nice()

Change the priority of a process

Synopsis:

#include <unistd.h>

int  nice( int incr );

Arguments:

incr: The amount that you want to add to the process's priority.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The nice() function allows a process to change its priority. The invoking process must be in a scheduling class that supports the operation.

Note: This function has no effect in any of the scheduling policies that QNX Neutrino supports. Use sched_setparam(), pthread_setschedparam(), or pthread_setschedprio() instead of this function.

The nice() function adds the value of incr to the nice value of the calling process. A process's nice value is a nonnegative number; a greater positive value results in a lower CPU priority.

A maximum nice value of 2 * NZERO - 1 and a minimum nice value of 0 are imposed by the system. NZERO is defined in <limits.h> with a default value of 20. If you request a value above or below these limits, the nice value is set to the corresponding limit. A nice value of 40 is treated as 39. Only a process with superuser privileges can lower the nice value.

Returns:

The new nice value minus NZERO. If an error occurred, -1 is returned, the process's nice value isn't changed, and errno is set.

Errors:

EINVAL: The nice() function was called by a process in a scheduling class other than time-sharing.
EPERM: The incr argument was negative or greater than 40, and the effective user ID of the calling process isn't the superuser.

Classification:

POSIX 1003.1 XSI

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	Yes
Thread	Yes

Caveats:

As -1 is a permissible return value in a successful situation, an application wishing to check for error situations should set errno to 0, then call nice(), and if it returns -1, check to see if errno is nonzero.