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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 */
58 .Ft struct taskqueue *
59 .Fn taskqueue_create "const char *name" "int mflags" "taskqueue_enqueue_fn enqueue" "void *context"
60 .Ft struct taskqueue *
61 .Fn taskqueue_create_fast "const char *name" "int mflags" "taskqueue_enqueue_fn enqueue" "void *context"
63 .Fn taskqueue_free "struct taskqueue *queue"
65 .Fn taskqueue_enqueue "struct taskqueue *queue" "struct task *task"
67 .Fn taskqueue_enqueue_fast "struct taskqueue *queue" "struct task *task"
69 .Fn taskqueue_enqueue_timeout "struct taskqueue *queue" "struct timeout_task *timeout_task" "int ticks"
71 .Fn taskqueue_cancel "struct taskqueue *queue" "struct task *task" "u_int *pendp"
73 .Fn taskqueue_cancel_timeout "struct taskqueue *queue" "struct timeout_task *timeout_task" "u_int *pendp"
75 .Fn taskqueue_drain "struct taskqueue *queue" "struct task *task"
77 .Fn taskqueue_drain_timeout "struct taskqueue *queue" "struct timeout_task *timeout_task"
79 .Fn taskqueue_member "struct taskqueue *queue" "struct thread *td"
81 .Fn taskqueue_run "struct taskqueue *queue"
82 .Fn TASK_INIT "struct task *task" "int priority" "task_fn_t func" "void *context"
83 .Fn TASK_INITIALIZER "int priority" "task_fn_t func" "void *context"
84 .Fn TASKQUEUE_DECLARE "name"
85 .Fn TASKQUEUE_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init"
86 .Fn TASKQUEUE_FAST_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init"
87 .Fn TASKQUEUE_DEFINE_THREAD "name"
88 .Fn TASKQUEUE_FAST_DEFINE_THREAD "name"
89 .Fn TIMEOUT_TASK_INIT "struct taskqueue *queue" "struct timeout_task *timeout_task" "int priority" "task_fn_t func" "void *context"
91 These functions provide a simple interface for asynchronous execution
96 is used to create new queues.
99 include a name that should be unique,
102 flags that specify whether the call to
105 a function that is called from
106 .Fn taskqueue_enqueue
107 when a task is added to the queue,
108 and a pointer to the memory location where the identity of the
109 thread that services the queue is recorded.
110 .\" XXX The rest of the sentence gets lots in relation to the first part.
111 The function called from
112 .Fn taskqueue_enqueue
113 must arrange for the queue to be processed
114 (for instance by scheduling a software interrupt or waking a kernel
116 The memory location where the thread identity is recorded is used
117 to signal the service thread(s) to terminate--when this value is set to
118 zero and the thread is signaled it will terminate.
119 If the queue is intended for use in fast interrupt handlers
120 .Fn taskqueue_create_fast
121 should be used in place of
122 .Fn taskqueue_create .
126 should be used to free the memory used by the queue.
127 Any tasks that are on the queue will be executed at this time after
128 which the thread servicing the queue will be signaled that it should exit.
130 To add a task to the list of tasks queued on a taskqueue, call
131 .Fn taskqueue_enqueue
132 with pointers to the queue and task.
136 then it is simply incremented to reflect the number of times the task
137 was enqueued, up to a cap of USHRT_MAX.
139 the task is added to the list before the first task which has a lower
141 value or at the end of the list if no tasks have a lower priority.
142 Enqueueing a task does not perform any memory allocation which makes
143 it suitable for calling from an interrupt handler.
144 This function will return
146 if the queue is being freed.
149 .Fn taskqueue_enqueue_fast
150 should be used in place of
151 .Fn taskqueue_enqueue
152 when the enqueuing must happen from a fast interrupt handler.
153 This method uses spin locks to avoid the possibility of sleeping in the fast
156 When a task is executed,
157 first it is removed from the queue,
160 is recorded and then the field is zeroed.
163 from the task structure is called with the value of the field
165 as its first argument
168 as its second argument.
173 is called on the task pointer passed to
174 .Fn taskqueue_enqueue .
177 .Fn taskqueue_enqueue_timeout
178 is used to schedule the enqueue after the specified amount of
180 Only non-fast task queues can be used for
186 function is used to cancel a task.
189 count is cleared, and the old value returned in the reference
194 If the task is currently running,
196 is returned, otherwise 0.
197 To implement a blocking
199 that waits for a running task to finish, it could look like:
200 .Bd -literal -offset indent
201 while (taskqueue_cancel(tq, task, NULL) != 0)
202 taskqueue_drain(tq, task);
206 .Fn taskqueue_drain ,
207 the caller is responsible for ensuring that the task is not re-enqueued
208 after being canceled.
211 .Fn taskqueue_cancel_timeout
212 function is used to cancel the scheduled task execution.
216 function is used to wait for the task to finish, and
218 .Fn taskqueue_drain_timeout
219 function is used to wait for the scheduled task to finish.
220 There is no guarantee that the task will not be
221 enqueued after call to
222 .Fn taskqueue_drain .
230 is part of the given taskqueue
238 function will run all pending tasks in the specified
240 Normally this function is only used internally.
243 .Fn TASK_INIT "task" "priority" "func" "context"
244 is provided to initialise a
249 macro generates an initializer for a task structure.
251 .Fn TIMEOUT_TASK_INIT "queue" "timeout_task" "priority" "func" "context"
260 are simply copied into the task structure fields and the
265 .Fn TASKQUEUE_DECLARE "name" ,
266 .Fn TASKQUEUE_DEFINE "name" "enqueue" "context" "init" ,
267 .Fn TASKQUEUE_FAST_DEFINE "name" "enqueue" "context" "init" ,
269 .Fn TASKQUEUE_DEFINE_THREAD "name"
270 .Fn TASKQUEUE_FAST_DEFINE_THREAD "name"
271 are used to declare a reference to a global queue, to define the
272 implementation of the queue, and declare a queue that uses its own thread.
275 macro arranges to call
277 with the values of its
282 arguments during system initialisation.
284 .Fn taskqueue_create ,
287 argument to the macro is executed as a C statement,
288 allowing any further initialisation to be performed
289 (such as registering an interrupt handler etc.)
292 .Fn TASKQUEUE_DEFINE_THREAD
293 macro defines a new taskqueue with its own kernel thread to serve tasks.
295 .Vt struct taskqueue *taskqueue_name
296 is used to enqueue tasks onto the queue.
298 .Fn TASKQUEUE_FAST_DEFINE
300 .Fn TASKQUEUE_FAST_DEFINE_THREAD
304 .Fn TASKQUEUE_DEFINE_THREAD
305 respectively but taskqueue is created with
306 .Fn taskqueue_create_fast .
307 .Ss Predefined Task Queues
308 The system provides four global taskqueues,
311 .Va taskqueue_swi_giant ,
313 .Va taskqueue_thread .
316 queue is for swi handlers dispatched from fast interrupt handlers,
317 where sleep mutexes cannot be used.
318 The swi taskqueues are run via a software interrupt mechanism.
321 queue runs without the protection of the
324 .Va taskqueue_swi_giant
325 queue runs with the protection of the
330 runs in a kernel thread context, and tasks run from this thread do
334 If the caller wants to run under
336 he should explicitly acquire and release
338 in his taskqueue handler routine.
342 .Fn taskqueue_enqueue
343 with the value of the global taskqueue variable for the queue you wish to
345 .Va ( taskqueue_swi ,
346 .Va taskqueue_swi_giant ,
348 .Va taskqueue_thread ) .
350 .Fn taskqueue_enqueue_fast
351 for the global taskqueue variable
354 The software interrupt queues can be used,
355 for instance, for implementing interrupt handlers which must perform a
356 significant amount of processing in the handler.
357 The hardware interrupt handler would perform minimal processing of the
358 interrupt and then enqueue a task to finish the work.
359 This reduces to a minimum
360 the amount of time spent with interrupts disabled.
362 The thread queue can be used, for instance, by interrupt level routines
363 that need to call kernel functions that do things that can only be done
364 from a thread context.
365 (e.g., call malloc with the M_WAITOK flag.)
367 Note that tasks queued on shared taskqueues such as
369 may be delayed an indeterminate amount of time before execution.
370 If queueing delays cannot be tolerated then a private taskqueue should
371 be created with a dedicated processing thread.
377 This interface first appeared in
379 There is a similar facility called work_queue in the Linux kernel.
381 This manual page was written by