Rob Spoor

1
Design of a Real-Time Distributed Shared Data
Space
AKA Real-time GSpace

• Rob Spoor

2
Introduction

• Shared Data Space
• GSpace
• RGSpace Issues
• CORBA / TAO
• RGSpace Architecture
• Scheduling
• RGSpace Global Design
• Conclusion

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Shared Data Space Model
Model Overview
A
B
C
actions read, put, take
shared data space
tuple ordered sequence of typed fields with
specified values
(str name, int age) - put ((Rob, 25))
template ordered sequence of typed fields with
or without a specified value
(str name, int age) - read ((Rob, int ?)), take
((str ?, 25))
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Shared Data Space Features

• Uncoupling in time no need to be online at the
  same time
• Uncoupling in space no need to know each other,
  only the data
• Computation is separated from coordination

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GSpace Overview
application
6
Separating Concerns in GSpace
mapping
Implementation
Specification
Distribution Policy Descriptor
downloading
7
GSpace Kernel Structure
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Real-time GSpace RGSpace

• Add timing constraints to actions
• Focus on predictability, not performance

9
Separating Concerns in RGSpace
mapping
Implementation
Specification
Distribution Policy Descriptor
downloading
10
Examples of Timing Constraints

• read((Rob, int ?)) must be finished within 15ms
• put((temperature)) will occur every 100ms, and
  must be finished within 10ms

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Examples of Policies for Handling Timing Errors

• Reschedule to fit
• Reject new task
• Shut down RGSpace
• ???

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Real-time CORBA TAO

• TAO The ACE ORB
• TAO Subsystems
• I/O Subsystem
• Run-time Scheduler
• ORB Core
• Object Adapter
• Stubs and Skeletons
• Memory Manager
• QoS API

13
TAO ORB Architecture
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RGSpace Kernel Structure
Application Component
RGSpace
Kernel
download
15
RGSpace Kernel Flow of Control
Application Component
RGSpace
Kernel
Controller
download
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RGSpace Processes / Threads
Thread Pool
Incoming requests
Controller
Application
other OS tasks
RGSpace Kernel Scheduler
Acceptance test
Scheduling policy
OS Scheduler
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RGSpace Design Decisions

• Limit to periodic actions
• Use rate monotonic / deadline monotonic
• Limit the size of the data space

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Accepting an Action
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Denying an Action
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Handling an Action
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Intermediate Conclusions

• Scheduling
• Real-time CORBA
• Real-time OS
• Real-time networking
• Real-time JAVA
• Real-time (distributed) databases

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Plans for Completing this Project

• Implement for one machine only (no network)
• Extend for multiple machines (networked)
• Write my report
• ???

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Questions?