NAME
init_sleepqueues,
sleepq_abort, sleepq_add,
sleepq_alloc,
sleepq_broadcast,
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);
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
pri);
int
sleepq_timedwait_sig(void
*wchan, int
pri);
int
sleepq_type(void
*wchan);
void
sleepq_wait(void
*wchan, int
pri);
int
sleepq_wait_sig(void
*wchan, int
pri);
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.
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 pri
argument is used to set the priority of the thread when it is awakened. If
it is set to zero, the thread's priority is left alone.
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.
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.