[Buildroot] nice() seems to have stopped working?

[Buildroot] nice() seems to have stopped working?

[David Lambert]

Since moving to this distribution, I notice that some of my programs 
that use nice() give errors when attempting to raise their priorities. 
In order to try and nail this down I wrote the following trivial program:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

int	main(int ac, char *av[])
{
   int n    printf("Trying nice(%d)\n", n);
   if (nice(n) < 0) {		/* Attempt to change priority */
     perror("Nice failed to change priority");
   }
   else {
     printf("Success\n");
   }
   return 0;
}


Running this program as root provides the following output:

/ # whoami
root
/ # niceTest 0
Trying nice(0)
Success
/ # niceTest 1
Trying nice(1)
Success
/ # niceTest -1
Trying nice(-1)
Nice failed to change priority: Success
/ #

Has anyone else experience this behavior?

Best regards,

Dave.
-------------- next part --------------
A non-text attachment was scrubbed...
Name: dave.vcf
Type: text/x-vcard
Size: 288 bytes
Desc: not available
Url : http://busybox.net/lists/buildroot/attachments/20061018/fd7b7bf5/attachment.vcf 

[Buildroot] nice() seems to have stopped working?

[Bernhard Fischer]

On Wed, Oct 18, 2006 at 01:09:30PM -0500, David Lambert wrote:
>Since moving to this distribution, I notice that some of my programs 
>that use nice() give errors when attempting to raise their priorities. 
>In order to try and nail this down I wrote the following trivial program:
>
>#include <stdio.h>
>#include <stdlib.h>
>#include <string.h>
>#include <unistd.h>
>
>int	main(int ac, char *av[])
>{
>  int n = atoi(av[1]);
>  printf("Trying nice(%d)\n", n);
>  if (nice(n) < 0) {		/* Attempt to change priority */
>    perror("Nice failed to change priority");
>  }
>  else {
>    printf("Success\n");
>  }
>  return 0;
>}
>
>
>Running this program as root provides the following output:
>
>/ # whoami
>root
>/ # niceTest 0
>Trying nice(0)
>Success
>/ # niceTest 1
>Trying nice(1)
>Success
>/ # niceTest -1
>Trying nice(-1)
>Nice failed to change priority: Success
>/ #
>
>Has anyone else experience this behavior?
>
>Best regards,
>
>Dave.

hm?

See man 2 nice
[snip]
NOTES
       SUSv2 and POSIX.1-2001 specify that nice() should return the  new nice
       value.  However, the Linux syscall and the nice() library function pro-
       vided in older versions of (g)libc (earlier than glibc 2.2.4) return  0
       on success.  The new nice value can be found using getpriority(2).

       Since  glibc  2.2.4,  nice()  is implemented as a library function that
       calls getpriority(2) to obtain the new nice value to be returned to the
       caller.   With  this implementation, a successful call can legitimately
       return -1.  To reliably detect an error, set  errno  to  0 before  the
       call, and check its value when nice() returns -1.


PS: See uClibc/libc/sysdeps/linux/common/nice.c for the gory details.
HTH,