1 .\" Copyright (c) 2000-2004 John H. Baldwin <jhb@FreeBSD.org>
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26 .Dd September 22, 2014
30 .Nm init_sleepqueues ,
34 .Nm sleepq_broadcast ,
41 .Nm sleepq_set_timeout ,
42 .Nm sleepq_set_timeout_sbt ,
44 .Nm sleepq_timedwait ,
45 .Nm sleepq_timedwait_sig ,
49 .Nd manage the queues of sleeping threads
54 .Fn init_sleepqueues "void"
56 .Fn sleepq_abort "struct thread *td"
58 .Fn sleepq_add "void *wchan" "struct lock_object *lock" "const char *wmesg" "int flags" "int queue"
59 .Ft struct sleepqueue *
60 .Fn sleepq_alloc "void"
62 .Fn sleepq_broadcast "void *wchan" "int flags" "int pri" "int queue"
64 .Fn sleepq_free "struct sleepqueue *sq"
65 .Ft struct sleepqueue *
66 .Fn sleepq_lookup "void *wchan"
68 .Fn sleepq_lock "void *wchan"
70 .Fn sleepq_release "void *wchan"
72 .Fn sleepq_remove "struct thread *td" "void *wchan"
74 .Fn sleepq_signal "void *wchan" "int flags" "int pri" "int queue"
76 .Fn sleepq_set_timeout "void *wchan" "int timo"
78 .Fn sleepq_set_timeout_sbt "void *wchan" "sbintime_t sbt" \
79 "sbintime_t pr" "int flags"
81 .Fn sleepq_sleepcnt "void *wchan" "int queue"
83 .Fn sleepq_timedwait "void *wchan" "int pri"
85 .Fn sleepq_timedwait_sig "void *wchan" "int pri"
87 .Fn sleepq_type "void *wchan"
89 .Fn sleepq_wait "void *wchan" "int pri"
91 .Fn sleepq_wait_sig "void *wchan" "int pri"
93 Sleep queues provide a mechanism for suspending execution of a thread until
94 some condition is met.
95 Each queue is associated with a specific wait channel when it is active,
96 and only one queue may be associated with a wait channel at any given point
98 The implementation of each wait channel splits its sleepqueue into 2 sub-queues
99 in order to enable some optimizations on threads' wakeups.
100 An active queue holds a list of threads that are blocked on the associated
102 Threads that are not blocked on a wait channel have an associated inactive
104 When a thread blocks on a wait channel it donates its inactive sleep queue
106 When a thread is resumed,
107 the wait channel that it was blocked on gives it an inactive sleep queue for
112 function allocates an inactive sleep queue and is used to assign a
113 sleep queue to a thread during thread creation.
116 function frees the resources associated with an inactive sleep queue and is
117 used to free a queue during thread destruction.
119 Active sleep queues are stored in a hash table hashed on the addresses pointed
121 Each bucket in the hash table contains a sleep queue chain.
122 A sleep queue chain contains a spin mutex and a list of sleep queues that hash
123 to that specific chain.
124 Active sleep queues are protected by their chain's spin mutex.
127 function initializes the hash table of sleep queue chains.
131 function locks the sleep queue chain associated with wait channel
136 returns a pointer to the currently active sleep queue for that wait
137 channel associated with
141 if there is no active sleep queue associated with
144 It requires the sleep queue chain associated with
146 to have been locked by a prior call to
151 function unlocks the sleep queue chain associated with
153 and is primarily useful when aborting a pending sleep request before one of
154 the wait functions is called.
158 function places the current thread on the sleep queue associated with the
161 The sleep queue chain associated with argument
163 must be locked by a prior call to
165 when this function is called.
166 If a lock is specified via the
168 argument, and if the kernel was compiled with
169 .Cd "options INVARIANTS" ,
170 then the sleep queue code will perform extra checks to ensure that
171 the lock is used by all threads sleeping on
175 parameter should be a short description of
179 parameter is a bitmask consisting of the type of sleep queue being slept on
180 and zero or more optional flags.
183 parameter specifies the sub-queue, in which the contending thread will be
186 There are currently three types of sleep queues:
188 .Bl -tag -width ".Dv SLEEPQ_CONDVAR" -compact
189 .It Dv SLEEPQ_CONDVAR
190 A sleep queue used to implement condition variables.
192 A sleep queue used to implement
198 A sleep queue used to implement
202 There are currently two optional flag:
204 .Bl -tag -width ".Dv SLEEPQ_INTERRUPTIBLE" -compact
205 .It Dv SLEEPQ_INTERRUPTIBLE
206 The current thread is entering an interruptible sleep.
208 .Bl -tag -width ".Dv SLEEPQ_STOP_ON_BDRY" -compact
209 .It Dv SLEEPQ_STOP_ON_BDRY
210 When thread is entering an interruptible sleep, do not stop it upon
211 arrival of stop action, like
216 A timeout on the sleep may be specified by calling
217 .Fn sleepq_set_timeout
222 parameter should be the same value from the preceding call to
224 and the sleep queue chain associated with
226 must have been locked by a prior call to
230 parameter should specify the timeout value in ticks.
232 .Fn sleepq_set_timeout_sbt
237 It allows to specify relative or absolute wakeup time with higher resolution
242 allows to specify wanted absolute event precision.
245 allows to pass additional
246 .Fn callout_reset_sbt
249 Once the thread is ready to suspend,
250 one of the wait functions is called to put the current thread to sleep
251 until it is awakened and to context switch to another thread.
254 function is used for non-interruptible sleeps that do not have a timeout.
257 function is used for non-interruptible sleeps that have had a timeout set via
258 .Fn sleepq_set_timeout .
261 function is used for interruptible sleeps that do not have a timeout.
263 .Fn sleepq_timedwait_sig
264 function is used for interruptible sleeps that do have a timeout set.
267 argument to all of the wait functions is the wait channel being slept
269 The sleep queue chain associated with argument
271 needs to have been locked with a prior call to
275 argument is used to set the priority of the thread when it is awakened.
276 If it is set to zero, the thread's priority is left alone.
278 When the thread is resumed,
279 the wait functions return a non-zero value if the thread was awakened due to
280 an interrupt other than a signal or a timeout.
281 If the sleep timed out, then
284 If the sleep was interrupted by something other than a signal,
285 then some other return value will be returned.
287 A sleeping thread is normally resumed by the
294 function awakens the highest priority thread sleeping on a wait channel while
296 awakens all of the threads sleeping on a wait channel.
299 argument specifics which wait channel to awaken.
302 argument must match the sleep queue type contained in the
306 by the threads sleeping on the wait channel.
309 argument does not equal \-1,
310 then each thread that is awakened will have its priority raised to
312 if it has a lower priority.
313 The sleep queue chain associated with argument
315 must be locked by a prior call to
317 before calling any of these functions.
320 argument specifies the sub-queue, from which threads need to be woken up.
322 A thread in an interruptible sleep can be interrupted by another thread via
328 argument specifies the thread to interrupt.
329 An individual thread can also be awakened from sleeping on a specific wait
335 argument specifies the thread to awaken and the
337 argument specifies the wait channel to awaken it from.
340 is not blocked on the wait channel
342 then this function will not do anything,
343 even if the thread is asleep on a different wait channel.
344 This function should only be used if one of the other functions above is not
346 One possible use is waking up a specific thread from a widely shared sleep
351 function offer a simple way to retrieve the number of threads sleeping for
359 function returns the type of
361 associated to a sleepqueue.
365 .Fn sleepq_broadcast ,
368 functions all return a boolean value.
369 If the return value is true,
370 then at least one thread was resumed that is currently swapped out.
371 The caller is responsible for awakening the scheduler process so that the
372 resumed thread will be swapped back in.
373 This is done by calling the
375 function after releasing the sleep queue chain lock via a call to
378 The sleep queue interface is currently used to implement the
383 Almost all other code in the kernel should use one of those interfaces rather
384 than manipulating sleep queues directly.