schedctl_init(3C)					   Standard C Library Functions 					 schedctl_init(3C)

NAME

       schedctl_init, schedctl_lookup, schedctl_exit, schedctl_start, schedctl_stop - preemption control

SYNOPSIS

       cc [ flag... ] file...  [ library... ]
       #include <schedctl.h>

       schedctl_t *schedctl_init(void);

       schedctl_t *schedctl_lookup(void);

       void schedctl_exit(void);

       void schedctl_start(schedctl_t *ptr);

       void schedctl_stop(schedctl_t *ptr);

DESCRIPTION

       These functions provide limited control over the scheduling of a thread (see threads(5)). They allow a running thread to give a hint to the
       kernel that preemptions of that thread should be avoided. The most likely use for these functions is to block preemption  while	holding  a
       spinlock.  Improper  use of this facility, including attempts to block preemption for sustained periods of time, may result in reduced per-
       formance.

       The schedctl_init() function initializes preemption control for the calling thread and returns a pointer used to  refer	to  the  data.	If
       schedctl_init() is called more than once by the same thread, the most recently returned pointer is the only valid one.

       The  schedctl_lookup()  function returns the currently allocated preemption control data associated with the calling thread that was previ-
       ously returned by schedctl_init(). This can be useful in programs where it is difficult to maintain local state for each thread.

       The schedctl_exit() function removes the preemption control data associated with the calling thread.

       The schedctl_start() macro gives a hint to the kernel scheduler that preemption should be avoided on the current thread. The pointer passed
       to  the	macro  must  be the same as the pointer returned by the call to schedctl_init() by the current thread. The behavior of the program
       when other values are passed is undefined.

       The schedctl_stop() macro removes the hint that was set by schedctl_start(). As with schedctl_start(), the pointer passed to the macro must
       be the same as the pointer returned by the call to schedctl_init() by the current thread.

       The  schedctl_start() and schedctl_stop() macros are intended to be used to bracket short critical sections, such as the time spent holding
       a spinlock. Other uses, including the failure to call schedctl_stop() soon after calling schedctl_start(), might  result  in  poor  perfor-
       mance.

RETURN VALUES

       The  schedctl_init()  function  returns	a  pointer  to a schedctl_t structure if the initialization was successful, or NULL otherwise. The
       schedctl_lookup() function returns a pointer to a schedctl_t structure if the data for that thread was found, or NULL otherwise.

ERRORS

       No errors are returned.

ATTRIBUTES

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

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Stable			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |MT-Safe			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       priocntl(1), exec(2), fork(2), priocntl(2), attributes(5), threads(5)

NOTES

       Preemption control is intended for use by threads belonging to the time-sharing (TS), interactive (IA), fair-share (FSS), and  fixed-prior-
       ity  (FX) scheduling classes. If used by threads in other scheduling classes, such as real-time (RT), no errors will be returned but sched-
       ctl_start() and schedctl_stop() will not have any effect.

       The data used for preemption control are not copied in the child of a fork(2). Thus, if a process containing threads using preemption  con-
       trol  calls  fork  and  the  child does not immediately call exec(2), each thread in the child must call schedctl_init() again prior to any
       future uses of schedctl_start() and schedctl_stop(). Failure to do so will result in undefined behavior.

SunOS 5.10							    28 May 2003 						 schedctl_init(3C)