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

     sleep, msleep, tsleep, wakeup -- wait for events

     #include <sys/param.h>
     #include <sys/systm.h>
     #include <sys/proc.h>

     tsleep(void *ident, int priority, const char *wmesg, int timo);

     msleep(void *ident, struct	mtx *mtx, int priority,	const char *wmesg,
	 int timo);

     wakeup(void *ident);

     wakeup_one(void *ident);

     The functions tsleep() and	wakeup() handle	event-based process blocking.
     If	a process must wait for	an external event, it is put on	sleep by
     tsleep.  The parameter ident is an	arbitrary address that uniquely	iden-
     tifies the	event on which the process is being asleep.  All processes
     sleeping on a single ident	are woken up later by wakeup, often called
     from inside an interrupt routine, to indicate that	the resource the
     process was blocking on is	available now.

     The parameter wmesg is a string describing	the sleep condition for	tools
     like ps(1).  Due to the limited space of those programs to	display	arbi-
     trary strings, this message should	not be longer than 6 characters.

     The wakeup_one() function is used to make the first process in the	queue
     that is sleeping on the parameter ident runnable.	This can prevent the
     system from becoming saturated when a large number	of processes are
     sleeping on the same address, but only one	of them	can actually do	any
     useful work when made runnable.

     Tsleep is the general sleep call.	Suspends the current process until a
     wakeup is performed on the	specified identifier.  The process will	then
     be	made runnable with the specified priority.  Sleeps at most timo	/ hz
     seconds (0	means no timeout).  If pri includes the	PCATCH flag, signals
     are checked before	and after sleeping, else signals are not checked.  Re-
     turns 0 if	awakened, EWOULDBLOCK if the timeout expires.  If PCATCH is
     set and a signal needs to be delivered, ERESTART is returned if the cur-
     rent system call should be	restarted if possible, and EINTR is returned
     if	the system call	should be interrupted by the signal (return EINTR).

     Msleep is a variation on tsleep.  The parameter mtx is a mutex, which
     will be exited before sleeping, and entered before	msleep returns.	 If
     pri includes the PDROP flag, the mtx parameter will not be	entered	before
     returning.	 The mutex is used to ensure that a condition can be checked
     atomically, and that the current process can be suspended without missing
     a change to the condition,	or an associated wakeup.

     See above.

     ps(1), malloc(9), mi_switch(9)

     The sleep/wakeup process synchronization mechanism	is very	old.  It ap-
     peared in a very early version of UNIX.

     Tsleep appeared in	4.4BSD.

     Sleep used	to be the traditional form.  It	doesn't	let you	specify	a
     timeout or	a wmesg, hence it has been discontinued.

     This man page was written by Jorg Wunsch.

BSD			       December	17, 1998			   BSD


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