Linux调度。 （p线程）

Question

I'm trying to play around with threads and so far, with the code below, I'm doing fine. I want also want to print the current index of the executing thread but I've encountered some problems.

#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5

void *runner(void *param);

int main(int argc, char *argv[])
{
    int i, policy;
    pthread_t tid[NUM_THREADS];
    pthread_attr_t attr;

    pthread_attr_init(&attr);

    if(pthread_attr_getschedpolicy(&attr, &policy) != 0)
        fprintf(stderr, "Unable to get policy.\n");
    else{
        if(policy == SCHED_OTHER)
            printf("SCHED_OTHER\n");
        else if(policy == SCHED_RR)
            printf("SCHED_RR\n");
        else if(policy == SCHED_FIFO)
            printf("SCHED_FIFO\n");
    }

    if(pthread_attr_setschedpolicy(&attr, SCHED_FIFO) != 0)
        fprintf(stderr, "Unable to set policy.\n");
    /* create the threads */
    for(i = 0; i < NUM_THREADS; i++)
        printf("Hi, I'm thread #%d\n", i);
        pthread_create(&tid[i], &attr, runner, NULL);
    /* now join on each thread */
    for(i = 0; i < NUM_THREADS; i++)
        pthread_join(tid[i], NULL);
}

/* Each thread will begin control in this function */
void *runner(void *param)
{
     /* do some work... */
     printf("Hello world!");
     pthread_exit(0);
}

I'm trying to print the current executing thread along with "Hello world!". But, the output is this...

SCHED_OTHER
Hello, I'm thread #0
Hello, I'm thread #1
Hello, I'm thread #2
Hello, I'm thread #3
Hello, I'm thread #4
Segmentation fault (core dumped)

So far, I've already tried issuing

ulimit -c unlimited

What can I tweak in the code to achieve my goal?

Answer 1

This

  for(i = 0; i < NUM_THREADS; i++)
        printf("Hi, I'm thread #%d\n", i);
        pthread_create(&tid[i], &attr, runner, NULL);

should be

  for(i = 0; i < NUM_THREADS; i++) {
        printf("Hi, I'm thread #%d\n", i);
        pthread_create(&tid[i], &attr, runner, NULL);
   }

In your code, you are just creating only one thread and attempting to join 5 threads.

Answer 2

You forgot to put a block of statements in braces:

for(i = 0; i < NUM_THREADS; i++)
    printf("Hi, I'm thread #%d\n", i);
    pthread_create(&tid[i], &attr, runner, NULL);

Multiple statements to be executed in for loop must be covered in braces otherwise only first of them is called, printf("Hi, I'm thread #%d\\n", i) in this case. Solution:

for(i = 0; i < NUM_THREADS; i++)
{
    printf("Hi, I'm thread #%d\n", i);
    pthread_create(&tid[i], &attr, runner, NULL);
}