Ongoing Optimization

Contents[Show]

Now it's time to put the theory into practice. The job is quite easy. A small program should undergo an ongoing optimization.

The program

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
// ongoingOptimization.cpp

#include <iostream>
#include <thread>

int x= 0;
int y= 0;

void writing(){
  x= 2000;
  y= 11;
}

void reading(){ 
  std::cout << "y: " << y << " ";
  std::cout << "x: " << x << std::endl;
}

int main(){
  std::thread thread1(writing);
  std::thread thread2(reading);
  thread1.join();
  thread2.join();
}

 

The program is quite simple. It consists of two threads thread1 and thread2.thread1 writes the values x and y. thread 2 reads the values x and y in the opposite direction.  The execution of the program is not so thrilling either.

ongoingOptimization

But you see, even this simple program has different results. So I finally come to my key idea.

 

Rainer D 6 P2 540x540Modernes C++ Mentoring

Stay informed about my mentoring programs.

 

 

Subscribe via E-Mail.

In the process of the ongoing optimization of the program, I have two questions in my mind.

  1. Is the program well defined? Precisely, is there a data race?
  2. Which values for x and y are possible?

The first question is often very challenging to answer. So I will reason in the first step about the program and I will verify in the second step my reasoning with CppMem.  If I have answered the first question, the second answer can easily be derived. I will provide the possible values in a table.

schabloneEng

 

But still, one question isn't answered yet? What do I mean by ongoing optimization? I mean by ongoing optimization, that I try to improve the program by weakening the C++ memory model. So in my journey, I discuss the following stations.

  • Non-atomic variables
  • Locks
  • Atomics with sequential consistency
  • Atomics with acquire-release semantic
  • Atomics with relaxed semantic
  • Volatile variables

What's next?

Of course, this was a very short post. But this post should provide you only the context of my ongoing optimization. In case you are bored, reason about the small program and answer the two question.

  1. Is the program well defined?
  2. Which values for x and y are possible?

Still bored? Then reason about the weakening of the memory model in the program and about the consequences. In the next post, I will analyse the unsynchronized access with the help of CppMem. Stay tuned.

 

 

 

 

 

Thanks a lot to my Patreon Supporters: Matt Braun, Roman Postanciuc, Tobias Zindl, G Prvulovic, Reinhold Dröge, Abernitzke, Frank Grimm, Sakib, Broeserl, António Pina, Sergey Agafyin, Андрей Бурмистров, Jake, GS, Lawton Shoemake, Animus24, Jozo Leko, John Breland, Venkat Nandam, Jose Francisco, Douglas Tinkham, Kuchlong Kuchlong, Robert Blanch, Truels Wissneth, Kris Kafka, Mario Luoni, Friedrich Huber, lennonli, Pramod Tikare Muralidhara, Peter Ware, Daniel Hufschläger, Alessandro Pezzato, Bob Perry, Satish Vangipuram, Andi Ireland, Richard Ohnemus, Michael Dunsky, Leo Goodstadt, John Wiederhirn, Yacob Cohen-Arazi, Florian Tischler, Robin Furness, Michael Young, Holger Detering, Bernd Mühlhaus, Matthieu Bolt, Stephen Kelley, Kyle Dean, Tusar Palauri, Dmitry Farberov, Juan Dent, George Liao, Daniel Ceperley, Jon T Hess, Stephen Totten, Wolfgang Fütterer, Matthias Grün, Phillip Diekmann, Ben Atakora, and Ann Shatoff.

 

Thanks in particular to Jon Hess, Lakshman, Christian Wittenhorst, Sherhy Pyton, Dendi Suhubdy, Sudhakar Belagurusamy, Richard Sargeant, Rusty Fleming, John Nebel, Mipko, Alicja Kaminska, and Slavko Radman.

 

 

My special thanks to Embarcadero CBUIDER STUDIO FINAL ICONS 1024 Small

 

My special thanks to PVS-Studio PVC Logo

 

My special thanks to Tipi.build tipi.build logo

Seminars

I'm happy to give online seminars or face-to-face seminars worldwide. Please call me if you have any questions.

Bookable (Online)

German

Standard Seminars (English/German)

Here is a compilation of my standard seminars. These seminars are only meant to give you a first orientation.

  • C++ - The Core Language
  • C++ - The Standard Library
  • C++ - Compact
  • C++11 and C++14
  • Concurrency with Modern C++
  • Design Pattern and Architectural Pattern with C++
  • Embedded Programming with Modern C++
  • Generic Programming (Templates) with C++

New

  • Clean Code with Modern C++
  • C++20

Contact Me

Modernes C++,

RainerGrimmDunkelBlauSmall

 

Comments   

0 #1 http://s600.net 2016-10-02 01:39
I enjoy the efforts you have put in this, appreciate it for
all the great posts.
Quote
0 #2 datablog 2016-10-05 00:14
Hiya, I am really glad I've found this info. Nowadays bloggers publish only about
gossips and internet and this is actually frustrating.
A good web site with interesting content, that is what I need.
Thank you for keeping this web site, I will be visiting it.
Do you do newsletters? Cant find it.
Quote
0 #3 Paul 2016-10-25 19:26
You have remarked very interesting points! ps nice web site.
Quote
0 #4 Photos For instagram 2016-10-29 01:54
I don't commonly comment but I gotta admit appreciate it
for the post on this perfect one :D.
Quote
0 #5 http://Iprps.mx 2016-11-16 12:32
Really wonderful visual appeal on this internet
site, I'd rate it 10 10.
Quote
0 #6 datenschmutz weblog 2016-11-18 19:26
Hello I am so grateful I found your site, I really found you
by mistake, while I was looking on Aol for something else, Anyways I am here now and would just like to say
thank you for a incredible post and a all round exciting blog (I
also love the theme/design), I don't have time to go through it all at the moment but I have book-marked it
and also included your RSS feeds, so when I have time I will be back to read
much more, Please do keep up the superb
job.
Quote
0 #7 Weldon 2016-12-03 16:05
Appreciate it for this wonderful post, I am glad I found this web site on yahoo.
Quote

Mentoring

Stay Informed about my Mentoring

 

English Books

Course: Modern C++ Concurrency in Practice

Course: C++ Standard Library including C++14 & C++17

Course: Embedded Programming with Modern C++

Course: Generic Programming (Templates)

Course: C++ Fundamentals for Professionals

Interactive Course: The All-in-One Guide to C++20

Subscribe to the newsletter (+ pdf bundle)

All tags

Blog archive

Source Code

Visitors

Today 3081

Yesterday 5317

Week 3081

Month 147252

All 11628406

Currently are 249 guests and no members online

Kubik-Rubik Joomla! Extensions

Latest comments