Re: Unable set the priority for a pthread through pthread_setschedparam

[Manish Katiyar <mkatiyar@xxxxxxxxx>]

On Tue, Feb 3, 2009 at 10:18 AM, Srinivas G.
<srinivasg@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Dear All,
>
> I have written a small thread program in C using the pthreads. I am able
> to set the threads priority with pthread_setschedparam API when I login
> as ROOT. If I login as a normal user other than ROOT, then the API
> returns the error number 1 (EPERM).
>
> Please let me know whether a normal user can set the pthreads priority
> with pthread_setschedparam API or not.

The man page says it all

              !EPERM!
                     the calling process does not have superuser permissions

you cannot unless you have superuser permissions.

Thanks -
Manish


>
> Here is the sample code for testing.
>
> /*
>  * Creates two threads, one printing 10 "a"s,
>  * the other printing 10 "b"s.
>  * Illustrates: thread creation, thread joining.
>  */
>
> #include <stddef.h>
> #include <stdio.h>
> #include <unistd.h>
> #include "pthread.h"
> #include <errno.h>
>
> void * process(void * arg)
> {
>  int i;
>  fprintf(stderr, "Starting process %s\n", (char *) arg);
>  for (i = 0; i < 10; i++) {
>    write(1, (char *) arg, 1);
>  }
>  fprintf(stderr,"\n");
>
>  return NULL;
> }
>
> int main()
> {
>  int retcode;
>  pthread_t th_a, th_b;
>  void * retval;
>  struct sched_param sp;
>  int esnRetVal = 0;
>  pthread_attr_t attr;
>
>  pthread_attr_init(&attr);
>  pthread_attr_setinheritsched(&attr, PTHREAD_INHERIT_SCHED);
>
>  retcode = pthread_create(&th_a, &attr, process, "a");
>  if (retcode != 0) fprintf(stderr, "create a failed %d\n", retcode);
>
>  sp.sched_priority = 30;
>  esnRetVal = pthread_setschedparam(th_a, SCHED_RR, &sp);
>  if(esnRetVal != 0)
>  {
>     printf("Failed to set the pthread sched param! esnRetVal = %d errno
> = %d\n", esnRetVal, errno);
>     return -1;
>  }
>
>  retcode = pthread_create(&th_b, NULL, process, "b");
>  if (retcode != 0) fprintf(stderr, "create b failed %d\n", retcode);
>
>  retcode = pthread_join(th_a, &retval);
>  if (retcode != 0) fprintf(stderr, "join a failed %d\n", retcode);
>
>  retcode = pthread_join(th_b, &retval);
>  if (retcode != 0) fprintf(stderr, "join b failed %d\n", retcode);
>
>  return 0;
> }
>
> Thanks in advance.
>
> With Regards,
> Srinivas G
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