Homepage of Ingo Klöckl
 Home
 Programmieren
 - Toolbox
 - Java
 - PostScript
 - Perl
 - Assembler
 - Links
 - Download
Ingo Klöckl
i.kloeckl@2k-software.de

Programming POSIX threads on Linux

Part I: Thread basics

On this page, I want to give a very short overview over the programming of POSIX threads on a Linux box. At the moment, my perspective lays on a working example, not a complete tutorial (for such, please have a look at the references), and the prerequisites necessary for compiling and linking the example on Linux. So if you know a bit what's going on with the pthread library and just look for the right compiler switch, or you have already programmed threads, but forgotten which parameter is the thread attribute struct, your are right here :-)

The source code

Now first let's have a look to the source code of a real program, thread.c. It does not do neither much nor exciting things, just sleeps for a random time interval. The special is, that the sleeping is done in a separate thread, and the number of threads can be controlled by the command line. The source code is written in C and can be downloaded here.

Compiling and linking

For your commodity, you can compile and link the program with the following Makefile, which is not the smallest possible version (in fact, I cloned it from another project, feel free to minimize it by yourself). With this Makefile in your working directory, you can simply type make to create or re-create the executable thread.

Usage

The program is started by a command line: 

thread 5
This call lets the program create 5 threads which will wait a random time interval. The main line of the program will wait for each thread, in the same order the threads are created. This is necessary, because only after joining the thread to the main line via pthread_join, you can catch the thread's return value. Unfortunately, it is only possible to wait for termination of a specified thread, not for one of a set of threads, so we will wait for the longest-running thread to complete, even if all other are already finished. This may be a problem in some applications, so please have a look at part II of this article, where a condition variable is used to overcome this limitation of pthread_join.

Programmer's quick reference

Each program using POSIX threads has to include the following header file: 

#include <pthread.h>
To succesfully compile and link the program, you have to speficy the following compiler switches and libraries, which are included in the Makefile: 
-D_REENTRANT	% compiler switch
-lpthreads	% linker lib

Here are the most important POSIX functions concerning the basics of thread programming. For a quick reference, they are given as function prototypes. The usage is shown in the example source code. 

int pthread_create(pthread_t* tid, const pthread_attr_t* attr,
  void* (*func)(void* arg), void* arg);

  return value: 0 if OK, positive error code otherwise


int pthread_join(pthread_t tid, void** status);

  return value: 0 if OK, positive error code otherwise


pthread_t pthread_self(void);

  return value: thread ID of the calling thread


int pthread_detach(pthread_t tid);

  return value: 0 if OK, positive error code otherwise


void pthread_exit(void* status);

  no return to caller :-)

References

Literature

  • R. W. Stevens, Unix Network Programming, vol. II: Interprocess Communications, Prentice-Hall. A very good book in two volumes which can be seen as classic text about every aspect of Unix network programming, including sockets, threads, IPC and RPC.

Online ressourcen

There are quite a lot of good web sites offering detailed information about POSIX threads. A very incomplete selection follows: