Multi-Threaded programming with a critical section is a quite difficult problem. In the simplest form, these problems require semaphores to synchronize them. In this context, the following program illustrates how semaphore is used for multi-threading problems with critical sections.
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <semaphore.h>
#define SIZE 1024
void *my_thread_function(void *arg);
sem_t binary_semaphore_var;
char str[SIZE];
int main() {
int res;
pthread_t my_thread_a;
void *thread_result;
res = sem_init(&binary_semaphore_var, 0, 0);
if (res != 0) {
perror("Semaphore initialization failed");
exit(EXIT_FAILURE);
}
res = pthread_create(&my_thread_a, NULL, my_thread_function, NULL);
if (res != 0) {
perror("Thread creation failed");
exit(EXIT_FAILURE);
}
printf("Input some text or enter end to finish\n");
while (strncmp("end", str, 3) != 0) {
fgets(str, SIZE, stdin);
sem_post(&binary_semaphore_var);
}
printf("\nWaiting for thread to finish...\n");
res = pthread_join(my_thread_a, &thread_result);
if (res != 0) {
perror("Thread join failed");
exit(EXIT_FAILURE);
}
printf("Thread joined\n");
sem_destroy(&binary_semaphore_var);
exit(EXIT_SUCCESS);
}
void *my_thread_function(void *arg) {
sem_wait(&binary_semaphore_var);
while (strncmp("end", str, 3) != 0) {
printf("You input %d characters\n", strlen(str) -1);
sem_wait(&binary_semaphore_var);
}
pthread_exit(NULL);
}
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