darwin applied to labview: the evolution of the data management

www.mesulog.fr

Darwin applied to LabVIEW :

The evolution of the data management

Luc DESRUELLE – Certified LabVIEW Architect

The survival of the fittest applied to the LabVIEW Dataflow model

Summary

I. MESULOG & the conference speaker

II. Overview: Dataflow model & Data communication

III. Darwin & LabVIEW

IV. Darwin & Data communication methods

V. To OOP

VI. To Framework

Luc DESRUELLE - Darwin applied to LabVIEW : The evolution of the data 2

MESULOG

www.mesulog.fr

Activity: Test and measurement Software development

Skills: LabVIEW (Windows, RT, FPGA, PDA, DSC),

TestStand

VeriStand

Location: Grenoble (France)

National Instruments Alliance Member

LabVIEW and TestStand Certified


http://www.mesulogfr/

Luc DESRUELLE

Software Architect

NI Forums Community

CLA

The conference speaker


Community blog

• Blank diagram syndrome

• Development rules

• Animated gif to avoid code

• Transparent Windows

• LabVIEW Project

• OOP

• Modbus

• ….

https://decibel.ni.com/content/blogs/Luc_Desruelle

Author of the LabVIEW French book « LabVIEW : programming and applications »

3rd Edition, Dunod 05/2015, Prefaced by Jeff Kodosky

book website link

Chapter 1: LabVIEW EDI and dataflow programming environment

Chapter 2: Data communication methods

Chapter 3: Advanced knowledge and skills to design, develop and deploy a

scalable, readable and maintainable application .

Chapters 4, 5 and 6: Data acquisition, analysis and report.

The conference speaker


https://www.dunod.com/sciences-techniques/sciences-techniques-industrielles/automatique-robotique/ouvrages-professionnels/labview



II] Overview


LabVIEW Dataflow model

LabVIEW follows a dataflow model

Dataflow programming does not usually require variables.

For a literal implementation of this model.

Dataflow models describe nodes as:

consuming data inputs

producing data outputs.

Advanced concepts : LabVIEW contains many data communication methods.

For example, local and global variables are not inherently part of the LabVIEW

dataflow execution model.

Darwin applied to LabVIEW : The evolution of the data 7

Source: Data Communication Methods in LabVIEW

http://zone.ni.com/reference/en-XX/help/371361L-01/lvconcepts/data_comm/

"Always" the same observation

LabVIEW Rookie mistakes:1 time OK

But Exaggeration prevents the evolution


LabVIEW

Spaghetti

The most famous LabVIEW code

Data Communication Methods

LabVIEW contains many “data communication” methods, each suited for a

certain use case.

Can by order into 3 types:

Dataflow elements, the primary methods

Variable Interfaces

Buffer Interfaces


Source: Data Communication Methods in LabVIEW

Dataflow Elements

• Wire

• Shift register

• Feedback Node

Variable Interfaces

• Local variable

• Global variable

• FGV

• AE

• DVR

• …

Buffer Interfaces

• Queue

• User events

• RT FIFO

• …

Data Communication methods

http://zone.ni.com/reference/en-XX/help/371361L-01/lvconcepts/data_comm/

The presentation

Evolution of Data communication methods,

Dataflow element to Variable Interfaces, to Buffer Interfaces

To store a value in memory

To access the value

This presentation does answer the following questions:

why avoiding local, global, Property Node?

Which method to use? Why?

For diner tonight: local, global, FGV, AE, DVR, OOP, State Machine and QMH.

Speed demonstration, UI thread, memory management (buffer copies) and Race

Conditions with simples and downloadable examples.


III] Darwin & LabVIEW


Darwin

Charles Robert Darwin (1809 – 1882)

All species of life have descended from one common

ancestor

This branching pattern of evolution resulted from the

natural selection

The survival of the fittest


With deep humor this presentation makes the link

between

the evolution of the LabVIEW data management

and the Darwin's Theory of Evolution

the survival of the fittest

Darwin & LabVIEW


Darwin LabVIEW

One common ancestor LabVIEW Control

All species of life All data communication methods

The survival of the fittest The survival of the most scalable

II] Data communication

Once upon a time…. A very nice Data…


Dataflow elements

Data transfer

To take advantage of the dataflow

The primary data communication methods in your

application


Dataflow Elements

Dataflow Elements

•Wire = between objects

• Shift register = between loop iterations

• Feedback Node = between iterations

Variables Interfaces

Store a value in memory

Value that Readers and writers can access

Advanced concepts


Dataflow Elements

Variable Interfaces

• Local variable

•Global variable

•…

•…

Variables interfaces

others…

Quiz N°1

CLAD exam: Which of the following is the best method

to update an indicator on the front panel?

A. Use a Local variable

B. Wire directly to the indicator « Data Out »

C. Use an implicit « value » property node

D. Use an explicit « value » property node (reference)


Quiz N°1 Demo: Execution speed

Demo


For 10 000 iterations Time (ms)

Indicator 100

Local 100

Global 100

Property node (implicit) 4 000

Property node (explicit) 4 000

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Indicator Local Global Property

node

(implicit)

Property

node

(explicit)

Quiz N°1: Explanation

Synchronous nodes

A few nodes are synchronous, meaning they do not multitask

with other nodes.

In a multithreaded application, they run to completion, and the

thread in which they run is monopolized by that task until the

task completes.

Property Nodes

Synchronize with the UI thread, even for the Value property

Cause the front panel of a subVI to remain in memory

Force a front-panel redraw every time you update the value


Source: Multitasking in LabVIEW

http://zone.ni.com/reference/en-XX/help/371361J-01/lvconcepts/multitasking_in_labview/

Quiz N°1 Front panel in memory

When front panel is in memory: which can cause

unnecessary memory usage -> Buffer copies

Programmation Avancée sous LabVIEW 20

Buffer copy

Operate Buffer

Transfer Buffer

Execution Buffer

Buffer copy

Quiz N°1 Explanation

Memory consideration

Local variables make copies of the data buffers

Global variables make copies of the data buffers

Have slower execution speed than using a wire


Quiz N°1 Property node VS local

Property node Buffer copies

UI Thread

Front panel redraw

Synchronous node

Front-panel in memory

Race Condition


Local variable

Buffer copies

Any Threads

Race condition

V.S.

Quiz N°1: Answer

1. Indicator

2. Local variable

3. Implicit property node

4. Explicit property node


Quiz N°2

To store the variable "Data In", what is best? Wiring

“Data In” to:

A. Local variable « Data Out »

B. Global variable « Data »


Quiz N°2 Answer


Local variable VS Global variable

The game is a draw

Overview

Avoid local variables – global variables - property nodes

Buffers Copies

Slower execution

Race Conditions

No error handler

1 time OK but Exaggeration prevents the evolution


How to avoid local variables, global variables and

property nodes

How ????

To avoid


FGV : Functional Global Variable or LV2

Provide global access to data

VI that uses uninitialized shift register (USR)

Non reentrancy is required

To store a data: Set (Writers)

To share the « global » data: Get (Readers)

FGV: Functional Global Variable


Writer Reader

Quiz N°3

Why the names :

FGV or LV2 Style Global or VIGlobals or….?


Quiz N°3 Answer : HIStory

Same as: HIStory World Tour (Michael Jackson 1997)

LabVIEW HIStory Version Tour: FGV or LV2 Style

Global or VIGlobals?

Prior to LabVIEW 2: the value of the initialized shift register

had not been defined.

LabVIEW 2: uninitialized shift register would retain its

previous value.

This technique became the methodology for storing global

data in LabVIEW.

The native global variable was not introduced until

LabVIEW 3.

FGV is a Global… VIGlobal

Source: Advanced Architectures in LabVIEW


FGV: Example


2 cases:

> Set = Store

> Get = share

Store data

Race conditions

Race conditions ?????????????


Race conditions

Race conditions: The evolution of the fittest


Race condition: a bug

Race condition or race hazard: output is dependent on

the sequence of other uncontrollable events.

The term originates with the idea of two signals racing

each other to influence the output first.

Unpredictable outcomes = A bug!!!!


Data Out = ??

X=1 or 0

Y=1 or 0(0;0) or (0;1)

or (1;0) or(1;1)

X=0 et

Y=0

Source : https://en.wikipedia.org/wiki/Race_condition

Quiz N°4

Does FGV prevents the Race Conditions?


Data Out = ??

X = ?

Y= ?

Data In

X = 0

Y= 0

Quiz N°4: Result

No (with multi-writers)

LabVIEW code demo

Download code MESULOG website >> Société >> Présentations Techniques

www.mesulog.fr/presentations_techniques


http://www.mesulog.fr/presentations_techniques

FGV: recommended Use

Only 1 writer

N Readers


To share a « global » data: only 1 writer

Race conditions & N Writers

N Writers (not only 1 writer)

How to Avoid Race conditions ?????????????

N Writers

N Readers


AE : Action Engine : FGV evolution with actions

Not only set and get methods

Actions = Encapsulate data and code = block other instance

until complete execution

Actions that modify data = critical section

Data protection: private access, data is always private

AE : Action Engine


AE : Action Engine


EncapsulationAction that modify the dataData is always private

AE: Example

Example

FGV + Actions (enum)

Reusable modules – simplified LV code – Error Handler –

more readable


LV Code that

modify the

data

ActionsStore Data

(private)

Quiz N°5

Does AE prevents Race Conditions?


Data Out = ??

X = ?

Y= ?Data In

X = 0

Y= 0

Quiz N°5: Answer

YES

Encapsulation: LV Code that modify the data, data is

always private = prevents Race Conditions

LabVIEW code demo





Reference

Reference

Reference

DVR: Data Value Reference

Reference is a pointer to the data

Wire is the reference, not the data


Data Copy

Data Copy

Data

Avoid Race Conditions

Quiz N°5

Which of the following statements regarding the DVR

are true:

A. Forking creates a copy of the reference, not a copy of the

data

B. Avoid data copies

C. Avoid Race conditions

D. Allow error handler


Quiz N°5: Answer

A, B, C & D are all true

LabVIEW code demo





Overview: variable interfaces


Variable Interfaces

1 time OK but Exaggeration prevents the evolution

The evolution of the fittest• N Writers• Reusable modules• Error Handler• Avoid data copies• Avoid Race Conditions

Overview: variable interfaces


Features - Scalable

Simplicity

to Buffer Interfaces

To avoid overwriting or losing any value

Buffer Interfaces, for example: Queue


Enqueue Element

Obtain Queue

Dequeue Element

Release Queue1 2 4

3

1 2 3 4

to go further with the… evolution


Data communication

Dataflow Elements

Wire

Shift register

Feedback Node

Variable Interfaces

Inter-Target

Local & Global

FGV -> AE

DVR

Networked Shared variable

Buffer Interfaces

Intra-TargetQueue

User events

NetworkedTCP

Network Streams

Data communication methods in LabVIEW (without RT and FPGA)

V] OOP


From variable interfaces to OOP

Variable Interfaces

OOP

OOP

A class is a collection of data (attributes) and methods that allow to

change these data

Attributes are private

Encapsulation

Inheritance

Dynamic dispatch


Class

Attributes

methodsCode

LabVIEW and OOP

OOP is a evolution from the AE (according to Darwin)

Shift Register become “attributes”

Actions become “methods”

Native LabVIEW class = by value


Action n°1

= case 1

Action n°2

= case 2

Action …

= case

1. Data = shift register

2. Actions = states

Actions = methods

1 method = 1 vi

AE = Action Engine

OOP

More advanced concepts:

Inheritance

Dispatch dynamic

Quiz N°6

Does OOP by Value prevents Race Conditions?


Data Out = ??

X = ?

Y= ?

Data In

X = 0

Y= 0

Quiz N°6: answer

OOP by Value? No

Forking creates a copy of the data

LabVIEW code demo





To OOP by Ref


OOP by Ref

Quizz N°7

OOP by Ref prevents the Race Conditions?


Résultat Quizz N°7

Yes

Forking creates a copy of the reference, not a copy of the data

Démonstration code LabVIEW

Code téléchargeable sur le site MESULOG >> Société >> Présentations Techniques




VI] Framework


Evolution to framework…

Framework

Variable Interfaces

Action Engine (AE): execute only one action then

stops

Need to add transitions to perform multiple actions

Need to describe a “Moore Machine”?

More “scalable” ?

The evolution of the Action to the state


Moore Machine or State Machine


InitCheck

statusCleanup

Measure

5000 ms

125ms

Quit buttondefault

Transitionswhich state to go to next

Moore Machine

Idle Cleanup

Quit button

« state & transition »

States = performs a specific action for each state in the

diagram

Transition = in-state calculation to determine which state to go

to next

A terminal state is the final state executed and performs

cleanup actions.

Any algorithm described by a “Moore machine”

State Machine


InitCheck

statusCleanup

Measure

5000 ms

125ms

Quit bouton

default

Source : white-paper State Machine

http://www.ni.com/white-paper/3024/en/

State Machine: grey's anatomy


Shift register to store the

value of the current state

The case structure contains one frame

for each state (Moore Machine)

Shift register to store

private data

Next state : contains state transition

information, which state to go to next

Typdef EnumFirst State Next State

State

?

Code

While Loop

State Machine: LabVIEW Example

Demo


InitCheck

statusCleanup

Measure

5000 ms

Quit bouton

default

Demo

State Machine: LabVIEW Example


One frame for each

State

Loop Timing

Shift register

State Machine: Overview

One of the fundamental LabVIEW architectures

(basic!)

Use to build applications quickly (Moore Machine)

Source CLAD exam: What is one disadvantage of

using the State Machine VI architecture?

If two state changes occur at the same time, only the first

state change will be handled and the second will be lost

Why?

Shift register is used to store the value of the next state

Shift register store only the current value


State Machine: evolution?

It is important to avoid losing any value…

No shift register

No variable interfaces

Evolution???

You must use:

Buffer interfaces

FIFO queue for example


Evolution? Queue State machine


Queue State Machine

FIFO Queue

Other? Event Structure

For handling user interactions

Dialog box for example

Waits until an event happens, then executes the appropriate

case to handle that event.

Optional Timeout (wait for an event to occur)


Event structure example


Other? Producer/Consumer

For data sharing between multiple process

Two process categories:

those that produce data,

those that consume the data produced.

Data buffering:

Data queues (Message)

Communicate data between loops


QMH


QMH: Queue Message Handler

QMH: a combination of all

QMH: Queue Message Handler

Is a combination of (evolution of!)

producer/consumer

event handler

state machine

Overview

multiple sections of code (task)

running in parallel

sending data (Message) between them (Queue)

Error handling

Project organization


= State (required)

= Data (optional)

QDMH

Grey's anatomy

1. The producer loop (EHL) contains an event structure that sends

messages to the consumer loop.

2. The consumer (MHL) receives and processes the messages in

a state machine.

3. A message can be triggered by UI events or from other states

in the state machine

Provides a powerful and efficient architecture


Source : white-paper QMH

http://www.ni.com/tutorial/14119/fr/

State Machine: grey's anatomy

demo


2_Send a message

1_Obtain Queue3_ receives the

messages 5_can add a

message

4_ executes the

appropriate

case

Shift register to store

private data


The End: Exaggeration prevents the evolution

Framework

Variable interfaces

OOP

Dataflow Elements

Buffer Interfaces

Inter-Target

Inter-Target

Networked

Networked

The survival of the most scalable

More speaker Links

More technical presentationswww.mesulog.fr/presentations_techniques

National Instruments : luc desruelle's Blogue

Tutorials developpez.com : luc Desruelle

tools that wish you well (Best practices for managing large LabVIEW applications)

More French book"LabVIEW programmation et applications" 3iéme édition, Dunod

More National Instruments Francophone websitesForum francophone NI LabVIEW

Forum francophone Autres produits NI

Communauté Francophone

Luc Desruelle | LinkedIn



https://decibel.ni.com/content/blogs/Luc_Desruelle

http://luc-desruelle.developpez.com/tutoriels/labview/extrait-livre-programmation-application/

http://www.mesulog.fr/download/nidays2014_MESULOG_LesOutilsQuiVousVeulentDuBien.pdf


http://forums.ni.com/t5/Discussions-au-sujet-de-NI/bd-p/4171

http://forums.ni.com/t5/Discussions-au-sujet-des-autres/bd-p/4170

https://decibel.ni.com/content/community/regional/france/labview

https://www.linkedin.com/in/labviewcertifiedeveloppeur

Where to find help?

Community is working for you

2 NI “Francophone” Forums http://forums.ni.com/t5/Discussions-au-sujet-de-NI/bd-p/4171


1 “Francophone” community https://decibel.ni.com/content/community/regional/france/labview

Rencontre développeurs : cf LUGE

And… All websites forums et communities, for example LabVIEW Development Best Practices

Large Applications : ni.com/largeapps

LAVA


http://forums.ni.com/t5/Discussions-au-sujet-de-NI/bd-p/4171


https://decibel.ni.com/content/community/regional/france/labview

https://decibel.ni.com/content/groups/large-labview-application-development

MESULOG: About us

www.mesulog.fr

Past projects

Technical Presentations

LabVIEW

TestStand

VeriStand


Past projects

Company -> Technical Presentations

http://www.mesulog.fr/

MESULOG: Our customers

Our customers:

ALSTOM Grid

AREVA NP

CEA (Commissariat à l'Énergie Atomique)

CETIAT (Centre Technique des Industries Aérauliques et Thermiques)

CNES (Centre National d'Études Spatiales)

CNRS (Centre National de la Recherche Scientifique)

EDF

HONEYWELL Security

LNE (Laboratoire National d'Essais)

ONERA

PECHINEY

RADIALL

RENAULT

STMicroelectronics

THALES Alenia Space

THALES LCD...


Questions


darwin applied to labview: the evolution of the data management

Documents