NetBSD/share/man/man9/sleep.9

168 lines
5.5 KiB
Groff
Raw Normal View History

.\" $NetBSD: sleep.9,v 1.7 1997/11/05 12:13:44 mrg Exp $
1996-06-23 18:04:43 +04:00
.\"
.\" Copyright (c) 1996 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Paul Kranenburg.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the NetBSD
.\" Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\" contributors may be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
1996-06-23 18:04:43 +04:00
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd June 23, 1996
.Dt SLEEP 9
.Os NetBSD
.Sh NAME
.Nm sleep ,
.Nm tsleep ,
.Nm wakeup
.Nd process context sleep and and wakeup
1996-06-23 18:04:43 +04:00
.Sh SYNOPSIS
.Ft int
.Fn "tsleep" "void *ident" "int priority" "char *wmesg" "int timo"
1996-06-23 18:04:43 +04:00
.Ft void
.Fn "sleep" "void *ident" "int priority"
1996-06-23 18:04:43 +04:00
.Ft void
.Fn "wakeup" "void *ident"
.Sh DESCRIPTION
These functions implement voluntary context switching.
.Fn tsleep
and
.Fn sleep
are used throughout the kernel whenever processing in the current context
can not continue for any of the following reasons:
.Bl -bullet -offset indent
.It
The current process needs to await the results of a pending I/O operation.
.It
The current process needs resources
.Pq e.g. memory
which are temporarily unavailable.
.It
The current process wants access to data-structures which are locked by
other processes.
.El
.Pp
The function
.Fn wakeup
is used to notify sleeping processes of possible changes to the condition
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
.Dq blocking
condition has cleared.
.Pp
The
.Fn tsleep
function takes the following arguments:
.Bl -tag -width priority
.It Fa ident
1996-06-23 18:04:43 +04:00
An identifier of the
.Dq wait channel
representing the resource for which the current process needs to wait. This
1996-06-23 18:04:43 +04:00
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
1996-06-23 18:04:43 +04:00
.Fn wakeup
to get the process going again.
.Fa ident
should not be
.Dv NULL .
.It Fa priority
The process priority to be used when the process is awakened and put on
1996-11-19 01:16:50 +03:00
the queue of runnable processes. This mechanism is used to optimize
1996-06-23 18:04:43 +04:00
.Dq throughput
of processes executing in kernel mode. If the flag
.Dv PCATCH
is OR'ed into
.Fa priority
the process checks for posted signals before and after sleeping.
.It Fa 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
.Pq through the process structure field Li p_wmesg
for user level utilities such as
.Xr ps 1 .
.It Fa timo
If non-zero, the process will sleep for at most
.Li timo/hz
seconds. If this amount of time elapses and no
.Fn wakeup "ident"
has occurred, and no signal
.Pq if Dv PCATCH No was set
1996-06-23 18:04:43 +04:00
was posted,
.Fn tsleep
will return
.Er EWOULDBLOCK .
.El
.Pp
The
.Fn sleep
function puts the process in an uninterruptable sleep. It is functionally
equivalent to:
.Bd -literal -offset indent
tsleep(ident, priority & PRIMASK, 0, 0)
.Ed
.Pp
The
.Fn wakeup
function will mark all processes which are currently sleeping on the identifier
.Fa ident
as runnable. Eventually, each of the processes will resume execution in
the kernel context, causing a return from
.Fn [t]sleep .
Note that processes returning from sleep should always re-evaluate the
conditions that blocked them, since a call to
.Fn wakeup
merely signals a
.Em possible
change to the blocking conditions. For example, when two or more processes
are waiting for an exclusive lock, only one of them will succeed in acquiring
the lock when it is released. All others will have to go back to sleep and
1996-11-19 01:16:50 +03:00
wait for the next opportunity.
1996-06-23 18:04:43 +04:00
.Sh RETURN VALUES
.Fn tsleep
returns 0 if it returns as a result of a
1996-06-23 18:04:43 +04:00
.Fn wakeup .
If a
1997-09-21 18:35:00 +04:00
.Fn tsleep
1996-06-23 18:04:43 +04:00
returns as a result of a signal, the return value is
.Er ERESTART
if the signal has the
.Dv SA_RESTART
property
.Pq see Xr sigaction 2 ,
and
1996-06-23 18:04:43 +04:00
.Er EINTR
otherwise.
If
.Fn tsleep
returns because of a timeout it returns
.Er EWOULDBLOCK .