297 lines
8.9 KiB
Groff
297 lines
8.9 KiB
Groff
.\" Copyright (c) 2000-2004 John H. Baldwin <jhb@FreeBSD.org>
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" 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.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``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 DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
|
|
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR 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.
|
|
.\"
|
|
.\" $FreeBSD$
|
|
.\"
|
|
.Dd March 10, 2004
|
|
.Dt SLEEPQUEUE 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm init_sleepqueues ,
|
|
.Nm sleepq_abort ,
|
|
.Nm sleepq_add ,
|
|
.Nm sleepq_alloc ,
|
|
.Nm sleepq_broadcast ,
|
|
.Nm sleepq_calc_signal_retval ,
|
|
.Nm sleepq_catch_signals ,
|
|
.Nm sleepq_free ,
|
|
.Nm sleepq_lookup ,
|
|
.Nm sleepq_release ,
|
|
.Nm sleepq_remove ,
|
|
.Nm sleepq_signal ,
|
|
.Nm sleepq_set_timeout ,
|
|
.Nm sleepq_timedwait ,
|
|
.Nm sleepq_timedwait_sig ,
|
|
.Nm sleepq_wait ,
|
|
.Nm sleepq_wait_sig
|
|
.Nd manage the queues of sleeping threads
|
|
.Sh SYNOPSIS
|
|
.In sys/param.h
|
|
.In sys/sleepqueue.h
|
|
.Ft void
|
|
.Fn init_sleepqueues "void"
|
|
.Ft void
|
|
.Fn sleepq_abort "struct thread *td"
|
|
.Ft void
|
|
.Fn sleepq_add "struct sleepqueue *sq" "void *wchan" "struct mtx *lock" "const char *wmesg" "int flags"
|
|
.Ft struct sleepqueue *
|
|
.Fn sleepq_alloc "void"
|
|
.Ft void
|
|
.Fn sleepq_broadcast "void *wchan" "int flags" "int pri"
|
|
.Ft int
|
|
.Fn sleepq_calc_signal_retval "int sig"
|
|
.Ft int
|
|
.Fn sleepq_catch_signals "void *wchan"
|
|
.Ft void
|
|
.Fn sleepq_free "struct sleepqueue *sq"
|
|
.Ft struct sleepqueue *
|
|
.Fn sleepq_lookup "void *wchan"
|
|
.Ft void
|
|
.Fn sleepq_release "void *wchan"
|
|
.Ft void
|
|
.Fn sleepq_remove "struct thread *td" "void *wchan"
|
|
.Ft void
|
|
.Fn sleepq_signal "void *wchan" "int flags" "int pri"
|
|
.Ft void
|
|
.Fn sleepq_set_timeout "void *wchan" "int timo"
|
|
.Ft int
|
|
.Fn sleepq_timedwait "void *wchan" "int signal_caught"
|
|
.Ft int
|
|
.Fn sleepq_timedwait_sig "void *wchan" "int signal_caught"
|
|
.Ft void
|
|
.Fn sleepq_wait "void *wchan"
|
|
.Ft int
|
|
.Fn sleepq_wait_sig "void *wchan"
|
|
.Sh DESCRIPTION
|
|
Sleep queues provide a mechanism for suspending execution of a thread until
|
|
some condition is met.
|
|
Each queue is associated with a specific wait channel when it is active,
|
|
and only one queue may be associated with a wait channel at any given point
|
|
in time.
|
|
An active queue holds a list of threads that are blocked on the associated
|
|
wait channel.
|
|
Threads that are not blocked on a wait channel have an associated inactive
|
|
sleep queue.
|
|
When a thread blocks on a wait channel it donates its inactive sleep queue
|
|
to the wait channel.
|
|
When a thread is resumed,
|
|
the wait channel that it was blocked on gives it an inactive sleep queue for
|
|
later use.
|
|
The
|
|
.Fn sleepq_alloc
|
|
allocates an inactive sleep queue and is used to assign a sleep queue to a
|
|
thread during thread creation.
|
|
The
|
|
.Fn sleepq_free
|
|
function frees the resources associated with an inactive sleep queue and is
|
|
used to free a queue during thread destruction.
|
|
.Pp
|
|
Active sleep queues are stored in a hash table hashed on the addresses pointed
|
|
to by wait channels.
|
|
Each bucket in the hash table contains a sleep queue chain.
|
|
A sleep queue chain contains a spin mutex and a list of sleep queues that hash
|
|
to that specific chain.
|
|
Active sleep queues are protected by their chain's spin mutex.
|
|
The
|
|
.Fn init_sleepqueues
|
|
function initializes the hash table of sleep queue chains.
|
|
.Pp
|
|
The
|
|
.Fn sleepq_lookup
|
|
function locks the sleep queue chain associated with
|
|
.Fa wchan
|
|
and returns a pointer to the current active sleep queue for that wait channel
|
|
or
|
|
.Dv NULL
|
|
if there currently is not an active sleep queue.
|
|
The
|
|
.Fn sleepq_release
|
|
function unlocks the sleep queue chain associated with
|
|
.Fn wchan
|
|
and is primarily useful when aborting a pending sleep request before one of
|
|
the wait functions is called.
|
|
.Pp
|
|
The
|
|
.Fn sleepq_add
|
|
function places the current thread on the sleep queue associated with the
|
|
wait channel
|
|
.Fa wchan .
|
|
The associated sleep queue chain must be locked by a call to
|
|
.Fn sleepq_lookup
|
|
when this function is called and its return value should be passed as the
|
|
.Fa sq
|
|
parameter.
|
|
If a mutex is specified via the
|
|
.Fa lock
|
|
argument, then the sleep queue code will perform extra checks to ensure that
|
|
the mutex is held for all threads sleeping on
|
|
.Fa wchan .
|
|
The
|
|
.Fa wmesg
|
|
parameter should be a short description of
|
|
.Fa wchan .
|
|
The
|
|
.Fa flags
|
|
parameter currently only specifies the type of sleep queue being slept on.
|
|
A value of
|
|
0
|
|
indicates a sleep queue used by
|
|
.Xr msleep 9
|
|
and a value of
|
|
.Dv SLEEPQ_CONDVAR
|
|
indicates a sleep queue used by
|
|
.Xr condvar 9 .
|
|
A timeout on the sleep may be specified by calling
|
|
.Fn sleepq_set_timeout
|
|
after
|
|
.Fn sleepq_add .
|
|
The
|
|
.Fa wchan
|
|
parameter should be the same value from the preceding call to
|
|
.Fn sleepq_add .
|
|
The
|
|
.Fa timo
|
|
parameter should specify the timeout value in ticks.
|
|
The thread may be marked interruptible by calling
|
|
.Fn sleepq_catch_signals
|
|
with
|
|
.Fa wchan
|
|
set to the wait channel.
|
|
The function returns a signal number if there are any pending signals for
|
|
the current thread and 0 if there is not a pending signal.
|
|
.Pp
|
|
Once the thread is ready to suspend,
|
|
one of the wait functions is called to put the thread to sleep until it is
|
|
awakened and context switch to another thread.
|
|
The
|
|
.Fn sleepq_wait
|
|
function is used for non-interruptible sleeps that do not have a timeout.
|
|
The
|
|
.Fn sleepq_timedwait
|
|
function is used for non-interruptible sleeps that have had a timeout set via
|
|
.Fn sleepq_set_timeout .
|
|
The
|
|
.Fn sleepq_wait_sig
|
|
function is used for interruptible sleeps that do not have a timeout.
|
|
The
|
|
.Fn sleepq_timedwait_sig
|
|
function is used for interruptible sleeps that do have a timeout set.
|
|
The
|
|
.Fa wchan
|
|
argument to all of the wait functions is the wait channel being slept on.
|
|
The
|
|
.Fa signal_caught
|
|
parameter to the timed wait functions specifies if a previous call to
|
|
.Fn sleepq_catch_signals
|
|
found a pending signal.
|
|
.Pp
|
|
When the thread is resumed,
|
|
the wait functions return a non-zero value if the thread was awakened due to
|
|
an interrupt other than a signal or a timeout.
|
|
If the sleep timed out, then
|
|
.Er EWOULDBLOCK
|
|
is returned.
|
|
If the sleep was interrupted by something other than a signal,
|
|
then some other return value will be returned.
|
|
If zero is returned after resuming from an interruptible sleep,
|
|
then
|
|
.Fn sleepq_calc_signal_retval
|
|
should be called to determine if the sleep was interrupted by a signal.
|
|
If so,
|
|
.Fn sleepq_calc_signal_retval
|
|
returns
|
|
.Er ERESTART
|
|
if the interrupting signal is restartable and
|
|
.Er EINTR
|
|
otherwise.
|
|
If the sleep was not interrupted by a signal,
|
|
.Fn sleepq_calc_signal_retval
|
|
will return 0.
|
|
.Pp
|
|
A sleeping thread is normally resumed by the
|
|
.Fn sleepq_broadcast
|
|
and
|
|
.Fn sleepq_signal
|
|
functions.
|
|
The
|
|
.Fn sleepq_signal
|
|
function awakens the highest priority thread sleeping on a wait channel while
|
|
.Fn sleepq_broadcast
|
|
awakens all of the threads sleeping on a wait channel.
|
|
The
|
|
.Fa wchan
|
|
argument specifics which wait channel to awaken.
|
|
The
|
|
.Fa flags
|
|
argument should match the
|
|
.Fa flags
|
|
argument passed to
|
|
.Fn sleepq_add
|
|
by the threads sleeping on the wait channel.
|
|
If the
|
|
.Fa pri
|
|
argument does not equal \-1,
|
|
then each thread that is awakened will have its priority raised to
|
|
.Fa pri
|
|
if it has a lower priority.
|
|
.Pp
|
|
A thread in an interruptible sleep can be interrupted by another thread via
|
|
the
|
|
.Fn sleepq_abort
|
|
function.
|
|
The
|
|
.Fa td
|
|
argument specifies the thread to interrupt.
|
|
An individual thread can also be awakened from sleeping on a specific wait
|
|
channel via the
|
|
.Fn sleepq_remove
|
|
function.
|
|
The
|
|
.Fa td
|
|
argument specifies the thread to awaken and the
|
|
.Fa wchan
|
|
argument specifies the wait channel to awaken it from.
|
|
If the thread
|
|
.Fa td
|
|
is not blocked on the the wait channel
|
|
.Fa wchan
|
|
then this function will not do anything,
|
|
even if the thread is asleep on a different wait channel.
|
|
This function should only be used if one of the other functions above is not
|
|
sufficient.
|
|
One possible use is waking up a specific thread from a widely shared sleep
|
|
channel.
|
|
.Pp
|
|
The sleep queue interface is currently used to implement the
|
|
.Xr msleep 9
|
|
and
|
|
.Xr condvar 9
|
|
interfaces.
|
|
Almost all other code in the kernel should use one of those interfaces rather
|
|
than manipulating sleep queues directly.
|
|
.Sh SEE ALSO
|
|
.Xr condvar 9 ,
|
|
.Xr msleep 9 ,
|
|
.Xr runqueue 9 ,
|
|
.Xr scheduler 9
|