Search icon CANCEL
Subscription
0
Cart icon
Cart
Close icon
You have no products in your basket yet
Save more on your purchases!
Savings automatically calculated. No voucher code required
Arrow left icon
All Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Newsletters
Free Learning
Arrow right icon
Mastering C++ Multithreading
Mastering C++ Multithreading

Mastering C++ Multithreading: Write robust, concurrent, and parallel applications

By Maya Posch
$48.99
Book Jul 2017 244 pages 1st Edition
eBook
$39.99 $27.98
Print
$48.99
Subscription
$15.99 Monthly
eBook
$39.99 $27.98
Print
$48.99
Subscription
$15.99 Monthly

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Black & white paperback book shipped to your address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
Buy Now
Table of content icon View table of contents Preview book icon Preview Book

Mastering C++ Multithreading

Chapter 1. Revisiting Multithreading

Chances are that if you're reading this book, you have already done some multithreaded programming in C++, or, possibly, other languages. This chapter is meant to recap the topic purely from a C++ point of view, going through a basic multithreaded application, while also covering the tools we'll be using throughout the book. At the end of this chapter, you will have all the knowledge and information needed to proceed with the further chapters.

Topics covered in this chapter include the following:

  • Basic multithreading in C++ using the native API
  • Writing basic makefiles and usage of GCC/MinGW
  • Compiling a program using make and executing it on the command-line

Getting started


During the course of this book, we'll be assuming the use of a GCC-based toolchain (GCC or MinGW on Windows). If you wish to use alternative toolchains (clang, MSVC, ICC, and so on), please consult the documentation provided with these for compatible commands.

To compile the examples provided in this book, makefiles will be used. For those unfamiliar with makefiles, they are a simple but powerful text-based format used with the make tool for automating build tasks including compiling source code and adjusting the build environment. First released in 1977, make remains among the most popular build automation tools today.

Familiarity with the command line (Bash or equivalent) is assumed, with MSYS2 (Bash on Windows) recommended for those using Windows.

The multithreaded application


In its most basic form, a multithreaded application consists of a singular process with two or more threads. These threads can be used in a variety of ways; for example, to allow the process to respond to events in an asynchronous manner by using one thread per incoming event or type of event, or to speed up the processing of data by splitting the work across multiple threads.

Examples of asynchronous responses to events include the processing of the graphical user interface (GUI) and network events on separate threads so that neither type of event has to wait on the other, or can block events from being responded to in time. Generally, a single thread performs a single task, such as the processing of GUI or network events, or the processing of data.

For this basic example, the application will start with a singular thread, which will then launch a number of threads, and wait for them to finish. Each of these new threads will perform its own task before finishing.

Let's start with the includes and global variables for our application:

#include <iostream>
#include <thread>
#include <mutex>
#include <vector>
#include <random>

using namespace std;

// --- Globals
mutex values_mtx;
mutex cout_mtx;
vector<int> values;

Both the I/O stream and vector headers should be familiar to anyone who has ever used C++: the former is here used for the standard output (cout), and the vector for storing a sequence of values.

The random header is new in c++11, and as the name suggests, it offers classes and methods for generating random sequences. We use it here to make our threads do something interesting.

Finally, the thread and mutex includes are the core of our multithreaded application; they provide the basic means for creating threads, and allow for thread-safe interactions between them.

Moving on, we create two mutexes: one for the global vector and one for cout, since the latter is not thread-safe.

Next we create the main function as follows:

int main() {
    values.push_back(42);

We push a fixed value onto the vector instance; this one will be used by the threads we create in a moment:

    thread tr1(threadFnc, 1);
    thread tr2(threadFnc, 2);
    thread tr3(threadFnc, 3);
    thread tr4(threadFnc, 4);

We create new threads, and provide them with the name of the method to use, passing along any parameters--in this case, just a single integer:

    tr1.join();
    tr2.join();
    tr3.join();
    tr4.join();

Next, we wait for each thread to finish before we continue by calling join() on each thread instance:

    cout << "Input: " << values[0] << ", Result 1: " << values[1] << ", Result 2: " << values[2] << ", Result 3: " << values[3] << ", Result 4: " << values[4] << "\n";


    return 1;
}

At this point, we expect that each thread has done whatever it's supposed to do, and added the result to the vector, which we then read out and show the user.

Of course, this shows almost nothing of what really happens in the application, mostly just the essential simplicity of using threads. Next, let's see what happens inside this method that we pass to each thread instance:

void threadFnc(int tid) {
    cout_mtx.lock();
    cout << "Starting thread " << tid << ".\n";
    cout_mtx.unlock();

In the preceding code, we can see that the integer parameter being passed to the thread method is a thread identifier. To indicate that the thread is starting, a message containing the thread identifier is output. Since we're using a non-thread-safe method for this, we use the cout_mtx mutex instance to do this safely, ensuring that just one thread can write to cout at any time:

    values_mtx.lock();
    int val = values[0];
    values_mtx.unlock();

When we obtain the initial value set in the vector, we copy it to a local variable so that we can immediately release the mutex for the vector to enable other threads to use the vector:

    int rval = randGen(0, 10);
    val += rval;

These last two lines contain the essence of what the threads created do: they take the initial value, and add a randomly generated value to it. The randGen() method takes two parameters, defining the range of the returned value:

    cout_mtx.lock();
    cout << "Thread " << tid << " adding " << rval << ". New value: " << val << ".\n";
    cout_mtx.unlock();

    values_mtx.lock();
    values.push_back(val);
    values_mtx.unlock();
}

Finally, we (safely) log a message informing the user of the result of this action before adding the new value to the vector. In both cases, we use the respective mutex to ensure that there can be no overlap when accessing the resource with any of the other threads.

Once the method reaches this point, the thread containing it will terminate, and the main thread will have one less thread to wait for to rejoin. The joining of a thread basically means that it stops existing, usually with a return value passed to the thread which created the thread. This can happen explicitly, with the main thread waiting for the child thread to finish, or in the background.

Lastly, we'll take a look at the randGen() method. Here we can see some multithreaded specific additions as well:

int randGen(const int& min, const int& max) {
    static thread_local mt19937 generator(hash<thread::id>()(this_thread::get_id()));
    uniform_int_distribution<int> distribution(min, max);
    return distribution(generator)
}

This preceding method takes a minimum and maximum value as explained earlier, which limits the range of the random numbers this method can return. At its core, it uses a mt19937-based generator, which employs a 32-bit Mersenne Twister algorithm with a state size of 19937 bits. This is a common and appropriate choice for most applications.

Of note here is the use of the thread_local keyword. What this means is that even though it is defined as a static variable, its scope will be limited to the thread using it. Every thread will thus create its own generator instance, which is important when using the random number API in the STL.

A hash of the internal thread identifier is used as a seed for the generator. This ensures that each thread gets a fairly unique seed for its generator instance, allowing for better random number sequences.

Finally, we create a new uniform_int_distribution instance using the provided minimum and maximum limits, and use it together with the generator instance to generate the random number which we return.

Makefile

In order to compile the code described earlier, one could use an IDE, or type the command on the command line. As mentioned in the beginning of this chapter, we'll be using makefiles for the examples in this book. The big advantages of this are that one does not have to repeatedly type in the same extensive command, and it is portable to any system which supports make.

Further advantages include being able to have previous generated artifacts removed automatically and to only compile those source files which have changed, along with a detailed control over build steps.

The makefile for this example is rather basic:

GCC := g++

OUTPUT := ch01_mt_example
SOURCES := $(wildcard *.cpp)
CCFLAGS := -std=c++11 -pthread

all: $(OUTPUT)

$(OUTPUT):
    $(GCC) -o $(OUTPUT) $(CCFLAGS) $(SOURCES)

clean:
    rm $(OUTPUT)

.PHONY: all

From the top down, we first define the compiler that we'll use (g++), set the name of the output binary (the .exe extension on Windows will be post-fixed automatically), followed by the gathering of the sources and any important compiler flags.

The wildcard feature allows one to collect the names of all files matching the string following it in one go without having to define the name of each source file in the folder individually.

For the compiler flags, we're only really interested in enabling the c++11 features, for which GCC still requires one to supply this compiler flag.

For the all method, we just tell make to run g++ with the supplied information. Next we define a simple clean method which just removes the produced binary, and finally, we tell make to not interpret any folder or file named all in the folder, but to use the internal method with the .PHONY section.

When we run this makefile, we see the following command-line output:

$ make
g++ -o ch01_mt_example -std=c++11 ch01_mt_example.cpp

Afterwards, we find an executable file called ch01_mt_example (with the .exe extension attached on Windows) in the same folder. Executing this binary will result in a command-line output akin to the following:

$ ./ch01_mt_example.exe

Starting thread 1.

Thread 1 adding 8. New value: 50.

Starting thread 2.

Thread 2 adding 2. New value: 44.

Starting thread 3.

Starting thread 4.

Thread 3 adding 0. New value: 42.

Thread 4 adding 8. New value: 50.

Input: 42, Result 1: 50, Result 2: 44, Result 3: 42, Result 4: 50

What one can see here already is the somewhat asynchronous nature of threads and their output. While threads 1 and 2 appear to run synchronously, starting and quitting seemingly in order, threads 3 and 4 clearly run asynchronously as both start simultaneously before logging their action. For this reason, and especially in longer-running threads, it's virtually impossible to say in which order the log output and results will be returned.

While we use a simple vector to collect the results of the threads, there is no saying whether Result 1 truly originates from the thread which we assigned ID 1 in the beginning. If we need this information, we need to extend the data we return by using an information structure with details on the processing thread or similar.

One could, for example, use struct like this:

struct result {
    int tid;
    int result;
};

The vector would then be changed to contain result instances rather than integer instances. One could pass the initial integer value directly to the thread as part of its parameters, or pass it via some other way.

Other applications


The example in this chapter is primarily useful for applications where data or tasks have to be handled in parallel. For the earlier mentioned use case of a GUI-based application with business logic and network-related features, the basic setup of a main application, which launches the required threads, would remain the same. However, instead of having each thread to be the same, each would be a completely different method.

For this type of application, the thread layout would look like this:

As the graphic shows, the main thread would launch the GUI, network, and business logic thread, with the latter communicating with the network thread to send and receive data. The business logic thread would also receive user input from the GUI thread, and send updates back to be displayed on the GUI.

Summary


In this chapter, we went over the basics of a multithreaded application in C++ using the native threading API. We looked at how to have multiple threads perform a task in parallel, and also explored how to properly use the random number API in the STL within a multithreaded application.

In the next chapter, we'll discuss how multithreading is implemented both in hardware and in operating systems. We'll see how this implementation differs per processor architecture and operating system, and how this affects our multithreaded application.

Left arrow icon Right arrow icon
Download code icon Download Code

Key benefits

  • Delve into the fundamentals of multithreading and concurrency and find out how to implement them
  • Explore atomic operations to optimize code performance
  • Apply concurrency to both distributed computing and GPGPU processing

Description

Multithreaded applications execute multiple threads in a single processor environment, allowing developers achieve concurrency. This book will teach you the finer points of multithreading and concurrency concepts and how to apply them efficiently in C++. Divided into three modules, we start with a brief introduction to the fundamentals of multithreading and concurrency concepts. We then take an in-depth look at how these concepts work at the hardware-level as well as how both operating systems and frameworks use these low-level functions. In the next module, you will learn about the native multithreading and concurrency support available in C++ since the 2011 revision, synchronization and communication between threads, debugging concurrent C++ applications, and the best programming practices in C++. In the final module, you will learn about atomic operations before moving on to apply concurrency to distributed and GPGPU-based processing. The comprehensive coverage of essential multithreading concepts means you will be able to efficiently apply multithreading concepts while coding in C++.

What you will learn

[*] Deep dive into the details of the how various operating systems currently implement multithreading [*] Choose the best multithreading APIs when designing a new application [*] Explore the use of mutexes, spin-locks, and other synchronization concepts and see how to safely pass data between threads [*] Understand the level of API support provided by various C++ toolchains [*] Resolve common issues in multithreaded code and recognize common pitfalls using tools such as Memcheck, CacheGrind, DRD, Helgrind, and more [*] Discover the nature of atomic operations and understand how they can be useful in optimizing code [*] Implement a multithreaded application in a distributed computing environment [*] Design a C++-based GPGPU application that employs multithreading
Estimated delivery fee Deliver to United States

Economy delivery 10 - 13 business days

Free $6.95

Premium delivery 6 - 9 business days

$21.95
(Includes tracking information)

Product Details

Country selected

Publication date : Jul 28, 2017
Length 244 pages
Edition : 1st Edition
Language : English
ISBN-13 : 9781787121706
Category :
Concepts :

What do you get with Print?

Product feature icon Instant access to your digital eBook copy whilst your Print order is Shipped
Product feature icon Black & white paperback book shipped to your address
Product feature icon Download this book in EPUB and PDF formats
Product feature icon Access this title in our online reader with advanced features
Product feature icon DRM FREE - Read whenever, wherever and however you want
Buy Now
Estimated delivery fee Deliver to United States

Economy delivery 10 - 13 business days

Free $6.95

Premium delivery 6 - 9 business days

$21.95
(Includes tracking information)

Product Details


Publication date : Jul 28, 2017
Length 244 pages
Edition : 1st Edition
Language : English
ISBN-13 : 9781787121706
Category :
Concepts :

Table of Contents

17 Chapters
Title Page Chevron down icon Chevron up icon
Credits Chevron down icon Chevron up icon
About the Author Chevron down icon Chevron up icon
About the Reviewer Chevron down icon Chevron up icon
www.PacktPub.com Chevron down icon Chevron up icon
Customer Feedback Chevron down icon Chevron up icon
Preface Chevron down icon Chevron up icon
1. Revisiting Multithreading Chevron down icon Chevron up icon
2. Multithreading Implementation on the Processor and OS Chevron down icon Chevron up icon
3. C++ Multithreading APIs Chevron down icon Chevron up icon
4. Thread Synchronization and Communication Chevron down icon Chevron up icon
5. Native C++ Threads and Primitives Chevron down icon Chevron up icon
6. Debugging Multithreaded Code Chevron down icon Chevron up icon
7. Best Practices Chevron down icon Chevron up icon
8. Atomic Operations - Working with the Hardware Chevron down icon Chevron up icon
9. Multithreading with Distributed Computing Chevron down icon Chevron up icon
10. Multithreading with GPGPU Chevron down icon Chevron up icon

Customer reviews

Top Reviews
Rating distribution
Empty star icon Empty star icon Empty star icon Empty star icon Empty star icon 0
(0 Ratings)
5 star 0%
4 star 0%
3 star 0%
2 star 0%
1 star 0%
Top Reviews
No reviews found
Get free access to Packt library with over 7500+ books and video courses for 7 days!
Start Free Trial

FAQs

What is the delivery time and cost of print book? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela
What is custom duty/charge? Chevron down icon Chevron up icon

Customs duty are charges levied on goods when they cross international borders. It is a tax that is imposed on imported goods. These duties are charged by special authorities and bodies created by local governments and are meant to protect local industries, economies, and businesses.

Do I have to pay customs charges for the print book order? Chevron down icon Chevron up icon

The orders shipped to the countries that are listed under EU27 will not bear custom charges. They are paid by Packt as part of the order.

List of EU27 countries: www.gov.uk/eu-eea:

A custom duty or localized taxes may be applicable on the shipment and would be charged by the recipient country outside of the EU27 which should be paid by the customer and these duties are not included in the shipping charges been charged on the order.

How do I know my custom duty charges? Chevron down icon Chevron up icon

The amount of duty payable varies greatly depending on the imported goods, the country of origin and several other factors like the total invoice amount or dimensions like weight, and other such criteria applicable in your country.

For example:

  • If you live in Mexico, and the declared value of your ordered items is over $ 50, for you to receive a package, you will have to pay additional import tax of 19% which will be $ 9.50 to the courier service.
  • Whereas if you live in Turkey, and the declared value of your ordered items is over € 22, for you to receive a package, you will have to pay additional import tax of 18% which will be € 3.96 to the courier service.
How can I cancel my order? Chevron down icon Chevron up icon

Cancellation Policy for Published Printed Books:

You can cancel any order within 1 hour of placing the order. Simply contact customercare@packt.com with your order details or payment transaction id. If your order has already started the shipment process, we will do our best to stop it. However, if it is already on the way to you then when you receive it, you can contact us at customercare@packt.com using the returns and refund process.

Please understand that Packt Publishing cannot provide refunds or cancel any order except for the cases described in our Return Policy (i.e. Packt Publishing agrees to replace your printed book because it arrives damaged or material defect in book), Packt Publishing will not accept returns.

What is your returns and refunds policy? Chevron down icon Chevron up icon

Return Policy:

We want you to be happy with your purchase from Packtpub.com. We will not hassle you with returning print books to us. If the print book you receive from us is incorrect, damaged, doesn't work or is unacceptably late, please contact Customer Relations Team on customercare@packt.com with the order number and issue details as explained below:

  1. If you ordered (eBook, Video or Print Book) incorrectly or accidentally, please contact Customer Relations Team on customercare@packt.com within one hour of placing the order and we will replace/refund you the item cost.
  2. Sadly, if your eBook or Video file is faulty or a fault occurs during the eBook or Video being made available to you, i.e. during download then you should contact Customer Relations Team within 14 days of purchase on customercare@packt.com who will be able to resolve this issue for you.
  3. You will have a choice of replacement or refund of the problem items.(damaged, defective or incorrect)
  4. Once Customer Care Team confirms that you will be refunded, you should receive the refund within 10 to 12 working days.
  5. If you are only requesting a refund of one book from a multiple order, then we will refund you the appropriate single item.
  6. Where the items were shipped under a free shipping offer, there will be no shipping costs to refund.

On the off chance your printed book arrives damaged, with book material defect, contact our Customer Relation Team on customercare@packt.com within 14 days of receipt of the book with appropriate evidence of damage and we will work with you to secure a replacement copy, if necessary. Please note that each printed book you order from us is individually made by Packt's professional book-printing partner which is on a print-on-demand basis.

What tax is charged? Chevron down icon Chevron up icon

Currently, no tax is charged on the purchase of any print book (subject to change based on the laws and regulations). A localized VAT fee is charged only to our European and UK customers on eBooks, Video and subscriptions that they buy. GST is charged to Indian customers for eBooks and video purchases.

What payment methods can I use? Chevron down icon Chevron up icon

You can pay with the following card types:

  1. Visa Debit
  2. Visa Credit
  3. MasterCard
  4. PayPal
What is the delivery time and cost of print books? Chevron down icon Chevron up icon

Shipping Details

USA:

'

Economy: Delivery to most addresses in the US within 10-15 business days

Premium: Trackable Delivery to most addresses in the US within 3-8 business days

UK:

Economy: Delivery to most addresses in the U.K. within 7-9 business days.
Shipments are not trackable

Premium: Trackable delivery to most addresses in the U.K. within 3-4 business days!
Add one extra business day for deliveries to Northern Ireland and Scottish Highlands and islands

EU:

Premium: Trackable delivery to most EU destinations within 4-9 business days.

Australia:

Economy: Can deliver to P. O. Boxes and private residences.
Trackable service with delivery to addresses in Australia only.
Delivery time ranges from 7-9 business days for VIC and 8-10 business days for Interstate metro
Delivery time is up to 15 business days for remote areas of WA, NT & QLD.

Premium: Delivery to addresses in Australia only
Trackable delivery to most P. O. Boxes and private residences in Australia within 4-5 days based on the distance to a destination following dispatch.

India:

Premium: Delivery to most Indian addresses within 5-6 business days

Rest of the World:

Premium: Countries in the American continent: Trackable delivery to most countries within 4-7 business days

Asia:

Premium: Delivery to most Asian addresses within 5-9 business days

Disclaimer:
All orders received before 5 PM U.K time would start printing from the next business day. So the estimated delivery times start from the next day as well. Orders received after 5 PM U.K time (in our internal systems) on a business day or anytime on the weekend will begin printing the second to next business day. For example, an order placed at 11 AM today will begin printing tomorrow, whereas an order placed at 9 PM tonight will begin printing the day after tomorrow.


Unfortunately, due to several restrictions, we are unable to ship to the following countries:

  1. Afghanistan
  2. American Samoa
  3. Belarus
  4. Brunei Darussalam
  5. Central African Republic
  6. The Democratic Republic of Congo
  7. Eritrea
  8. Guinea-bissau
  9. Iran
  10. Lebanon
  11. Libiya Arab Jamahriya
  12. Somalia
  13. Sudan
  14. Russian Federation
  15. Syrian Arab Republic
  16. Ukraine
  17. Venezuela