In this article we will look at pthreads creation, management and applications in linux operating system using practical examples, code snippets.

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Multithreading example program

#include <stdio.h>
#include <pthread.h>

#define LOOPS 1000
int result = 0;

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; 

void *AddFunc(void *a) {
  int aoffset = *(int *) a;
  for(int i = 0; i < LOOPS; i++) {
    //Start critical section
    pthread_mutex_lock(&mutex);
    result += aoffset;
    //End critical section
    pthread_mutex_unlock(&mutex);
  }
  pthread_exit(NULL);
}

void *SubtractFunc(void *s) {
  int soffset = *(int *) s;
  for(int j = 0; j < LOOPS; j++) {
    //Start critical section
    pthread_mutex_lock(&mutex);
    result += soffset;
    //End critical section
    pthread_mutex_unlock(&mutex);
  }
  pthread_exit(NULL);
}

int main(void) {
  pthread_t thread_id1;
  pthread_t thread_id2;

  int offset1 = 1, offset2 = -1;
  
  pthread_create(&thread_id1, NULL, AddFunc, &offset1);
  pthread_create(&thread_id2, NULL, SubtractFunc, &offset2);

  //Wait for threads to finish
  pthread_join(thread_id1, NULL);
  pthread_join(thread_id2, NULL);

  printf("The result is:%d\n", result);

  return 0;
}

Let's compile the Listing1.c program as shown in the following program output.

pi@raspberrypi:~/try $ gcc prog.c -lpthread
pi@raspberrypi:~/try $ ./a.out
The result is:0
pi@raspberrypi:~/try $

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