Real-time Software Design

Real-time Software Design

Design Patterns for Real-Time Systems Guide Faculty Mrs. Barkha Vijh Presented By; kaushik

Mayank

Introduction 

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A Design Pattern is a general reusable solution to a commonly occurring problem in software design.[1] A Distributed Computing System is a method of computer processing in which different parts of a program run simultaneously on two or more computers that are communicating with each other over a network. [2] A Real-Time Computing System is the study of hardware and software systems which are subject to a "real-time constraint“.[3]

Real-Time System Design Pattern It’s a reusable solution that can be applied either A Distributed System or A Real-Time System

Active Object 

Intent “Decouples method execution from method invocation to enhance concurrency and simplify synchronized access to an object that resides in its own thread of control. “ [4] This design pattern may also be referred to as Concurrent Object and Actor

Architectural considerations 

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Because of the need to respond to timing demands made by different stimuli/responses, the system architecture must allow for fast switching between stimulus handlers. Timing demands of different stimuli are different so a simple sequential loop is not usually adequate. Real-time systems are therefore usually designed as cooperating processes with a real-time executive controlling these processes.

Active Object Design Pattern Example - Restaurant 

Customer -> Client

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Waiter -> Proxy

Active Object Design Pattern Example - Restaurant 

Manager -> Scheduler

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Order Queue -> Activation Queue

Active Object Design Pattern Example - Restaurant 

Order -> Method Request

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Servant -> Chef

Active Object Design Pattern Consequences 

Pro’s • • •

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Enhances concurrency Simplifies synchronization Method execution order can differ from invocation order

Con’s

• Performance overhead • Hard to debug

R-T systems design process Design algorithms to process each class of stimulus and response. These must meet the given timing requirements. Design a scheduling system which will ensure that processes arestarted in time to meet their deadlines. Integrate using a real-time operating system. 

Active Object Design Pattern Known Uses CORBA ORBs  ACE Framework  Siemens MedCom  Siemens Call Center management system  Actors 

Monitor Object 

Intent “The Monitor Object pattern synchronizes method execution to ensure only one method runs within an object at a time. It also allows an object’s methods to cooperatively schedule their execution sequences. “ [5] This design pattern may also be referred to as Thread-safe Passive Object.

Monitor Object Design Pattern Pitfalls Calling wait() in unstable state 

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Forget to release lock when an exception occurs Not making the method synchronized when needed

Monitor Object Design Pattern Another Example monitor account { int balance := 0 function withdraw(int amount) { if amount < 0 then error "Amount may not be negative" else if balance < amount then error "Insufficient funds" else balance := balance - amount }

}

function deposit(int amount) { if amount < 0 then error "Amount may not be negative" else balance := balance + amount }

Monitor Object Design Pattern Consequences 

Pro’s

• Simplification of concurrency control implementation • Simplify synchronization of methods invoked concurrently on an object • Synchronized methods can cooperatively schedule their order of execution

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Con’s

• Concurrency remains complicated • Tightly coupling between object functionality and synchronization mechanisms • Nested monitor lockout • New problems, deadlocks and starvation

Monitor Object Design Pattern Known Uses  

Java Objects ACE Gateway

Conclusion Active Object:  Separates method invocation from method execution. Monitor Object:  Synchronizes method execution to ensure only one method runs within an object at a time.

Thank You

Questions?