table of contents
SLEEPQUEUE(9) | Kernel Developer's Manual | SLEEPQUEUE(9) |
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_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); 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); 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 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. 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 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)January 25, 2010 | Debian |