getpriority man page on SmartOS

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       getpriority, setpriority - get and set the nice value

       #include <sys/resource.h>

       int getpriority(int which, id_t who);

       int setpriority(int which, id_t who, int value);

       The getpriority() function obtains the nice value of a process, thread,
       or set of processes.  The setpriority() function sets the nice value of
       a  process,  thread, or set of processes to value+NZERO, where NZERO is
       defined to be 20.

       Target entities are specified by the values of the which and who	 argu‐
       ments.	The  which  argument  can  be  one  of	the  following values:
       PRIO_TASK,  PRIO_PROJECT,  PRIO_ZONE, or PRIO_CONTRACT, indicating that
       the who argument is to be interpreted as a process ID, a process	 group
       ID, an effective user ID, an effective group ID, a session ID, a thread
       (lwp) ID, a task ID, a project ID, a zone ID, or a process contract ID,
       respectively.   A  0  value  for the who argument specifies the current
       process, process group, or user. A 0 value  for	the  who  argument  is
       treated	as  valid  group  ID,  session	ID,  thread (lwp) ID, task ID,
       project ID, zone ID, or process contract ID. A P_MYID value for the who
       argument	 can  be  used	to specify the current group, session, thread,
       task, project, zone, or process contract, respectively.

       If a specified process is multi-threaded, the nice value set with  set‐
       priority() affects all threads in the process.

       If more than one process is specified, getpriority() returns NZERO less
       than the lowest nice value pertaining to any of the specified entities,
       and  setpriority()  sets	 the  nice values of all of the specified pro‐
       cesses to value+NZERO.

       The default nice value is NZERO. Lower nice values cause more favorable
       scheduling.  The	 range	of  valid  nice	 values	 is 0 to NZERO*2-1. If
       value+NZERO is less than the system's lowest supported nice value, set‐
       priority()  sets	 the  nice  value  to  the  lowest supported value. If
       value+NZERO is greater than the system's highest supported nice	value,
       setpriority() sets the nice value to the highest supported value.

       Only a process with appropriate privileges can lower the nice value.

       Any  process  or thread using SCHED_FIFO or SCHED_RR is unaffected by a
       call to setpriority(). This is not considered an error.	A  process  or
       thread  that subsequently reverts to SCHED_OTHER will not have its pri‐
       ority affected by such a setpriority() call.

       The effect of changing the nice value varies depending on the  schedul‐
       ing policy in effect.

       Since  getpriority()  can return the value -1 on successful completion,
       it is necessary to set errno to 0 prior to a call to getpriority().  If
       getpriority() returns the value -1, then errno can be checked to see if
       an error occurred or if the value is a legitimate nice value.

       Upon successful completion, getpriority() returns  an  integer  in  the
       range  from  -NZERO to NZERO-1.	Otherwise, −1 is returned and errno is
       set to indicate the error.

       Upon successful completion, setpriority() returns 0. Otherwise,	−1  is
       returned and errno is set to indicate the error.

       The getpriority() and setpriority() functions will fail if:

		 No process or thread could be located using the which and who
		 argument values specified.

		 The value of the which argument was not  recognized,  or  the
		 value	of the who argument is not a valid process ID, process
		 group ID, user ID, group ID, session  ID,  thread  (lwp)  ID,
		 task ID, project ID, or zone ID.

       In addition, setpriority() may fail if:

		 A  process  was  located,  but neither the real nor effective
		 user ID of the executing process match the effective user  ID
		 of the process whose nice value is being changed.

		 A  request  was  made	to  change  the	 nice value to a lower
		 numeric value and the current process does not have appropri‐
		 ate privileges.

       Example 1 Example using getpriority()

       The  following  example returns the current scheduling priority for the
       process ID returned by the call to getpid(2).

	 #include <sys/resource.h>
	 int which = PRIO_PROCESS;
	 id_t pid;
	 int ret;

	 pid = getpid();
	 ret = getpriority(which, pid);

       Example 2 Example using setpriority()

       The following example sets the nice value for the current process to 0.

	 #include <sys/resource.h>
	 int which = PRIO_PROCESS;
	 id_t pid;
	 int value = -20;
	 int ret;

	 pid = getpid();
	 ret = setpriority(which, pid, value);

       The getpriority() and setpriority() functions work with an offset  nice
       value  (value-NZERO).  The  nice	 value is in the range 0 to 2*NZERO-1,
       while the return value for getpriority() and the	 third	parameter  for
       setpriority() are in the range -NZERO to NZERO-1.

       See attributes(5) for descriptions of the following attributes:

       │Interface Stability │ Committed		│
       │Standard	    │ See standards(5). │

       nice(1), renice(1), sched_get_priority_max(3C), sched_setscheduler(3C),
       attributes(5), standards(5)

				  Apr 1, 2008		       GETPRIORITY(3C)

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