Skip to main content

Multithreading Example using POSIX Threads

Requirements : GCC Compiler and any Linux OS with pthread Library


There are two threads in the following program which are implemented using function pointers, in which one thread is helpful for getting a input from the keyboard and other thread is helpful to convert it to upper case letters. But here both the threads does not depends on each other.

 That is, the second thread automatically converts the string to upper case letters itself, does not bothering about the first thread(the string entered through the keyboard). Two seconds delay is given to enter the string via the key board.



#include <stdio.h>

#include <unistd.h>

#include <stdlib.h>

#include <string.h>

#include <ctype.h>

#include <pthread.h>

#define BUFFER_SIZE 1024

char buffer[BUFFER_SIZE];

void *read_thread(void *arg)


while(strncmp("stop", buffer,4) !=0)


printf("enter text:");

fgets(buffer,BUFFER_SIZE, stdin);



pthread_exit("Read thread exit successful");


void *convert_thread()


int i;




printf("Converted text:");




pthread_exit("Convert_thread exit successful");


int main()


int result;

pthread_t rthread, cthread;

void *thread_result;

printf("enter text, the program will convert it into upper case, to stop enter 'stop'\n");

result=pthread_create(&rthread, NULL, read_thread, NULL);

if(result != 0)


printf("Read_thread creation failed");



result=pthread_create(&cthread, NULL, convert_thread, NULL);

if(result != 0)


printf("Cpnvert_thread creation failed");



result=pthread_join(rthread, &thread_result);

if(result != 0)


printf("read_thread join failed");



printf("read_thread joined, %s\n", thread_result);

result=pthread_join(cthread, &thread_result);

if(result !=0)


printf("convert_thread join failed");



printf("convert_thread joined, %s\n", thread_result);


return 0;



In this program, one thread reads the input and another thread converts the input string into upper case letters. This is repeated till 'stop' typed.

The prorgam can be compiled by

$ gcc -o multithread multithread.c -lpthread

After observing the output the lack of coordination between the two threads is evident. Even if the input is not given from the keyboard, the thread does the conversion to upper case letter. So to avoid that, it is necessary to use semaphores.


Popular posts from this blog

Implementing a new system call in Kernel version 2.6.32

A system call is used by application or user programs to request service from the operating systems. Since the user programs does not have direct access to the kernel whereas the OS has the direct access. OS can access the hardware through system calls only. The following files has to be modified for implementing a system call /usr/src/linux- /usr/src/linux- /usr/src/linux- /usr/src/linux- New set of files to be created Create a new directory newcall/ inside the path “ /usr/src/linux- ” Create new files Makefile, newcall.c and put them in the /usr/src/linux- folder Create new user files (in any folder of Linux) to test the system call testnewcall.c, testnewcall.h (created in /home/pradeepkumar ) syscall_table_32.S Find the file /usr/src/linux-

How to Access MOODLE in Intranet and Internet

When Moodle is accessed either in Intranet or internet, there will not be any issue. But occasions when the MOODLE Site has to be accessed both in the intranet and in the Internet, here is a simple trick Server Used: IBM Blade Servers Operating system: Windows Server 2008 Moodle Version: 2.4 WAMP Server is used. Number of Users: 3000 (Students) + 200 (Faculty) Open the config.php from ~/moodle/config.php include these lines $CFG->wwwroot = 'http://'.$server_id.'/vitcc'; $CFG->dataroot  = 'C:\\wamp\\moodledata'; before the following line $CFG->directorypermissions = 07xx; Restart the WAMP Server and you can Check MOODLE Site both in Internet and Intranet. The above Image tells the intranet Link and the internet link can be opened outside the campus network

Electrical Machine Design (equations)

Factors DC Machine Transformers Induction Machines Synchronous Machines Output Equation P a =C o D 2 Ln, where Pa=P/h for generators, Pa=P for motors For Single Phase Q=2.22 f B m A i K w A w d 10 -3 For Three Phase Q=3.33 f B m A i K w A w d 10 -3 Q=C o D 2 L n s KVA Input Q= HP * 0.746 / Cos f * h Q=C o D 2 L n s KVA Input Q= HP * 0.746 / Cos f * h For Turbo alternators Q=1.11B av ac K ws V a 2 L 10 -3 /n s Output Coefficient C o =B av ac* 10 -3 where Bav-magnetic loading and ac - electric loading DNA C o =11 K ws B av ac 10 -3 C o =11 K ws B av ac 10 -3 Choice of Magnetic Loading Flux Density in Teeth Frequency of Flux Reversals Size of machine DNA Magnetizing current, Flux Density, Iron loss Iron loss, Stability, Voltage Rating, Parallel Operation, Transient ShortCircuit current