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18 /* $Id: task.h,v 1.61.332.2 2009/01/18 23:47:41 tbox Exp $ */
28 * \brief The task system provides a lightweight execution context, which is
29 * basically an event queue.
31 * When a task's event queue is non-empty, the
32 * task is runnable. A small work crew of threads, typically one per CPU,
33 * execute runnable tasks by dispatching the events on the tasks' event
34 * queues. Context switching between tasks is fast.
37 * The module ensures appropriate synchronization of data structures it
38 * creates and manipulates.
39 * The caller must ensure that isc_taskmgr_destroy() is called only
40 * once for a given manager.
43 * No anticipated impact.
49 * No anticipated impact.
54 * \section purge Purging and Unsending
56 * Events which have been queued for a task but not delivered may be removed
57 * from the task's event queue by purging or unsending.
59 * With both types, the caller specifies a matching pattern that selects
60 * events based upon their sender, type, and tag.
62 * Purging calls isc_event_free() on the matching events.
64 * Unsending returns a list of events that matched the pattern.
65 * The caller is then responsible for them.
67 * Consumers of events should purge, not unsend.
69 * Producers of events often want to remove events when the caller indicates
70 * it is no longer interested in the object, e.g. by canceling a timer.
71 * Sometimes this can be done by purging, but for some event types, the
72 * calls to isc_event_free() cause deadlock because the event free routine
73 * wants to acquire a lock the caller is already holding. Unsending instead
74 * of purging solves this problem. As a general rule, producers should only
75 * unsend events which they have sent.
83 #include <isc/eventclass.h>
85 #include <isc/stdtime.h>
86 #include <isc/types.h>
89 #define ISC_TASKEVENT_FIRSTEVENT (ISC_EVENTCLASS_TASK + 0)
90 #define ISC_TASKEVENT_SHUTDOWN (ISC_EVENTCLASS_TASK + 1)
91 #define ISC_TASKEVENT_LASTEVENT (ISC_EVENTCLASS_TASK + 65535)
100 isc_task_create(isc_taskmgr_t *manager, unsigned int quantum,
107 *\li If 'quantum' is non-zero, then only that many events can be dispatched
108 * before the task must yield to other tasks waiting to execute. If
109 * quantum is zero, then the default quantum of the task manager will
112 *\li The 'quantum' option may be removed from isc_task_create() in the
113 * future. If this happens, isc_task_getquantum() and
114 * isc_task_setquantum() will be provided.
118 *\li 'manager' is a valid task manager.
120 *\li taskp != NULL && *taskp == NULL
124 *\li On success, '*taskp' is bound to the new task.
130 *\li #ISC_R_UNEXPECTED
131 *\li #ISC_R_SHUTTINGDOWN
135 isc_task_attach(isc_task_t *source, isc_task_t **targetp);
137 * Attach *targetp to source.
141 *\li 'source' is a valid task.
143 *\li 'targetp' points to a NULL isc_task_t *.
147 *\li *targetp is attached to source.
151 isc_task_detach(isc_task_t **taskp);
153 * Detach *taskp from its task.
157 *\li '*taskp' is a valid task.
163 *\li If '*taskp' is the last reference to the task, the task is idle (has
164 * an empty event queue), and has not been shutdown, the task will be
167 *\li If '*taskp' is the last reference to the task and
168 * the task has been shutdown,
169 * all resources used by the task will be freed.
173 isc_task_send(isc_task_t *task, isc_event_t **eventp);
175 * Send '*event' to 'task'.
179 *\li 'task' is a valid task.
180 *\li eventp != NULL && *eventp != NULL.
184 *\li *eventp == NULL.
188 isc_task_sendanddetach(isc_task_t **taskp, isc_event_t **eventp);
190 * Send '*event' to '*taskp' and then detach '*taskp' from its
195 *\li '*taskp' is a valid task.
196 *\li eventp != NULL && *eventp != NULL.
200 *\li *eventp == NULL.
204 *\li If '*taskp' is the last reference to the task, the task is
205 * idle (has an empty event queue), and has not been shutdown,
206 * the task will be shutdown.
208 *\li If '*taskp' is the last reference to the task and
209 * the task has been shutdown,
210 * all resources used by the task will be freed.
215 isc_task_purgerange(isc_task_t *task, void *sender, isc_eventtype_t first,
216 isc_eventtype_t last, void *tag);
218 * Purge events from a task's event queue.
222 *\li 'task' is a valid task.
228 *\li Events in the event queue of 'task' whose sender is 'sender', whose
229 * type is >= first and <= last, and whose tag is 'tag' will be purged,
230 * unless they are marked as unpurgable.
232 *\li A sender of NULL will match any sender. A NULL tag matches any
237 *\li The number of events purged.
241 isc_task_purge(isc_task_t *task, void *sender, isc_eventtype_t type,
244 * Purge events from a task's event queue.
248 *\li This function is equivalent to
251 * isc_task_purgerange(task, sender, type, type, tag);
256 *\li 'task' is a valid task.
260 *\li Events in the event queue of 'task' whose sender is 'sender', whose
261 * type is 'type', and whose tag is 'tag' will be purged, unless they
262 * are marked as unpurgable.
264 *\li A sender of NULL will match any sender. A NULL tag matches any
269 *\li The number of events purged.
273 isc_task_purgeevent(isc_task_t *task, isc_event_t *event);
275 * Purge 'event' from a task's event queue.
277 * XXXRTH: WARNING: This method may be removed before beta.
281 *\li If 'event' is on the task's event queue, it will be purged,
282 * unless it is marked as unpurgeable. 'event' does not have to be
283 * on the task's event queue; in fact, it can even be an invalid
284 * pointer. Purging only occurs if the event is actually on the task's
287 * \li Purging never changes the state of the task.
291 *\li 'task' is a valid task.
295 *\li 'event' is not in the event queue for 'task'.
299 *\li #ISC_TRUE The event was purged.
300 *\li #ISC_FALSE The event was not in the event queue,
301 * or was marked unpurgeable.
305 isc_task_unsendrange(isc_task_t *task, void *sender, isc_eventtype_t first,
306 isc_eventtype_t last, void *tag, isc_eventlist_t *events);
308 * Remove events from a task's event queue.
312 *\li 'task' is a valid task.
316 *\li *events is a valid list.
320 *\li Events in the event queue of 'task' whose sender is 'sender', whose
321 * type is >= first and <= last, and whose tag is 'tag' will be dequeued
322 * and appended to *events.
324 *\li A sender of NULL will match any sender. A NULL tag matches any
329 *\li The number of events unsent.
333 isc_task_unsend(isc_task_t *task, void *sender, isc_eventtype_t type,
334 void *tag, isc_eventlist_t *events);
336 * Remove events from a task's event queue.
340 *\li This function is equivalent to
343 * isc_task_unsendrange(task, sender, type, type, tag, events);
348 *\li 'task' is a valid task.
350 *\li *events is a valid list.
354 *\li Events in the event queue of 'task' whose sender is 'sender', whose
355 * type is 'type', and whose tag is 'tag' will be dequeued and appended
360 *\li The number of events unsent.
364 isc_task_onshutdown(isc_task_t *task, isc_taskaction_t action,
367 * Send a shutdown event with action 'action' and argument 'arg' when
368 * 'task' is shutdown.
372 *\li Shutdown events are posted in LIFO order.
376 *\li 'task' is a valid task.
378 *\li 'action' is a valid task action.
382 *\li When the task is shutdown, shutdown events requested with
383 * isc_task_onshutdown() will be appended to the task's event queue.
390 *\li #ISC_R_TASKSHUTTINGDOWN Task is shutting down.
394 isc_task_shutdown(isc_task_t *task);
400 *\li Shutting down a task causes any shutdown events requested with
401 * isc_task_onshutdown() to be posted (in LIFO order). The task
402 * moves into a "shutting down" mode which prevents further calls
403 * to isc_task_onshutdown().
405 *\li Trying to shutdown a task that has already been shutdown has no
410 *\li 'task' is a valid task.
414 *\li Any shutdown events requested with isc_task_onshutdown() have been
415 * posted (in LIFO order).
419 isc_task_destroy(isc_task_t **taskp);
425 *\li This call is equivalent to:
428 * isc_task_shutdown(*taskp);
429 * isc_task_detach(taskp);
434 * '*taskp' is a valid task.
438 *\li Any shutdown events requested with isc_task_onshutdown() have been
439 * posted (in LIFO order).
443 *\li If '*taskp' is the last reference to the task,
444 * all resources used by the task will be freed.
448 isc_task_setname(isc_task_t *task, const char *name, void *tag);
454 *\li Only the first 15 characters of 'name' will be copied.
456 *\li Naming a task is currently only useful for debugging purposes.
460 *\li 'task' is a valid task.
464 isc_task_getname(isc_task_t *task);
466 * Get the name of 'task', as previously set using isc_task_setname().
469 *\li This function is for debugging purposes only.
472 *\li 'task' is a valid task.
475 *\li A non-NULL pointer to a null-terminated string.
476 * If the task has not been named, the string is
482 isc_task_gettag(isc_task_t *task);
484 * Get the tag value for 'task', as previously set using isc_task_settag().
487 *\li This function is for debugging purposes only.
490 *\li 'task' is a valid task.
494 isc_task_beginexclusive(isc_task_t *task);
496 * Request exclusive access for 'task', which must be the calling
497 * task. Waits for any other concurrently executing tasks to finish their
498 * current event, and prevents any new events from executing in any of the
499 * tasks sharing a task manager with 'task'.
501 * The exclusive access must be relinquished by calling
502 * isc_task_endexclusive() before returning from the current event handler.
505 *\li 'task' is the calling task.
508 *\li #ISC_R_SUCCESS The current task now has exclusive access.
509 *\li #ISC_R_LOCKBUSY Another task has already requested exclusive
514 isc_task_endexclusive(isc_task_t *task);
516 * Relinquish the exclusive access obtained by isc_task_beginexclusive(),
517 * allowing other tasks to execute.
520 *\li 'task' is the calling task, and has obtained
521 * exclusive access by calling isc_task_spl().
525 isc_task_getcurrenttime(isc_task_t *task, isc_stdtime_t *t);
527 * Provide the most recent timestamp on the task. The timestamp is considered
528 * as the "current time" in the second-order granularity.
531 *\li 'task' is a valid task.
532 *\li 't' is a valid non NULL pointer.
535 *\li '*t' has the "current time".
543 isc_taskmgr_create(isc_mem_t *mctx, unsigned int workers,
544 unsigned int default_quantum, isc_taskmgr_t **managerp);
546 * Create a new task manager.
550 *\li 'workers' in the number of worker threads to create. In general,
551 * the value should be close to the number of processors in the system.
552 * The 'workers' value is advisory only. An attempt will be made to
553 * create 'workers' threads, but if at least one thread creation
554 * succeeds, isc_taskmgr_create() may return ISC_R_SUCCESS.
556 *\li If 'default_quantum' is non-zero, then it will be used as the default
557 * quantum value when tasks are created. If zero, then an implementation
558 * defined default quantum will be used.
562 *\li 'mctx' is a valid memory context.
566 *\li managerp != NULL && *managerp == NULL
570 *\li On success, '*managerp' will be attached to the newly created task
577 *\li #ISC_R_NOTHREADS No threads could be created.
578 *\li #ISC_R_UNEXPECTED An unexpected error occurred.
582 isc_taskmgr_destroy(isc_taskmgr_t **managerp);
584 * Destroy '*managerp'.
588 *\li Calling isc_taskmgr_destroy() will shutdown all tasks managed by
589 * *managerp that haven't already been shutdown. The call will block
590 * until all tasks have entered the done state.
592 *\li isc_taskmgr_destroy() must not be called by a task event action,
593 * because it would block forever waiting for the event action to
594 * complete. An event action that wants to cause task manager shutdown
595 * should request some non-event action thread of execution to do the
596 * shutdown, e.g. by signaling a condition variable or using
597 * isc_app_shutdown().
599 *\li Task manager references are not reference counted, so the caller
600 * must ensure that no attempt will be made to use the manager after
601 * isc_taskmgr_destroy() returns.
605 *\li '*managerp' is a valid task manager.
607 *\li isc_taskmgr_destroy() has not be called previously on '*managerp'.
611 *\li All resources used by the task manager, and any tasks it managed,
618 isc_taskmgr_renderxml(isc_taskmgr_t *mgr, xmlTextWriterPtr writer);
624 #endif /* ISC_TASK_H */