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 threadsSYNOPSIS
#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 orNULL 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).
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.
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 (if SLEEPQ_UNFAIR flag is set,
thread that went to sleep recently) 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)| June 19, 2019 | Debian |