iwm: Fix S:N reporting in ifconfig(8)

[dragonfly.git] / share / man / man9 / sleep.9

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.\" Copyright (c) 1996 Joerg Wunsch
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.\" $FreeBSD: src/share/man/man9/sleep.9,v 1.18.2.5 2001/12/17 11:30:19 ru Exp $
.\"
.Dd October 12, 2012
.Dt SLEEP 9
.Os
.Sh NAME
.Nm tsleep ,
.Nm ssleep ,
.Nm lksleep ,
.Nm mtxsleep ,
.Nm zsleep ,
.Nm tsleep_interlock ,
.Nm wakeup ,
.Nm wakeup_one
.Nd wait/sleep/block for events
.Sh SYNOPSIS
.In sys/param.h
.In sys/serialize.h
.In sys/systm.h
.In sys/proc.h
.Ft int
.Fn tsleep "const volatile void *ident" "int flags" "const char *wmesg" "int timo"
.Ft int
.Fn ssleep "const volatile void *ident" "struct spinlock *spin" "int flags" "const char *wmesg" "int timo"
.Ft int
.Fn lksleep "const volatile void *ident" "struct lock *lock" "int flags" "const char *wmesg" "int timo"
.Ft int
.Fn mtxsleep "const volatile void *ident" "struct mtx *mtx" "int flags" "const char *wmesg" "int timo"
.Ft int
.Fn zsleep "const volatile void *ident" "struct lwkt_serialize *slz" "int flags" "const char *wmesg" "int timo"
.Ft void
.Fn tsleep_interlock "const volatile void *ident" "int flags"
.Ft void
.Fn wakeup "const volatile void *ident"
.Ft void
.Fn wakeup_one "const volatile void *ident"
.Sh DESCRIPTION
The functions
.Fn tsleep ,
.Fn ssleep ,
.Fn lksleep ,
.Fn mtxsleep ,
.Fn zsleep ,
and
.Fn wakeup
handle event-based process blocking.
If a process must wait for an
external event, it is put on sleep by
.Fn tsleep ,
.Fn ssleep ,
.Fn lksleep ,
.Fn mtxsleep ,
or
.Fn zsleep .
.Pp
The parameter
.Ar ident
is an arbitrary address that uniquely identifies the event on which
the process is being asleep.
All processes sleeping on a single
.Fa ident
are woken up later by
.Fn wakeup ,
often called from inside an interrupt routine, to indicate that the
resource the process/thread was blocking on is available now.
.Pp
The parameter
.Fa wmesg
is a string describing the sleep condition for tools like
.Xr ps 1 .
Due to the limited space of those programs to display arbitrary strings,
this message should not be longer than 6 characters.
.Pp
The
.Fn tsleep
function is general in its use and suspends the current process/thread until a
wakeup is performed on the specified identifier.
The process/thread will then be made runnable.
The process/thread will sleep at most
.Fa timo
\&/ hz seconds (0 means no timeout).
If
.Fa flags
contains the
.Dv PCATCH
flag, signals are checked before and after sleeping, else signals are
ignored.
.Pp
The
.Fn tsleep_interlock
function is similar to
.Fn tsleep ,
in that it queues a thread on a sleep queue, but it does not actually put the
thread to sleep.
This allows coupling tsleep with higher-level synchronization primitives.
The pattern is:
.Bd -literal
(acquire high level synchronization primitive)
(test condition of interest)
tsleep_interlock(ident, flags)
(release high level synchronization primitive)
tsleep(..., flags | PINTERLOCKED, ...)
.Ed
.Pp
For example, to implement
.Fn ssleep :
.Bd -literal
spin_lock(&important_lock);
if (important_condition == 0) {
	tsleep_interlock(ident, flags);
	spin_unlock(&important_lock);
	tsleep(..., flags | PINTERLOCKED, ...);
}
.Ed
.Pp
The
.Fn ssleep
function works like
.Fn tsleep
while at the same time releasing the exclusive spinlock
.Fa spin
before sleeping and reacquiring it before
.Fn ssleep
returns.
This is an atomic operation, which guarantees that a
.Fn wakeup
interlocked by
.Fa spin
will not be missed.
.Pp
The
.Fn lksleep
function works like
.Fn tsleep
while at the same time releasing the exclusive lockmgr lock
.Fa lock
before sleeping and reacquiring it before
.Fn lksleep
returns.
This is an atomic operation, which guarantees that a
.Fn wakeup
interlocked by
.Fa lock
will not be missed.
.Pp
The
.Fn mtxsleep
function works like
.Fn tsleep
while at the same time atomically releasing the mutex
.Fa mtx
before sleeping and reacquiring it in exclusive state before
.Fn mtxsleep
returns.
.Pp
The
.Fn zsleep
function works like
.Fn tsleep
while at the same time releasing the serializer
.Fa slz
before sleeping and reacquiring it before
.Fn zsleep
returns.
This is an atomic operation, which guarantees that a
.Fn wakeup
interlocked by
.Fa slz
will not be missed.
.Pp
The
.Fn wakeup_one
function is used to make the first process/thread in the queue that is
sleeping on the parameter
.Fa ident
runnable.
This can prevent the system from becoming saturated
when a large number of processes/threads are sleeping on the same address,
but only one of them can actually do any useful work when made
runnable.
.Sh IMPLEMENTATION NOTES
Unlike
.Fx ,
the
.Fn tsleep
function in
.Dx
ignores priority information because it is not required by the
.Tn LWKT
subsystem.
Sleeps without the
.Dv LWP_SINTR
flag set are assumed to be disk-waits, otherwise they are
normal sleeps.
.Sh RETURN VALUES
The
.Fn tsleep
function returns
.Li 0
if awakened, otherwise an appropriate error code is returned.
.Sh FILES
The various sleep functions are in
.Pa /sys/kern/kern_synch.c .
.Sh ERRORS
.Bl -tag -width Er
.It Bq Er EWOULDBLOCK
The timeout expired.
.It Bq Er ERESTART
A signal needs to be delivered and the system call should
be restarted if possible.
This only happens if
.Dv PCATCH
was set in
.Fa flags .
.It Bq Er EINTR
The system call needs to be interrupted by the signal.
This only happens if
.Dv PCATCH
was set in
.Fa flags .
.El
.Sh SEE ALSO
.Xr ps 1 ,
.Xr kmalloc 9 ,
.Xr serializer 9
.Sh HISTORY
The sleep/wakeup process synchronization mechanism is very old.
It appeared in a very early version of Unix.
.Pp
.Fn tsleep
appeared in
.Bx 4.4 .
.Pp
.Fn ssleep
appeared in
.Dx 1.6 ,
.Fn zsleep
in
.Dx 2.0 ,
and
.Fn lksleep
and
.Fn mtxsleep
in
.Dx 2.3 .
.Sh AUTHORS
.An -nosplit
This manual page was written by
.An J\(:org Wunsch
and modified for
.Dx
by
.An Hiten Pandya Aq Mt hmp@dragonflybsd.org .