NAME¶
init_sleepqueues
,
sleepq_abort
,
sleepq_add
,
sleepq_alloc
,
sleepq_broadcast
,
sleepq_calc_signal_retval
,
sleepq_catch_signals
,
sleepq_free
,
sleepq_lock
,
sleepq_lookup
,
sleepq_release
,
sleepq_remove
,
sleepq_signal
,
sleepq_set_timeout
,
sleepq_set_timeout_sbt
,
sleepq_sleepcnt
,
sleepq_timedwait
,
sleepq_timedwait_sig
,
sleepq_type
,
sleepq_wait
,
sleepq_wait_sig
—
manage the queues of sleeping threads
SYNOPSIS¶
#include
<sys/param.h>
#include
<sys/sleepqueue.h>
void
init_sleepqueues
(
void);
int
sleepq_abort
(
struct
thread *td);
void
sleepq_add
(
void
*wchan,
struct
lock_object *lock,
const char
*wmesg,
int
flags,
int
queue);
struct sleepqueue *
sleepq_alloc
(
void);
int
sleepq_broadcast
(
void
*wchan,
int
flags,
int
pri,
int
queue);
int
sleepq_calc_signal_retval
(
int
sig);
int
sleepq_catch_signals
(
void
*wchan);
void
sleepq_free
(
struct
sleepqueue *sq);
struct sleepqueue *
sleepq_lookup
(
void
*wchan);
void
sleepq_lock
(
void
*wchan);
void
sleepq_release
(
void
*wchan);
void
sleepq_remove
(
struct
thread *td,
void
*wchan);
int
sleepq_signal
(
void
*wchan,
int
flags,
int
pri,
int
queue);
void
sleepq_set_timeout
(
void
*wchan,
int
timo);
void
sleepq_set_timeout_sbt
(
void
*wchan,
sbintime_t sbt,
sbintime_t pr,
int flags);
u_int
sleepq_sleepcnt
(
void
*wchan,
int
queue);
int
sleepq_timedwait
(
void
*wchan);
int
sleepq_timedwait_sig
(
void
*wchan,
int
signal_caught);
int
sleepq_type
(
void
*wchan);
void
sleepq_wait
(
void
*wchan);
int
sleepq_wait_sig
(
void
*wchan);
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. The implementation of each wait channel splits its
sleepqueue into 2 sub-queues in order to enable some optimizations on threads'
wakeups. 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
sleepq_alloc
() function allocates an
inactive sleep queue and is used to assign a sleep queue to a thread during
thread creation. The
sleepq_free
() function
frees the resources associated with an inactive sleep queue and is used to
free a queue during thread destruction.
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
init_sleepqueues
()
function initializes the hash table of sleep queue chains.
The
sleepq_lock
() function locks the sleep
queue chain associated with wait channel
wchan.
The
sleepq_lookup
() returns a pointer to the
currently active sleep queue for that wait channel associated with
wchan or
NULL
if there is no active sleep queue
associated with argument
wchan. It requires
the sleep queue chain associated with
wchan
to have been locked by a prior call to
sleepq_lock
().
The
sleepq_release
() function unlocks the
sleep queue chain associated with
wchan
()
and is primarily useful when aborting a pending sleep request before one of
the wait functions is called.
The
sleepq_add
() function places the current
thread on the sleep queue associated with the wait channel
wchan. The sleep queue chain associated with
argument
wchan must be locked by a prior call
to
sleepq_lock
() when this function is
called. If a lock is specified via the
lock
argument, and if the kernel was compiled with
options INVARIANTS
, then the sleep queue
code will perform extra checks to ensure that the lock is used by all threads
sleeping on
wchan. The
wmesg parameter should be a short description
of
wchan. The
flags parameter is a bitmask consisting of
the type of sleep queue being slept on and zero or more optional flags. The
queue parameter specifies the sub-queue, in
which the contending thread will be inserted.
There are currently three types of sleep queues:
SLEEPQ_CONDVAR
- A sleep queue used to implement condition variables.
SLEEPQ_SLEEP
- A sleep queue used to implement sleep(9),
wakeup(9) and
wakeup_one(9).
SLEEPQ_PAUSE
- A sleep queue used to implement
pause(9).
There are currently two optional flag:
SLEEPQ_INTERRUPTIBLE
- The current thread is entering an interruptible sleep.
SLEEPQ_STOP_ON_BDRY
- When thread is entering an interruptible sleep, do not stop it upon
arrival of stop action, like
SIGSTOP
.
Wake it up instead.
A timeout on the sleep may be specified by calling
sleepq_set_timeout
() after
sleepq_add
(). The
wchan parameter should be the same value from
the preceding call to
sleepq_add
(), and the
sleep queue chain associated with
wchan must
have been locked by a prior call to
sleepq_lock
(). The
timo parameter should specify the timeout
value in ticks.
sleepq_set_timeout_sbt
() function takes
sbt argument instead of
timo. It allows to specify relative or
absolute wakeup time with higher resolution in form of
sbintime_t. The parameter
pr allows to specify wanted absolute event
precision. The parameter
flags allows to pass
additional
callout_reset_sbt
() flags.
The current thread may be marked interruptible by calling
sleepq_catch_signals
() with
wchan set to the wait channel. This function
returns a signal number if there are any pending signals for the current
thread and 0 if there is not a pending signal. The sleep queue chain
associated with argument
wchan should have
been locked by a prior call to
sleepq_lock
().
Once the thread is ready to suspend, one of the wait functions is called to put
the current thread to sleep until it is awakened and to context switch to
another thread. The
sleepq_wait
() function
is used for non-interruptible sleeps that do not have a timeout. The
sleepq_timedwait
() function is used for
non-interruptible sleeps that have had a timeout set via
sleepq_set_timeout
(). The
sleepq_wait_sig
() function is used for
interruptible sleeps that do not have a timeout. The
sleepq_timedwait_sig
() function is used for
interruptible sleeps that do have a timeout set. The
wchan argument to all of the wait functions
is the wait channel being slept on. The sleep queue chain associated with
argument
wchan needs to have been locked with
a prior call to
sleepq_lock
(). The
signal_caught parameter to
sleepq_timedwait_sig
() specifies if a
previous call to
sleepq_catch_signals
()
found a pending signal.
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
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
sleepq_calc_signal_retval
() should be
called to determine if the sleep was interrupted by a signal. If so,
sleepq_calc_signal_retval
() returns
ERESTART
if the interrupting signal is
restartable and
EINTR
otherwise. If the
sleep was not interrupted by a signal,
sleepq_calc_signal_retval
() will return 0.
A sleeping thread is normally resumed by the
sleepq_broadcast
() and
sleepq_signal
() functions. The
sleepq_signal
() function awakens the
highest priority thread sleeping on a wait channel while
sleepq_broadcast
() awakens all of the
threads sleeping on a wait channel. The
wchan
argument specifics which wait channel to awaken. The
flags argument must match the sleep queue
type contained in the
flags argument passed
to
sleepq_add
() by the threads sleeping on
the wait channel. If the
pri argument does
not equal -1, then each thread that is awakened will have its priority raised
to
pri if it has a lower priority. The sleep
queue chain associated with argument
wchan
must be locked by a prior call to
sleepq_lock
() before calling any of these
functions. The
queue argument specifies the
sub-queue, from which threads need to be woken up.
A thread in an interruptible sleep can be interrupted by another thread via the
sleepq_abort
() function. The
td argument specifies the thread to
interrupt. An individual thread can also be awakened from sleeping on a
specific wait channel via the
sleepq_remove
() function. The
td argument specifies the thread to awaken
and the
wchan argument specifies the wait
channel to awaken it from. If the thread
td
is not blocked on the wait channel
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.
The
sleepq_sleepcnt
() function offer a simple
way to retrieve the number of threads sleeping for the specified
queue, given a
wchan.
The
sleepq_type
() function returns the type
of
wchan associated to a sleepqueue.
The
sleepq_abort
(),
sleepq_broadcast
(), and
sleepq_signal
() functions all return a
boolean value. If the return value is true, then at least one thread was
resumed that is currently swapped out. The caller is responsible for awakening
the scheduler process so that the resumed thread will be swapped back in. This
is done by calling the
kick_proc0
()
function after releasing the sleep queue chain lock via a call to
sleepq_release
().
The sleep queue interface is currently used to implement the
sleep(9) and
condvar(9) interfaces. Almost all other code in
the kernel should use one of those interfaces rather than manipulating sleep
queues directly.
SEE ALSO¶
condvar(9),
runqueue(9),
scheduler(9),
sleep(9),
timeout(9)