yield(9) [netbsd man page]

PREEMPT(9)						   BSD Kernel Developer's Manual						PREEMPT(9)

NAME

     preempt, yield -- general preempt and yield functions

SYNOPSIS

     #include <sys/sched.h>

     void
     preempt(void);

     #include <sys/proc.h>

     void
     yield(void);

DESCRIPTION

     The preempt() function puts the current LWP back on the system run queue and performs an involuntary context switch.  The yield() function is
     mostly same as preempt(), except that it performs a voluntary context switch.

     These functions drop the kernel lock before switching and re-acquire it before returning.

BSD
								   July 3, 2007 							       BSD

USERRET(9)						   BSD Kernel Developer's Manual						USERRET(9)

NAME

     userret -- return path to user-mode execution

SYNOPSIS

     #include <sys/lwp.h>
     #include <sys/sched.h>

     void
     userret(struct lwp *l);

DESCRIPTION

     The userret() function is executed after processing a trap (e.g., a system call or interrupt) before returning to user-mode execution.  The
     implementation is machine dependent and is never invoked from machine-independent code.  The function prototype for each architecture may be
     different to the prototype above, however the functionally provided by the userret() function on each architecture is essentially the same.

     Specifically, the userret() function performs the following procedure:

	   o   Detect a change in the signal disposition of the current process and invoke postsig(9) to post the signal to the process.  This may
	       occur when the outcome of the trap or syscall posted a signal to the process (e.g., invalid instruction trap).

	   o   Check the want_resched flag to see if the scheduler requires the current process to be preempted by invoking preempt(9) (see
	       cpu_need_resched(9)).  This may occur if the clock interrupt causes the scheduler to determine that the current process has com-
	       pleted its time slice.

	   o   Update the scheduler state.

SEE ALSO

     cpu_need_resched(9), postsig(9), preempt(9), scheduler(9)

BSD
								 December 20, 2005							       BSD