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36 .Nd asynchronous task execution
44 typedef void (*task_fn_t)(void *context, int pending);
46 typedef void (*taskqueue_enqueue_fn)(void *context);
49 STAILQ_ENTRY(task) ta_link; /* link for queue */
50 u_short ta_pending; /* count times queued */
51 u_short ta_priority; /* priority of task in queue */
52 task_fn_t ta_func; /* task handler */
53 void *ta_context; /* argument for handler */
56 .Ft struct taskqueue *
57 .Fn taskqueue_create "const char *name" "int mflags" "taskqueue_enqueue_fn enqueue" "void *context" "struct proc **"
59 .Fn taskqueue_free "struct taskqueue *queue"
60 .Ft struct taskqueue *
61 .Fn taskqueue_find "const char *name"
63 .Fn taskqueue_enqueue "struct taskqueue *queue" "struct task *task"
65 .Fn taskqueue_enqueue_fast "struct taskqueue *queue" "struct task *task"
67 .Fn taskqueue_run "struct taskqueue *queue"
69 .Fn taskqueue_run_fast "struct taskqueue *queue"
71 .Fn taskqueue_drain "struct taskqueue *queue" "struct task *task"
72 .Fn TASK_INIT "struct task *task" "int priority" "task_fn_t *func" "void *context"
73 .Fn TASKQUEUE_DECLARE "name"
74 .Fn TASKQUEUE_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init"
75 .Fn TASKQUEUE_DEFINE_THREAD "name"
77 These functions provide a simple interface for asynchronous execution
82 is used to create new queues.
85 include a name that should be unique,
88 flags that specify whether the call to
91 a function that is called from
93 when a task is added to the queue,
94 and a pointer to the memory location where the identity of the
95 thread that services the queue is recorded.
96 .\" XXX The rest of the sentence gets lots in relation to the first part.
97 The function called from
99 must arrange for the queue to be processed
100 (for instance by scheduling a software interrupt or waking a kernel
102 The memory location where the thread identity is recorded is used
103 to signal the service thread(s) to terminate--when this value is set to
104 zero and the thread is signaled it will terminate.
108 should be used to remove the queue from the global list of queues
109 and free the memory used by the queue.
110 Any tasks that are on the queue will be executed at this time after
111 which the thread servicing the queue will be signaled that it should exit.
113 The system maintains a list of all queues which can be searched using
115 The first queue whose name matches is returned, otherwise
118 To add a task to the list of tasks queued on a taskqueue, call
119 .Fn taskqueue_enqueue
120 with pointers to the queue and task.
124 then it is simply incremented to reflect the number of times the task
127 the task is added to the list before the first task which has a lower
129 value or at the end of the list if no tasks have a lower priority.
130 Enqueueing a task does not perform any memory allocation which makes
131 it suitable for calling from an interrupt handler.
132 This function will return
134 if the queue is being freed.
137 .Fn taskqueue_enqueue_fast
138 should be used in place of
139 .Fn taskqueue_enqueue
140 when the enqueuing must happen from a fast interrupt handler.
141 This method uses spin locks to avoid the possibility of sleeping in the fast
144 To execute all the tasks on a queue,
148 .Fn taskqueue_run_fast
149 depending on the flavour of the queue.
150 When a task is executed,
151 first it is removed from the queue,
154 is recorded and then the field is zeroed.
157 from the task structure is called with the value of the field
159 as its first argument
162 as its second argument.
167 is called on the task pointer passed to
168 .Fn taskqueue_enqueue .
172 function is used to wait for the task to finish.
173 There is no guarantee that the task will not be
174 enqueued after call to
175 .Fn taskqueue_drain .
178 .Fn TASK_INIT "task" "priority" "func" "context"
179 is provided to initialise a
187 are simply copied into the task structure fields and the
192 .Fn TASKQUEUE_DECLARE "name" ,
193 .Fn TASKQUEUE_DEFINE "name" "enqueue" "context" "init" ,
195 .Fn TASKQUEUE_DEFINE_THREAD "name"
196 are used to declare a reference to a global queue, to define the
197 implementation of the queue, and declare a queue that uses its own thread.
200 macro arranges to call
202 with the values of its
207 arguments during system initialisation.
209 .Fn taskqueue_create ,
212 argument to the macro is executed as a C statement,
213 allowing any further initialisation to be performed
214 (such as registering an interrupt handler etc.)
217 .Fn TASKQUEUE_DEFINE_THREAD
218 macro defines a new taskqueue with its own kernel thread to serve tasks.
220 .Vt struct proc *taskqueue_name_proc
221 is defined which contains the kernel thread serving the tasks.
223 .Vt struct taskqueue *taskqueue_name
224 is used to enqueue tasks onto the queue.
225 .Ss Predefined Task Queues
226 The system provides four global taskqueues,
229 .Va taskqueue_swi_giant ,
231 .Va taskqueue_thread .
234 queue is for swi handlers dispatched from fast interrupt handlers,
235 where sleep mutexes cannot be used.
236 The swi taskqueues are run via a software interrupt mechanism.
239 queue runs without the protection of the
242 .Va taskqueue_swi_giant
243 queue runs with the protection of the
248 runs in a kernel thread context, and tasks run from this thread do
252 If the caller wants to run under
254 he should explicitly acquire and release
256 in his taskqueue handler routine.
260 .Fn taskqueue_enqueue
261 with the value of the global taskqueue variable for the queue you wish to
263 .Va ( taskqueue_swi ,
264 .Va taskqueue_swi_giant ,
266 .Va taskqueue_thread ) .
268 .Fn taskqueue_enqueue_fast
269 for the global taskqueue variable
272 The software interrupt queues can be used,
273 for instance, for implementing interrupt handlers which must perform a
274 significant amount of processing in the handler.
275 The hardware interrupt handler would perform minimal processing of the
276 interrupt and then enqueue a task to finish the work.
277 This reduces to a minimum
278 the amount of time spent with interrupts disabled.
280 The thread queue can be used, for instance, by interrupt level routines
281 that need to call kernel functions that do things that can only be done
282 from a thread context.
283 (e.g., call malloc with the M_WAITOK flag.)
285 Note that tasks queued on shared taskqueues such as
287 may be delayed an indeterminate amount of time before execution.
288 If queueing delays cannot be tolerated then a private taskqueue should
289 be created with a dedicated processing thread.
295 This interface first appeared in
297 There is a similar facility called tqueue in the Linux kernel.
299 This manual page was written by
303 .Fn taskqueue_create_fast .