GETPRIORITY(2) System Calls Manual GETPRIORITY(2)

getpriority, setpriority — get/set program scheduling priority

#include <sys/resource.h>

int
getpriority(int which, id_t who);

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

The scheduling priority of the process, process group, or user as indicated by which and who is obtained with the () call and set with the setpriority() call. Which is one of PRIO_PROCESS, PRIO_PGRP, or PRIO_USER, and who is interpreted relative to which (a process identifier for PRIO_PROCESS, process group identifier for PRIO_PGRP, and a user ID for PRIO_USER). A zero value of who denotes the current process, process group, or user. prio is a value in the range -20 to 20. The default priority is 0; lower priorities cause more favorable scheduling.

The () call returns the highest priority (lowest numerical value) enjoyed by any of the specified processes. The setpriority() call sets the priorities of all of the specified processes to the specified value. Only the super-user may lower priorities.

Additionally, the current thread or process can be placed in a background state by specifying PRIO_DARWIN_THREAD or PRIO_DARWIN_PROCESS for which. Only a value of zero (the current thread or process) is supported for who when setting or getting background state. prio is either 0 (to remove current thread from background status) or PRIO_DARWIN_BG (to set current thread into background state). When a thread or process is in a background state the scheduling priority is set to the lowest value, disk IO is throttled (with behavior similar to using setiopolicy_np(3) to set a throttleable policy), and network IO is throttled for any sockets opened after going into background state. Any previously opened sockets are not affected. The () call returns 0 when current thread or process is not in background state or 1 when the current thread is in background state. Any thread or process can set itself into background state.

Since getpriority() can legitimately return the value -1, it is necessary to clear the external variable errno prior to the call, then check it afterward to determine if a -1 is an error or a legitimate value. The setpriority() call returns 0 if there is no error, or -1 if there is.

getpriority() and setpriority() will fail if:

[]
Which is not one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, PRIO_DARWIN_THREAD, or PRIO_DARWIN_PROCESS.
[]
Who is not a valid process, process group, or user ID.
[]
Who is not 0 when which is PRIO_DARWIN_THREAD or PRIO_DARWIN_PROCESS.
[]
No process can be located using the which and who values specified.

In addition to the errors indicated above, setpriority() will fail if:

[]
A non super-user attempts to lower a process priority.
[]
A process is located, but neither its effective nor real user ID matches the effective user ID of the caller.

#include <sys/types.h> #include <sys/resource.h>

The include file <sys/types.h> is necessary.

int
(int which, int who);;

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

The type of who has changed.

nice(1), fork(2), setiopolicy_np(3), compat(5), renice(8)

The getpriority() function call appeared in 4.2BSD.

June 4, 1993 BSD 4