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NetBSD 6.1.5 - man page for ltsleep (netbsd section 9)

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

NAME
     ltsleep, tsleep, wakeup -- process context sleep and wakeup

SYNOPSIS
     #include <sys/proc.h>

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

     void
     wakeup(wchan_t ident);

DESCRIPTION
     The interfaces described in this manual page are obsolete and will be removed from a future
     version of the system.

     The ltsleep() interface has been obsoleted and removed from the system.

     Please see the condvar(9), mutex(9), and rwlock(9) manual pages for information on kernel
     synchronisation primitives.

     These functions implement voluntary context switching.  tsleep() is used throughout the ker-
     nel whenever processing in the current context can not continue for any of the following
     reasons:

	   o   The current process needs to await the results of a pending I/O operation.

	   o   The current process needs resources (e.g., memory) which are temporarily unavail-
	       able.

	   o   The current process wants access to data-structures which are locked by other pro-
	       cesses.

     The function wakeup() is used to notify sleeping processes of possible changes to the condi-
     tion that caused them to go to sleep.  Typically, an awakened process will -- after it has
     acquired a context again -- retry the action that blocked its operation to see if the
     ``blocking'' condition has cleared.

     The tsleep() function takes the following arguments:

     ident     An identifier of the ``wait channel'' representing the resource for which the cur-
	       rent process needs to wait.  This typically is the virtual address of some kernel
	       data-structure related to the resource for which the process is contending.  The
	       same identifier must be used in a call to wakeup() to get the process going again.
	       ident should not be NULL.

     priority  The process priority to be used when the process is awakened and put on the queue
	       of runnable processes.  This mechanism is used to optimize ``throughput'' of pro-
	       cesses executing in kernel mode.  If the flag PCATCH is OR'ed into priority the
	       process checks for posted signals before and after sleeping.

     wmesg     A pointer to a character string indicating the reason a process is sleeping.  The
	       kernel does not use the string, but makes it available (through the process
	       structure field p_wmesg) for user level utilities such as ps(1).

     timo      If non-zero, the process will sleep for at most timo/hz seconds.  If this amount
	       of time elapses and no wakeup(ident) has occurred, and no signal (if PCATCH was
	       set) was posted, tsleep() will return EWOULDBLOCK.

     The wakeup() function will mark all processes which are currently sleeping on the identifier
     ident as runnable.  Eventually, each of the processes will resume execution in the kernel
     context, causing a return from tsleep().  Note that processes returning from sleep should
     always re-evaluate the conditions that blocked them, since a call to wakeup() merely signals
     a possible change to the blocking conditions.  For example, when two or more processes are
     waiting for an exclusive-access lock (see lock(9)), only one of them will succeed in acquir-
     ing the lock when it is released.	All others will have to go back to sleep and wait for the
     next opportunity.

RETURN VALUES
     tsleep() returns 0 if it returns as a result of a wakeup().  If a tsleep() returns as a
     result of a signal, the return value is ERESTART if the signal has the SA_RESTART property
     (see sigaction(2)), and EINTR otherwise.  If tsleep() returns because of a timeout it
     returns EWOULDBLOCK.

SEE ALSO
     sigaction(2), condvar(9), hz(9), lock(9), mutex(9), rwlock(9)

HISTORY
     The sleep/wakeup process synchronization mechanism is very old.  It appeared in a very early
     version of Unix.  tsleep() appeared in 4.4BSD.  ltsleep() appeared in NetBSD 1.5.

BSD					 January 28, 2012				      BSD
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