q communication protocols and interconnect q hardware

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CORBA Architecture

Ø CORBA: Common Object Request Broker Architecture Ø Remote Procedure Call (RPC): Client invokes operations on objects. Ø An Object =

q An interface specified by an Interface Definition Language (IDL) q Servant(s) that implements the IDL interface

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The ACE ORB (TAO)

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Source: D.C. Schmidt, http://www.dre.vanderbilt.edu/~schmidt/TAO.html

  • Open-source

Real-Time CORBA

  • >> 1M SLOC
  • 100+ person

years of effort

  • Pioneered

R&D on DRE middleware design &

  • ptimization
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Application Example: Avionics

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  • Deterministic & statistical deadlines
  • ~20 Hz
  • Low latency & jitter
  • ~250 us
  • Periodic & aperiodic processing
  • Complex dependencies
  • Continuous platform upgrades
  • T

est flown at China Lake NAWS by Boeing OSAT II '98

  • www.cs.wustl.edu/~schmidt/TAO-boeing.html
  • Also used on SOFIA project by Raytheon
  • sofia.arc.nasa.gov
  • First use of Real-time CORBA in avionics
  • Drove Real-time CORBA standardization
  • Apply COTS & open systems to mission-critical

real-time avionics

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Application Example: Hot Rolling Mills

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  • Goals: Control the processing of molten

steel moving through a hot rolling mill in real-time

  • System Characteristics
  • Hard real-time process automation

requirements

  • i.e., 250 ms real-time cycles
  • System acquires values representing

plant’s current state, tracks material flow, calculates new settings for the rolls & devices, & submits new settings back to plant

  • Key Software Solution Characteristics
  • Affordable, flexible, & COTS
  • Product-line architecture
  • Design guided by patterns & frameworks
  • Windows NT/2000
  • Real-time CORBA
  • www.siroll.de
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Application Example: Image Processing

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  • Goals: Examine glass

bottles for defects in real-time

  • System Characteristics
  • Process 20 bottles/sec
  • ~50 ms per bottle
  • Networked configuration
  • ~10 cameras
  • Key Software Solution Characteristics
  • Affordable, flexible, & COTS
  • Embedded Linux
  • Compact PCI bus + Celeron processors
  • Remote booted by DHCP/TFTP
  • Real-time CORBA
  • www.krones.com
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RPC in CORBA

Ø CORBA: Common Object Request Broker Architecture Ø Remote Procedure Call (RPC): Client invokes operations on objects. Ø An Object =

q An interface specified by an Interface Definition Language (IDL) q Servant(s) that implements the IDL interface

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Limitations of CORBA

Ø Lacks QoS specification interfaces to applications

q Applications cannot specify rate, deadline or importance

Ø Lacks QoS enforcement

q Does not map task QoS specification to priorities of threads q Contains significant priority inversion

Ø Lacks performance optimization

q Poor worst-case and average latency

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Latencies and Priority Inversions

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The ACE ORB (TAO)

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  • Open-source

Real-Time CORBA

  • >> 1M SLOC
  • 100+ person

years of effort

  • Pioneered

R&D on DRE middleware design &

  • ptimization
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TAO Overview

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  • Based on ACE wrapper

facades & frameworks

  • Available on Unix, Win32,

MVS, QNX, VxWorks, LynxOS, VMS...

  • Thousands of users around

the world Commercially supported

http://www.dre.vanderbilt.edu/~schmidt/commer cial-support.html

Container Client

OBJ REF in args

  • peration()
  • ut args +

return

DII IDL STUBS ORB INTERFACE IDL SKEL Object Adapter ORB CORE GIOP/IIOP/ESIOPS Component (Servant)

Services

Objective: Simplify the development

  • f distributed real-time & embedded

(DRE) systems Approach: Use standard techology, patterns, & frameworks

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I/O Subsystem: Priority Inversions

Ø Messages are processed in FIFO order regardless of priorities Ø Kernel has lower priority than real-time priorities

q Processing of a high priority message in the kernel can be blocked by a

lower priority task at the application level

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I/O Subsystem: Solutions

Ø Early demultiplexing Ø Prioritized kernel processing Ø Map task priority to kernel thread Ø Note: This needs kernel support

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ORB Core: Priority Inversions

Ø Communication of different tasks shares a same socket connection. Ø Incoming requests are demultiplexed to threads in FIFO order.

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ORB Core

Priority-based Concurrency Architecture Ø Server sets model: Each priority is processed by a separate thread. Ø A separate connection is maintained for each priority in the server ORB.

q Use buffered connections to reduce run-time overhead.

Ø Suitable for fixed priority scheduling.

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Object Adapter: Problems

Ø Layered demultiplexing is inefficient in term of

q average latency q worst-case latency

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Object Adapter: Solutions

Ø Perfect hashing

q Generate a hash function offline q Computational complexity O(1)

Ø De-layered active demultiplexing

q Clients obtain index to (servant, operation) ahead of time

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Reduce Priority Inversion

Conventional ORB TAO

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Real-Time Event Service

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Limitations of RPC

Ø Tight coupling between clients and server Ø Lacks asynchronous message delivery Ø Lacks support for group communication

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Motivating Applications

Boeing Bold Stroke Middleware Infrastructure Platform

  • Operations well defined
  • Event-mediated middleware solution

Domain Company

Avionics mission computing Boeing, Raytheon Mass storage devices SUTMYN, StorTek Medical Information Systems Siemens, GE Satellite Control LMCO COMSAT Telecommunications Motorola, Lucent, Nortel, Cisco, Siemens Missile & Radar Systems LMCO Sanders, Raytheon Steel Manufacturing Siemens ATD Beverage Bottling Automation Krones AG

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CORBA Event Service

Ø Asynchronous event delivery Ø Decouples suppliers and consumers Ø Support group communication

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  • ne to many

many to one

  • ne to one

many to many

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Event Delivery Models

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Suppliers push to Event Channel, Event Channel pushes to Consumers Event Channel pulls from Suppliers, Consumers pull from Event Channel Suppliers push to Event Channel, Consumers pull from Event Channel Event Channel pulls from Suppliers, Event Channel pushes to Consumers

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CORBA Event Service Limitations

Ø Broadcasts any supplied event to all consumers Ø No filtering or correlation Ø No real-time event dispatching/scheduling Ø No periodic event

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X

X X

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TAO Real-Time Event Service

Ø Suppliers specify types of events generated. Ø Consumers subscribe to interested event types, to events from specific suppliers, or both.

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event A:S1 event B:S2 event C:S3 event B:S4

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Event Channel Architecture

Ø Push-push model for real-time delivery Ø Modularity: features are implemented in pluggable modules

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Suspend and Resume

Ø Light-weight operations to suspend/resume event delivery Ø Useful for frequent changes in consumer sets

q Mode change

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Periodic Events

Ø Consumers can register for timeout events provided by Event Service Ø Timeout events dispatched according to priority of consumer

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Event Correlation

Ø Provides event correlation

q Conjunctive (“AND”) q Disjunctive (“OR”)

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Conjunctive correlation

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Scheduling Service

Ø Separates dispatching mechanism from scheduling policy Ø Dispatcher consults run-time scheduler for priorities Ø Flexibility for different scheduling policies (e.g., RMS, EDF, MUF)

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Real-Time Event Dispatching

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Kokyu Dispatching Queue

Dispatching Thread

Kokyu Dispatching Queue Kokyu Dispatching Queue

Dispatching Thread Dispatching Thread High Priority Low Priority

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Critiques

Ø Full compatibility with CORBA

q T

  • o complex and heavy-weight for embedded systems?

Ø Centralized event channel

q Scalability for distributed systems à federated event channel q Single point of failure à fault tolerant event channel

Ø Overhead of redirection Ø Support for multicore and multiprocessor platforms.

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Federated Event Channel

Ø Gateway forwards events to remote processors.

Application Processor 1 Application Processor 2 Application Processor 3 T12 T13 T11 EC EC EC

Gateway Gateway

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Source

Ø Slides partially based on Douglas Schmidt’s TAO tutorial and Joe Hoffert’s class presentation.

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