Print 1 2 3 infinitely using thread. Create three threads viz T1, T2, and T3 such that those should print 1 2 3 sequence infinitely.
Examples :
Output :1 2 3 1 2 3 1 2 3 1 2 3 1 2 3 ......
Prerequisite : Threads in C
Approach :
- Start an infinite loop and initialize a variable ‘done’ to 1.
- Now, check for the value of done is not equal to 1.
- If it is hold wait condition lock, else print n and respectively signal the next consecutive n.
// C code to print 1 2 3 infinitely using pthread #include <stdio.h> #include <pthread.h> // Declaration of thread condition variables pthread_cond_t cond1 = PTHREAD_COND_INITIALIZER;
pthread_cond_t cond2 = PTHREAD_COND_INITIALIZER;
pthread_cond_t cond3 = PTHREAD_COND_INITIALIZER;
// mutex which we are going to // use avoid race condition. pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER; // done is a global variable which decides // which waiting thread should be scheduled int done = 1;
// Thread function void *foo( void *n)
{ while (1) {
// acquire a lock
pthread_mutex_lock(&lock);
if (done != ( int )*( int *)n) {
// value of done and n is not equal,
// hold wait lock on condition variable
if (( int )*( int *)n == 1) {
pthread_cond_wait(&cond1, &lock);
} else if (( int )*( int *)n == 2) {
pthread_cond_wait(&cond2, &lock);
}
else {
pthread_cond_wait(&cond3, &lock);
}
}
// done is equal to n, then print n
printf ( "%d " , *( int *)n);
// Now time to schedule next thread accordingly
// using pthread_cond_signal()
if (done == 3) {
done = 1;
pthread_cond_signal(&cond1);
}
else if (done == 1) {
done = 2;
pthread_cond_signal(&cond2);
} else if (done == 2) {
done = 3;
pthread_cond_signal(&cond3);
}
// Finally release mutex
pthread_mutex_unlock(&lock);
}
return NULL;
} // Driver code int main()
{ pthread_t tid1, tid2, tid3;
int n1 = 1, n2 = 2, n3 = 3;
// Create 3 threads
pthread_create(&tid1, NULL, foo, ( void *)&n1);
pthread_create(&tid2, NULL, foo, ( void *)&n2);
pthread_create(&tid3, NULL, foo, ( void *)&n3);
// infinite loop to avoid exit of a program/process
while (1);
return 0;
} |
Output :
1 2 3 1 2 3 1 2 3 1 2 3 ...