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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"
58 .Ft struct taskqueue *
59 .Fn taskqueue_create_fast "const char *name" "int mflags" "taskqueue_enqueue_fn enqueue" "void *context"
61 .Fn taskqueue_free "struct taskqueue *queue"
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"
73 .Fn taskqueue_member "struct taskqueue *queue" "struct thread *td"
74 .Fn TASK_INIT "struct task *task" "int priority" "task_fn_t *func" "void *context"
75 .Fn TASKQUEUE_DECLARE "name"
76 .Fn TASKQUEUE_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init"
77 .Fn TASKQUEUE_FAST_DEFINE "name" "taskqueue_enqueue_fn enqueue" "void *context" "init"
78 .Fn TASKQUEUE_DEFINE_THREAD "name"
79 .Fn TASKQUEUE_FAST_DEFINE_THREAD "name"
81 These functions provide a simple interface for asynchronous execution
86 is used to create new queues.
89 include a name that should be unique,
92 flags that specify whether the call to
95 a function that is called from
97 when a task is added to the queue,
98 and a pointer to the memory location where the identity of the
99 thread that services the queue is recorded.
100 .\" XXX The rest of the sentence gets lots in relation to the first part.
101 The function called from
102 .Fn taskqueue_enqueue
103 must arrange for the queue to be processed
104 (for instance by scheduling a software interrupt or waking a kernel
106 The memory location where the thread identity is recorded is used
107 to signal the service thread(s) to terminate--when this value is set to
108 zero and the thread is signaled it will terminate.
109 If the queue is intended for use in fast interrupt handlers
110 .Fn taskqueue_create_fast
111 should be used in place of
112 .Fn taskqueue_create .
116 should be used to free the memory used by the queue.
117 Any tasks that are on the queue will be executed at this time after
118 which the thread servicing the queue will be signaled that it should exit.
120 To add a task to the list of tasks queued on a taskqueue, call
121 .Fn taskqueue_enqueue
122 with pointers to the queue and task.
126 then it is simply incremented to reflect the number of times the task
129 the task is added to the list before the first task which has a lower
131 value or at the end of the list if no tasks have a lower priority.
132 Enqueueing a task does not perform any memory allocation which makes
133 it suitable for calling from an interrupt handler.
134 This function will return
136 if the queue is being freed.
139 .Fn taskqueue_enqueue_fast
140 should be used in place of
141 .Fn taskqueue_enqueue
142 when the enqueuing must happen from a fast interrupt handler.
143 This method uses spin locks to avoid the possibility of sleeping in the fast
146 To execute all the tasks on a queue,
150 .Fn taskqueue_run_fast
151 depending on the flavour of the queue.
152 When a task is executed,
153 first it is removed from the queue,
156 is recorded and then the field is zeroed.
159 from the task structure is called with the value of the field
161 as its first argument
164 as its second argument.
169 is called on the task pointer passed to
170 .Fn taskqueue_enqueue .
174 function is used to wait for the task to finish.
175 There is no guarantee that the task will not be
176 enqueued after call to
177 .Fn taskqueue_drain .
185 is part of the given taskqeueue
192 .Fn TASK_INIT "task" "priority" "func" "context"
193 is provided to initialise a
201 are simply copied into the task structure fields and the
206 .Fn TASKQUEUE_DECLARE "name" ,
207 .Fn TASKQUEUE_DEFINE "name" "enqueue" "context" "init" ,
208 .Fn TASKQUEUE_FAST_DEFINE "name" "enqueue" "context" "init" ,
210 .Fn TASKQUEUE_DEFINE_THREAD "name"
211 .Fn TASKQUEUE_FAST_DEFINE_THREAD "name"
212 are used to declare a reference to a global queue, to define the
213 implementation of the queue, and declare a queue that uses its own thread.
216 macro arranges to call
218 with the values of its
223 arguments during system initialisation.
225 .Fn taskqueue_create ,
228 argument to the macro is executed as a C statement,
229 allowing any further initialisation to be performed
230 (such as registering an interrupt handler etc.)
233 .Fn TASKQUEUE_DEFINE_THREAD
234 macro defines a new taskqueue with its own kernel thread to serve tasks.
236 .Vt struct taskqueue *taskqueue_name
237 is used to enqueue tasks onto the queue.
239 .Fn TASKQUEUE_FAST_DEFINE
241 .Fn TASKQUEUE_FAST_DEFINE_THREAD
245 .Fn TASKQUEUE_DEFINE_THREAD
246 respectively but taskqueue is created with
247 .Fn taskqueue_create_fast .
248 .Ss Predefined Task Queues
249 The system provides four global taskqueues,
252 .Va taskqueue_swi_giant ,
254 .Va taskqueue_thread .
257 queue is for swi handlers dispatched from fast interrupt handlers,
258 where sleep mutexes cannot be used.
259 The swi taskqueues are run via a software interrupt mechanism.
262 queue runs without the protection of the
265 .Va taskqueue_swi_giant
266 queue runs with the protection of the
271 runs in a kernel thread context, and tasks run from this thread do
275 If the caller wants to run under
277 he should explicitly acquire and release
279 in his taskqueue handler routine.
283 .Fn taskqueue_enqueue
284 with the value of the global taskqueue variable for the queue you wish to
286 .Va ( taskqueue_swi ,
287 .Va taskqueue_swi_giant ,
289 .Va taskqueue_thread ) .
291 .Fn taskqueue_enqueue_fast
292 for the global taskqueue variable
295 The software interrupt queues can be used,
296 for instance, for implementing interrupt handlers which must perform a
297 significant amount of processing in the handler.
298 The hardware interrupt handler would perform minimal processing of the
299 interrupt and then enqueue a task to finish the work.
300 This reduces to a minimum
301 the amount of time spent with interrupts disabled.
303 The thread queue can be used, for instance, by interrupt level routines
304 that need to call kernel functions that do things that can only be done
305 from a thread context.
306 (e.g., call malloc with the M_WAITOK flag.)
308 Note that tasks queued on shared taskqueues such as
310 may be delayed an indeterminate amount of time before execution.
311 If queueing delays cannot be tolerated then a private taskqueue should
312 be created with a dedicated processing thread.
318 This interface first appeared in
320 There is a similar facility called tqueue in the Linux kernel.
322 This manual page was written by