Pthread_setaffinity_np invalid argument

Question

I am trying to change the affinity of each thread inside the start routine.

Here's the code. In the below code, 't' is the argument passed through the pthread_create function.

    cpu_set_t mask;
    pthread_t c;

    a = *((int *)t);

    printf(" thread no. is %d \n",a);

    CPU_ZERO(&mask);

    a =a/2 + 1;

    CPU_SET(a,&mask);

    c=pthread_self();
    s=pthread_setaffinity_np(c,sizeof(cpu_set_t), &mask);
    if (s!=0)
        handle_error_en(s,"pthread_setaffinity_np");

The thread affinity is not getting changed. Where am I going wrong?

You can replace the entire switch statement with `CPU_SET((a/2+1), &mask);`, by the way. — Daniel Fischer, Jan 16 '12 at 21:57
Perhaps better, to be sure it's evaluated only once, `a = a/2+1; CPU_SET(a, &mask);`. — Daniel Fischer, Jan 16 '12 at 22:05
Is there the slightest possibility that `a` is not in the range 0-15? — Daniel Fischer, Jan 16 '12 at 22:07
I changed the question. Thanks. This is how I am getting the value of 'a' - for (i=0; i<16; i++) { pthread_create(__,__,__,&i); } — akhil28288, Jan 16 '12 at 22:16
You're passing the same int pointer to all the threads, which all dereference it some time later, after the int has changed. — bk1e, Jan 17 '12 at 03:00
Also, maybe the function that created the threads returns before they read the int, and something else uses the same stack location. — bk1e, Jan 17 '12 at 03:03

score 1 · Accepted Answer · answered Jan 31 '12 at 22:13

1

I had misunderstood the bounds of the mask. That was where I was going wrong.

answered Jan 31 '12 at 22:13

akhil28288

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Pthread_setaffinity_np invalid argument

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