Running multiple thread with round-robin scheduling-CodePudding

I'm quite new to multi-threading programming. I want to write a code with 3 different threads, each of which prints some different characters. The execution of the threads should be based on a round-robin algorithm. Suppose we have t1, t2, and t3 threads, their execution sequence should be like t1, t2, t3, t1, t2, t3,...

I write the following code for this purpose:

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

void* a(void* ptr) {
    for (int i=0; i< 10; i  ){
        printf("1");
        printf("2");
        printf("3");
        printf("4");
    }
    return NULL;
}

void* b(void* ptr) {
    for (int i=0; i< 10; i  ){
        printf("a");
        printf("b");
        printf("c");
        printf("d");
    }
    return NULL;
}

void* c(void* ptr) {
    for (int i=0; i< 10; i  ){
        printf("5");
        printf("6");
        printf("7");
        printf("8");
    }
    return NULL;
}

int main() {
    pthread_attr_t attr1, attr2, attr3;
    
    pthread_attr_init(&attr1);
    pthread_attr_init(&attr2);
    pthread_attr_init(&attr3);
    
    pthread_t t1, t2, t3;
    
    pthread_attr_setschedpolicy(&attr1, SCHED_RR);
    pthread_create(&t1, &attr1, a, NULL);
    
    pthread_attr_setschedpolicy(&attr2, SCHED_RR);
    pthread_create(&t2, &attr2, b, NULL);
    
    pthread_attr_setschedpolicy(&attr3, SCHED_RR);
    pthread_create(&t3, &attr3, c, NULL);
    
    pthread_join(t1, NULL);
    pthread_join(t2, NULL);
    pthread_join(t3, NULL);
    
    pthread_exit(0);
    return 0;
}

And the output is:

First of all: the output is not reproducible, every time I run the binary file I get different output.

12341234123412341234156785678567856785678567856785678567856782341234123412341234abcdabcdabcdabcdabcdabcdabcdabcdabcdabcd.

My desired output is something like this:

123abc567...

Does everybody know what the problem is with my code?

Thanks

CodePudding user response：

How can I ensure that my threads are being executed in the Round-robin scheduling policy?

You're almost there. You ensure it by calling

Unfortunately, the Posix Threads Library (pthreads) doesn't provide any easy-to-use semaphore, and Unix semaphores aren't exactly trivial to use.

IMO, you should do a little research, and then come back and ask a new question if you encounter anything that you don't understand.