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Print numbers in sequence using thread synchronization
Here we will see how to print numbers in a correct sequence using different threads. Here we will create n number of threads, then synchronize them. The idea is, the first thread will print 1, then second thread will print 2 and so on. When one thread is trying to print, it will lock the resource, so no thread can use that portion.
Example
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t* cond = NULL;
int threads;
volatile int count = 0;
void* sync_thread(void* num) { //this function is used to synchronize the threads
int thread_number = *(int*)num;
while (1) {
pthread_mutex_lock(&mutex); //lock the section
if (thread_number != count) { //if the thread number is not same as count, put all thread
except one into waiting state
pthread_cond_wait(&cond[thread_number], &mutex);
}
printf("%d ", thread_number + 1); //print the thread number
count = (count+1)%(threads);
// notify the next thread
pthread_cond_signal(&cond[count]);
pthread_mutex_unlock(&mutex);
}
return NULL;
}
int main() {
pthread_t* thread_id;
volatile int i;
int* thread_arr;
printf("
Enter number of threads: ");
scanf("%d", &threads);
// allocate memory to cond (conditional variable) thread id's and array of size threads
cond = (pthread_cond_t*)malloc(sizeof(pthread_cond_t) * threads);
thread_id = (pthread_t*)malloc(sizeof(pthread_t) * threads);
thread_arr = (int*)malloc(sizeof(int) * threads);
for (i = 0; i < threads; i++) { //create threads
thread_arr[i] = i;
pthread_create(&thread_id[i], NULL, sync_thread, (void*)&thread_arr[i]);
}
// waiting for thread
for (i = 0; i < threads; i++) {
pthread_join(thread_id[i], NULL);
}
return 0;
}Output
$ g++ test.cpp -lpthread $ ./a.out Enter number of threads: 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 1 2 3 4 5 ... ... ...
Updated on: 30-Jul-2019
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