Book Image

Linux System Programming Techniques

By : Jack-Benny Persson
Book Image

Linux System Programming Techniques

By: Jack-Benny Persson

Overview of this book

Linux is the world's most popular open source operating system (OS). Linux System Programming Techniques will enable you to extend the Linux OS with your own system programs and communicate with other programs on the system. The book begins by exploring the Linux filesystem, its basic commands, built-in manual pages, the GNU compiler collection (GCC), and Linux system calls. You'll then discover how to handle errors in your programs and will learn to catch errors and print relevant information about them. The book takes you through multiple recipes on how to read and write files on the system, using both streams and file descriptors. As you advance, you'll delve into forking, creating zombie processes, and daemons, along with recipes on how to handle daemons using systemd. After this, you'll find out how to create shared libraries and start exploring different types of interprocess communication (IPC). In the later chapters, recipes on how to write programs using POSIX threads and how to debug your programs using the GNU debugger (GDB) and Valgrind will also be covered. By the end of this Linux book, you will be able to develop your own system programs for Linux, including daemons, tools, clients, and filters.
Table of Contents (14 chapters)

Reading return values from threads

In this recipe, we'll continue from the previous recipe. Here, we'll fetch the answers as return values from the threads instead of letting them print the result themselves. This is like the return values from functions.

Knowing how to fetch the return values from threads enables you to do much more complicated things with threads.

Getting ready

In order for this recipe to make sense, it's advised that you complete the previous recipe first.

You'll also need the Makefile that we wrote in the previous recipe.

How to do it…

This program is similar to that of the previous recipe, but instead of each thread printing its own result, they return it to main(). This is similar to how functions return a value to main(), only here we need to do some casting back and forth. The downside of this approach is that we won't see the result until both threads are finished unless we intentionally give the first thread...