getpriority(2) BSD 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 indi- cated by which and who is obtained with the getpriority() call and set with the setpriority() call. Additionally, the current thread can be set to background state. Which is one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, or PRIO_DARWIN_THREAD, 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, user, thread (for PRIO_DARWIN_THREAD). prio is a value in the range -20 to 20. The default priority is 0; lower priorities cause more favorable scheduling. For PRIO_DARWIN_THREAD, prio is either 0 (to remove current thread from background status) or PRIO_DARWIN_BG (to set current thread into background state). The getpriority() call returns the highest priority (lowest numerical value) enjoyed by any of the specified processes or for PRIO_DAR- WIN_THREAD returns 0 when current thread is not in background state or 1 when the current thread is in background state. The setpriority() call sets the priorities of all of the specified processes to the specified value. When setting a thread into background state the scheduling prior- ity is set to lowest value, disk and network IO are throttled. Network IO will be throttled for any sockets the thread opens after going into background state. Any previously opened sockets are not affected. Only the super-user may lower priorities, but any thread 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: [EINVAL] Which is not one of PRIO_PROCESS, PRIO_PGRP, PRIO_USER, or PRIO_DARWIN_THREAD. [EINVAL] Who is not a valid process, process group, or user ID. [EINVAL] Who is not 0 when which is PRIO_DARWIN_THREAD. [ESRCH] No process can be located using the which and who val- ues specified. In addition to the errors indicated above, setpriority() will fail if: [EACCES] A non super-user attempts to lower a process priority. [EPERM] 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 getpriority(int which, int who); int setpriority(int which, int who, int value); The type of who has changed.
The getpriority() function call appeared in 4.2BSD. 4th Berkeley Distribution June 4, 1993 4th Berkeley Distribution
Mac OS X 10.7 - Generated Mon Nov 7 05:35:57 CST 2011