task.c 20 KB
Newer Older
Bob Halley's avatar
base  
Bob Halley committed
1

Bob Halley's avatar
Bob Halley committed
2 3
#include "attribute.h"

Bob Halley's avatar
base  
Bob Halley committed
4 5
#include <isc/assertions.h>

Bob Halley's avatar
Bob Halley committed
6
#include <isc/thread.h>
7 8 9
#include <isc/mutex.h>
#include <isc/condition.h>

Bob Halley's avatar
Bob Halley committed
10
#include <isc/task.h>
Bob Halley's avatar
base  
Bob Halley committed
11

Bob Halley's avatar
Bob Halley committed
12 13 14 15

/***
 *** General Macros.
 ***/
Bob Halley's avatar
base  
Bob Halley committed
16

Bob Halley's avatar
update  
Bob Halley committed
17
/*
Bob Halley's avatar
update  
Bob Halley committed
18 19 20 21 22
 * We use macros instead of calling the os_ routines directly because
 * the capital letters make the locking stand out.
 *
 * We INSIST that they succeed since there's no way for us to continue
 * if they fail.
Bob Halley's avatar
update  
Bob Halley committed
23
 */
Bob Halley's avatar
update  
Bob Halley committed
24 25 26 27
#define LOCK(lp)		INSIST(os_mutex_lock((lp)))
#define UNLOCK(lp)		INSIST(os_mutex_unlock((lp)))
#define WAIT(cvp, lp)		INSIST(os_condition_wait((cvp), (lp)))
#define BROADCAST(cvp)		INSIST(os_condition_broadcast((cvp)))
Bob Halley's avatar
base  
Bob Halley committed
28

Bob Halley's avatar
Bob Halley committed
29
#ifdef ISC_TASK_TRACE
Bob Halley's avatar
Bob Halley committed
30 31
#define XTRACE(m)		printf("%s task %p thread %p\n", (m), \
				       task, os_thread_self())
Bob Halley's avatar
Bob Halley committed
32 33 34
#else
#define XTRACE(m)
#endif
Bob Halley's avatar
base  
Bob Halley committed
35

Bob Halley's avatar
Bob Halley committed
36 37

/***
Bob Halley's avatar
Bob Halley committed
38
 *** Types.
Bob Halley's avatar
Bob Halley committed
39 40
 ***/

Bob Halley's avatar
Bob Halley committed
41 42 43 44 45 46 47 48 49
typedef enum {
	task_state_idle, task_state_ready, task_state_running,
	task_state_shutdown
} task_state_t;

#define TASK_MAGIC			0x5441534BU	/* TASK. */
#define VALID_TASK(t)			((t) != NULL && \
					 (t)->magic == TASK_MAGIC)

Bob Halley's avatar
Bob Halley committed
50
struct isc_task {
Bob Halley's avatar
Bob Halley committed
51 52
	/* Not locked. */
	unsigned int			magic;
Bob Halley's avatar
Bob Halley committed
53
	isc_taskmgr_t			manager;
Bob Halley's avatar
Bob Halley committed
54 55 56 57
	os_mutex_t			lock;
	/* Locked by task lock. */
	task_state_t			state;
	unsigned int			references;
Bob Halley's avatar
Bob Halley committed
58
	isc_eventlist_t			events;
Bob Halley's avatar
Bob Halley committed
59
	unsigned int			quantum;
Bob Halley's avatar
Bob Halley committed
60
	isc_boolean_t			enqueue_allowed;
Bob Halley's avatar
Bob Halley committed
61
	isc_event_t			shutdown_event;
Bob Halley's avatar
Bob Halley committed
62
	/* Locked by task manager lock. */
Bob Halley's avatar
Bob Halley committed
63 64
	LINK(struct isc_task)		link;
	LINK(struct isc_task)		ready_link;
Bob Halley's avatar
Bob Halley committed
65 66 67 68 69 70
};

#define TASK_MANAGER_MAGIC		0x54534B4DU	/* TSKM. */
#define VALID_MANAGER(m)		((m) != NULL && \
					 (m)->magic == TASK_MANAGER_MAGIC)

Bob Halley's avatar
Bob Halley committed
71
struct isc_taskmgr {
Bob Halley's avatar
Bob Halley committed
72 73
	/* Not locked. */
	unsigned int			magic;
Bob Halley's avatar
Bob Halley committed
74
	isc_memctx_t			mctx;
Bob Halley's avatar
Bob Halley committed
75 76 77
	os_mutex_t			lock;
	/* Locked by task manager lock. */
	unsigned int			default_quantum;
Bob Halley's avatar
Bob Halley committed
78 79
	LIST(struct isc_task)		tasks;
	LIST(struct isc_task)		ready_tasks;
Bob Halley's avatar
Bob Halley committed
80
	os_condition_t			work_available;
Bob Halley's avatar
Bob Halley committed
81
	isc_boolean_t			exiting;
Bob Halley's avatar
Bob Halley committed
82 83 84
	unsigned int			workers;
	os_condition_t			no_workers;
};
Bob Halley's avatar
Bob Halley committed
85

Bob Halley's avatar
Bob Halley committed
86 87
#define DEFAULT_DEFAULT_QUANTUM		5
#define FINISHED(m)			((m)->exiting && EMPTY((m)->tasks))
Bob Halley's avatar
Bob Halley committed
88

Bob Halley's avatar
update  
Bob Halley committed
89 90 91 92 93

/***
 *** Events.
 ***/

Bob Halley's avatar
Bob Halley committed
94
static inline isc_event_t
Bob Halley's avatar
Bob Halley committed
95
event_allocate(isc_memctx_t mctx, void *sender, isc_eventtype_t type,
Bob Halley's avatar
Bob Halley committed
96
	       isc_taskaction_t action, void *arg, size_t size)
Bob Halley's avatar
update  
Bob Halley committed
97
{
Bob Halley's avatar
Bob Halley committed
98
	isc_event_t event;
Bob Halley's avatar
update  
Bob Halley committed
99

Bob Halley's avatar
Bob Halley committed
100
	event = isc_mem_get(mctx, size);
Bob Halley's avatar
update  
Bob Halley committed
101 102 103 104
	if (event == NULL)
		return (NULL);
	event->mctx = mctx;
	event->size = size;
Bob Halley's avatar
Bob Halley committed
105
	event->sender = sender;
Bob Halley's avatar
update  
Bob Halley committed
106 107 108 109 110 111 112
	event->type = type;
	event->action = action;
	event->arg = arg;

	return (event);
}

Bob Halley's avatar
Bob Halley committed
113
isc_event_t
Bob Halley's avatar
Bob Halley committed
114 115
isc_event_allocate(isc_memctx_t mctx, void *sender, isc_eventtype_t type,
		   isc_taskaction_t action, void *arg, size_t size)
Bob Halley's avatar
update  
Bob Halley committed
116
{
Bob Halley's avatar
Bob Halley committed
117
	if (size < sizeof (struct isc_event))
Bob Halley's avatar
update  
Bob Halley committed
118 119 120 121 122 123
		return (NULL);
	if (type < 0)
		return (NULL);
	if (action == NULL)
		return (NULL);

Bob Halley's avatar
Bob Halley committed
124
	return (event_allocate(mctx, sender, type, action, arg, size));
Bob Halley's avatar
update  
Bob Halley committed
125 126 127
}

void
Bob Halley's avatar
Bob Halley committed
128 129
isc_event_free(isc_event_t *eventp) {
	isc_event_t event;
Bob Halley's avatar
update  
Bob Halley committed
130 131 132 133 134
	
	REQUIRE(eventp != NULL);
	event = *eventp;
	REQUIRE(event != NULL);

Bob Halley's avatar
Bob Halley committed
135
	isc_mem_put(event->mctx, event, event->size);
Bob Halley's avatar
update  
Bob Halley committed
136 137 138 139

	*eventp = NULL;
}

Bob Halley's avatar
base  
Bob Halley committed
140 141 142 143 144
/***
 *** Tasks.
 ***/

static void
Bob Halley's avatar
Bob Halley committed
145 146
task_free(isc_task_t task) {
	isc_taskmgr_t manager = task->manager;
Bob Halley's avatar
base  
Bob Halley committed
147

Bob Halley's avatar
Bob Halley committed
148
	XTRACE("free task");
Bob Halley's avatar
base  
Bob Halley committed
149 150 151 152 153 154 155 156 157 158 159 160 161 162
	REQUIRE(EMPTY(task->events));

	LOCK(&manager->lock);
	UNLINK(manager->tasks, task, link);
	if (FINISHED(manager)) {
		/*
		 * All tasks have completed and the
		 * task manager is exiting.  Wake up
		 * any idle worker threads so they
		 * can exit.
		 */
		BROADCAST(&manager->work_available);
	}
	UNLOCK(&manager->lock);
Bob Halley's avatar
update  
Bob Halley committed
163
	(void)os_mutex_destroy(&task->lock);
Bob Halley's avatar
update  
Bob Halley committed
164
	if (task->shutdown_event != NULL)
Bob Halley's avatar
Bob Halley committed
165
		isc_event_free(&task->shutdown_event);
Bob Halley's avatar
base  
Bob Halley committed
166
	task->magic = 0;
Bob Halley's avatar
Bob Halley committed
167
	isc_mem_put(manager->mctx, task, sizeof *task);
Bob Halley's avatar
base  
Bob Halley committed
168 169
}

Bob Halley's avatar
Bob Halley committed
170
isc_boolean_t
Bob Halley's avatar
Bob Halley committed
171 172
isc_task_create(isc_taskmgr_t manager, isc_taskaction_t shutdown_action,
		void *shutdown_arg, unsigned int quantum, isc_task_t *taskp)
Bob Halley's avatar
Bob Halley committed
173
{
Bob Halley's avatar
Bob Halley committed
174
	isc_task_t task;
Bob Halley's avatar
base  
Bob Halley committed
175 176 177 178

	REQUIRE(VALID_MANAGER(manager));
	REQUIRE(taskp != NULL && *taskp == NULL);

Bob Halley's avatar
Bob Halley committed
179
	task = isc_mem_get(manager->mctx, sizeof *task);
Bob Halley's avatar
base  
Bob Halley committed
180
	if (task == NULL)
Bob Halley's avatar
Bob Halley committed
181
		return (ISC_FALSE);
Bob Halley's avatar
base  
Bob Halley committed
182 183 184

	task->magic = TASK_MAGIC;
	task->manager = manager;
Bob Halley's avatar
update  
Bob Halley committed
185
	if (!os_mutex_init(&task->lock)) {
Bob Halley's avatar
Bob Halley committed
186
		isc_mem_put(manager->mctx, task, sizeof *task);
Bob Halley's avatar
Bob Halley committed
187
		return (ISC_FALSE);
Bob Halley's avatar
update  
Bob Halley committed
188
	}
Bob Halley's avatar
base  
Bob Halley committed
189 190 191 192
	task->state = task_state_idle;
	task->references = 1;
	INIT_LIST(task->events);
	task->quantum = quantum;
Bob Halley's avatar
Bob Halley committed
193
	task->enqueue_allowed = ISC_TRUE;
Bob Halley's avatar
update  
Bob Halley committed
194
	task->shutdown_event = event_allocate(manager->mctx,
Bob Halley's avatar
Bob Halley committed
195
					      NULL,
Bob Halley's avatar
Bob Halley committed
196
					      ISC_TASKEVENT_SHUTDOWN,
Bob Halley's avatar
update  
Bob Halley committed
197 198 199 200 201
					      shutdown_action,
					      shutdown_arg,
					      sizeof *task->shutdown_event);
	if (task->shutdown_event == NULL) {
		(void)os_mutex_destroy(&task->lock);
Bob Halley's avatar
Bob Halley committed
202
		isc_mem_put(manager->mctx, task, sizeof *task);
Bob Halley's avatar
Bob Halley committed
203
		return (ISC_FALSE);
Bob Halley's avatar
update  
Bob Halley committed
204
	}
Bob Halley's avatar
base  
Bob Halley committed
205 206 207 208 209 210 211 212 213 214 215
	INIT_LINK(task, link);
	INIT_LINK(task, ready_link);

	LOCK(&manager->lock);
	if (task->quantum == 0)
		task->quantum = manager->default_quantum;
	APPEND(manager->tasks, task, link);
	UNLOCK(&manager->lock);

	*taskp = task;

Bob Halley's avatar
Bob Halley committed
216
	return (ISC_TRUE);
Bob Halley's avatar
base  
Bob Halley committed
217 218
}

Bob Halley's avatar
update  
Bob Halley committed
219
void
Bob Halley's avatar
Bob Halley committed
220
isc_task_attach(isc_task_t task, isc_task_t *taskp) {
Bob Halley's avatar
base  
Bob Halley committed
221 222 223 224 225 226 227 228 229 230 231

	REQUIRE(VALID_TASK(task));
	REQUIRE(taskp != NULL && *taskp == NULL);

	LOCK(&task->lock);
	task->references++;
	UNLOCK(&task->lock);

	*taskp = task;
}

Bob Halley's avatar
Bob Halley committed
232
void
Bob Halley's avatar
Bob Halley committed
233
isc_task_detach(isc_task_t *taskp) {
Bob Halley's avatar
Bob Halley committed
234
	isc_boolean_t free_task = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
235
	isc_task_t task;
Bob Halley's avatar
base  
Bob Halley committed
236

Bob Halley's avatar
Bob Halley committed
237
	XTRACE("isc_task_detach");
Bob Halley's avatar
base  
Bob Halley committed
238 239 240 241 242 243 244 245

	REQUIRE(taskp != NULL);
	task = *taskp;
	REQUIRE(VALID_TASK(task));

	LOCK(&task->lock);
	REQUIRE(task->references > 0);
	task->references--;
246
	if (task->state == task_state_shutdown && task->references == 0)
Bob Halley's avatar
Bob Halley committed
247
		free_task = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
248 249 250 251 252 253 254 255
	UNLOCK(&task->lock);

	if (free_task)
		task_free(task);

	*taskp = NULL;
}

Bob Halley's avatar
Bob Halley committed
256
isc_boolean_t
Bob Halley's avatar
Bob Halley committed
257
isc_task_send(isc_task_t task, isc_event_t *eventp) {
Bob Halley's avatar
Bob Halley committed
258 259
	isc_boolean_t was_idle = ISC_FALSE;
	isc_boolean_t discard = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
260
	isc_event_t event;
Bob Halley's avatar
base  
Bob Halley committed
261 262

	REQUIRE(VALID_TASK(task));
Bob Halley's avatar
update  
Bob Halley committed
263 264
	REQUIRE(eventp != NULL);
	event = *eventp;
Bob Halley's avatar
base  
Bob Halley committed
265
	REQUIRE(event != NULL);
Bob Halley's avatar
Bob Halley committed
266 267
	REQUIRE(event->sender != NULL);
	REQUIRE(event->type > 0);
Bob Halley's avatar
base  
Bob Halley committed
268

Bob Halley's avatar
Bob Halley committed
269
	XTRACE("sending");
Bob Halley's avatar
base  
Bob Halley committed
270 271 272 273 274 275
	/*
	 * We're trying hard to hold locks for as short a time as possible.
	 * We're also trying to hold as few locks as possible.  This is why
	 * some processing is deferred until after a lock is released.
	 */
	LOCK(&task->lock);
Bob Halley's avatar
update  
Bob Halley committed
276
	if (task->enqueue_allowed) {
Bob Halley's avatar
base  
Bob Halley committed
277
		if (task->state == task_state_idle) {
Bob Halley's avatar
Bob Halley committed
278
			was_idle = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
279 280 281 282 283 284 285
			INSIST(EMPTY(task->events));
			task->state = task_state_ready;
		}
		INSIST(task->state == task_state_ready ||
		       task->state == task_state_running);
		ENQUEUE(task->events, event, link);
	} else
Bob Halley's avatar
Bob Halley committed
286
		discard = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
287 288 289
	UNLOCK(&task->lock);

	if (discard) {
Bob Halley's avatar
Bob Halley committed
290
		isc_event_free(&event);
Bob Halley's avatar
update  
Bob Halley committed
291
		*eventp = NULL;
Bob Halley's avatar
Bob Halley committed
292
		return (ISC_TRUE);
Bob Halley's avatar
base  
Bob Halley committed
293 294 295
	}

	if (was_idle) {
Bob Halley's avatar
Bob Halley committed
296
		isc_boolean_t need_wakeup = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
297
		isc_taskmgr_t manager;
Bob Halley's avatar
base  
Bob Halley committed
298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321

		/*
		 * We need to add this task to the ready queue.
		 *
		 * We've waited until now to do it, rather than doing it
		 * while holding the task lock, because we don't want to
		 * block while holding the task lock.
		 *
		 * We've changed the state to ready, so no one else will
		 * be trying to add this task to the ready queue.  It
		 * thus doesn't matter if more events have been added to
		 * the queue after we gave up the task lock.
		 *
		 * Shutting down a task requires posting a shutdown event
		 * to the task's queue and then executing it, so there's
		 * no way the task can disappear.  A task is always on the
		 * task manager's 'tasks' list, so the task manager can
		 * always post a shutdown event to all tasks if it is
		 * requested to shutdown.
		 */
		manager = task->manager;
		INSIST(VALID_MANAGER(manager));
		LOCK(&manager->lock);
		if (EMPTY(manager->ready_tasks))
Bob Halley's avatar
Bob Halley committed
322
			need_wakeup = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
323 324 325 326 327 328 329 330 331 332 333 334
		ENQUEUE(manager->ready_tasks, task, ready_link);
		UNLOCK(&manager->lock);

		/*
		 * If the runnable queue is empty, the worker threads could
		 * either be executing tasks or waiting for something to do.
		 * We wakeup anyone who is sleeping.
		 */
		if (need_wakeup)
			BROADCAST(&manager->work_available);
	}

Bob Halley's avatar
update  
Bob Halley committed
335 336
	*eventp = NULL;

Bob Halley's avatar
Bob Halley committed
337
	XTRACE("sent");
Bob Halley's avatar
Bob Halley committed
338
	return (ISC_TRUE);
Bob Halley's avatar
base  
Bob Halley committed
339 340
}

Bob Halley's avatar
Bob Halley committed
341
void
Bob Halley's avatar
Bob Halley committed
342 343 344
isc_task_purge(isc_task_t task, void *sender, isc_eventtype_t type) {
	isc_event_t event, next_event;
	isc_eventlist_t purgeable;
Bob Halley's avatar
Bob Halley committed
345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373

	REQUIRE(VALID_TASK(task));
	REQUIRE(type >= 0);

	/*
	 * Purge events matching 'sender' and 'type'.  sender == NULL means
	 * "any sender".  type == NULL means any type.  Task manager events
	 * cannot be purged.
	 */

	INIT_LIST(purgeable);

	LOCK(&task->lock);
	for (event = HEAD(task->events);
	     event != NULL;
	     event = next_event) {
		next_event = NEXT(event, link);
		if ((sender == NULL || event->sender == sender) &&
		    ((type == 0 && event->type > 0) || event->type == type)) {
			DEQUEUE(task->events, event, link);
			ENQUEUE(purgeable, event, link);
		}
	}
	UNLOCK(&task->lock);

	for (event = HEAD(purgeable);
	     event != NULL;
	     event = next_event) {
		next_event = NEXT(event, link);
Bob Halley's avatar
Bob Halley committed
374
		isc_event_free(&event);
Bob Halley's avatar
Bob Halley committed
375 376 377
	}
}

Bob Halley's avatar
Bob Halley committed
378
void
Bob Halley's avatar
Bob Halley committed
379
isc_task_shutdown(isc_task_t task) {
Bob Halley's avatar
Bob Halley committed
380 381
	isc_boolean_t was_idle = ISC_FALSE;
	isc_boolean_t discard = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
382 383 384 385

	REQUIRE(VALID_TASK(task));

	/*
Bob Halley's avatar
Bob Halley committed
386
	 * This routine is very similar to isc_task_send_event() above.
Bob Halley's avatar
base  
Bob Halley committed
387 388 389
	 */

	LOCK(&task->lock);
Bob Halley's avatar
update  
Bob Halley committed
390
	if (task->enqueue_allowed) {
Bob Halley's avatar
base  
Bob Halley committed
391
		if (task->state == task_state_idle) {
Bob Halley's avatar
Bob Halley committed
392
			was_idle = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
393 394 395 396 397
			INSIST(EMPTY(task->events));
			task->state = task_state_ready;
		}
		INSIST(task->state == task_state_ready ||
		       task->state == task_state_running);
Bob Halley's avatar
update  
Bob Halley committed
398 399 400
		INSIST(task->shutdown_event != NULL);
		ENQUEUE(task->events, task->shutdown_event, link);
		task->shutdown_event = NULL;
Bob Halley's avatar
Bob Halley committed
401
		task->enqueue_allowed = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
402
	} else
Bob Halley's avatar
Bob Halley committed
403
		discard = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
404 405
	UNLOCK(&task->lock);

Bob Halley's avatar
Bob Halley committed
406
	if (discard)
Bob Halley's avatar
Bob Halley committed
407
		return;
Bob Halley's avatar
base  
Bob Halley committed
408 409

	if (was_idle) {
Bob Halley's avatar
Bob Halley committed
410
		isc_boolean_t need_wakeup = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
411
		isc_taskmgr_t manager;
Bob Halley's avatar
base  
Bob Halley committed
412 413 414 415 416

		manager = task->manager;
		INSIST(VALID_MANAGER(manager));
		LOCK(&manager->lock);
		if (EMPTY(manager->ready_tasks))
Bob Halley's avatar
Bob Halley committed
417
			need_wakeup = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
418 419 420 421 422 423
		ENQUEUE(manager->ready_tasks, task, ready_link);
		UNLOCK(&manager->lock);

		if (need_wakeup)
			BROADCAST(&manager->work_available);
	}
Bob Halley's avatar
Bob Halley committed
424
}
Bob Halley's avatar
base  
Bob Halley committed
425

Bob Halley's avatar
Bob Halley committed
426
void
Bob Halley's avatar
Bob Halley committed
427
isc_task_destroy(isc_task_t *taskp) {
Bob Halley's avatar
Bob Halley committed
428 429 430

	REQUIRE(taskp != NULL);

Bob Halley's avatar
Bob Halley committed
431 432
	isc_task_shutdown(*taskp);
	isc_task_detach(taskp);
Bob Halley's avatar
base  
Bob Halley committed
433 434 435
}


Bob Halley's avatar
Bob Halley committed
436

Bob Halley's avatar
base  
Bob Halley committed
437 438 439 440 441
/***
 *** Task Manager.
 ***/

static
Bob Halley's avatar
Bob Halley committed
442 443 444
void *run(void *uap) {
	isc_taskmgr_t manager = uap;
	isc_task_t task;
Bob Halley's avatar
Bob Halley committed
445
	isc_boolean_t no_workers = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
446

Bob Halley's avatar
Bob Halley committed
447
	XTRACE("start");
Bob Halley's avatar
base  
Bob Halley committed
448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504

	REQUIRE(VALID_MANAGER(manager));

	/*
	 * Again we're trying to hold the lock for as short a time as possible
	 * and to do as little locking and unlocking as possible.
	 * 
	 * In both while loops, the appropriate lock must be held before the
	 * while body starts.  Code which acquired the lock at the top of
	 * the loop would be more readable, but would result in a lot of
	 * extra locking.  Compare:
	 *
	 * Straightforward:
	 *
	 *	LOCK();
	 *	...
	 *	UNLOCK();
	 *	while (expression) {
	 *		LOCK();
	 *		...
	 *		UNLOCK();
	 *
	 *	       	Unlocked part here...
	 *
	 *		LOCK();
	 *		...
	 *		UNLOCK();
	 *	}
	 *
	 * Note how if the loop continues we unlock and then immediately lock.
	 * For N iterations of the loop, this code does 2N+1 locks and 2N+1
	 * unlocks.  Also note that the lock is not held when the while
	 * condition is tested, which may or may not be important, depending
	 * on the expression.
	 * 
	 * As written:
	 *
	 *	LOCK();
	 *	while (expression) {
	 *		...
	 *		UNLOCK();
	 *
	 *	       	Unlocked part here...
	 *
	 *		LOCK();
	 *		...
	 *	}
	 *	UNLOCK();
	 *
	 * For N iterations of the loop, this code does N+1 locks and N+1
	 * unlocks.  The while expression is always protected by the lock.
	 */

	LOCK(&manager->lock);
	while (!FINISHED(manager)) {
		/*
		 * For reasons similar to those given in the comment in
Bob Halley's avatar
Bob Halley committed
505
		 * isc_task_send_event() above, it is safe for us to dequeue
Bob Halley's avatar
base  
Bob Halley committed
506 507 508 509 510
		 * the task while only holding the manager lock, and then
		 * change the task to running state while only holding the
		 * task lock.
		 */
		while (EMPTY(manager->ready_tasks) && !FINISHED(manager)) {
Bob Halley's avatar
Bob Halley committed
511
			XTRACE("wait");
Bob Halley's avatar
base  
Bob Halley committed
512
			WAIT(&manager->work_available, &manager->lock);
Bob Halley's avatar
Bob Halley committed
513
			XTRACE("awake");
Bob Halley's avatar
base  
Bob Halley committed
514
		}
Bob Halley's avatar
Bob Halley committed
515
		XTRACE("working");
Bob Halley's avatar
base  
Bob Halley committed
516 517 518
		
		task = HEAD(manager->ready_tasks);
		if (task != NULL) {
Bob Halley's avatar
Bob Halley committed
519
			unsigned int dispatch_count = 0;
Bob Halley's avatar
Bob Halley committed
520 521 522 523 524
			isc_boolean_t done = ISC_FALSE;
			isc_boolean_t requeue = ISC_FALSE;
			isc_boolean_t wants_shutdown;
			isc_boolean_t is_shutdown;
			isc_boolean_t free_task = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
525 526
			isc_event_t event;
			isc_eventlist_t remaining_events;
Bob Halley's avatar
Bob Halley committed
527
			isc_boolean_t discard_remaining = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
528 529 530 531 532 533 534 535 536 537 538 539

			INSIST(VALID_TASK(task));

			/*
			 * Note we only unlock the manager lock if we actually
			 * have a task to do.  We must reacquire the manager 
			 * lock before exiting the 'if (task != NULL)' block.
			 */
			DEQUEUE(manager->ready_tasks, task, ready_link);
			UNLOCK(&manager->lock);

			LOCK(&task->lock);
Bob Halley's avatar
Bob Halley committed
540 541 542 543 544 545 546 547
			INSIST(task->state == task_state_ready);
			if (EMPTY(task->events)) {
				/*
				 * The task became runnable, but all events
				 * in the run queue were subsequently purged.
				 * Put the task to sleep.
				 */
				task->state = task_state_idle;
Bob Halley's avatar
Bob Halley committed
548
				done = ISC_TRUE;
Bob Halley's avatar
Bob Halley committed
549 550 551
				XTRACE("ready but empty");
			} else
				task->state = task_state_running;
Bob Halley's avatar
base  
Bob Halley committed
552
			while (!done) {
Bob Halley's avatar
update  
Bob Halley committed
553 554 555
				INSIST(!EMPTY(task->events));
				event = HEAD(task->events);
				DEQUEUE(task->events, event, link);
Bob Halley's avatar
base  
Bob Halley committed
556 557
				UNLOCK(&task->lock);

Bob Halley's avatar
Bob Halley committed
558
				if (event->type == ISC_TASKEVENT_SHUTDOWN)
Bob Halley's avatar
Bob Halley committed
559
					is_shutdown = ISC_TRUE;
Bob Halley's avatar
update  
Bob Halley committed
560
				else
Bob Halley's avatar
Bob Halley committed
561
					is_shutdown = ISC_FALSE;
Bob Halley's avatar
update  
Bob Halley committed
562

Bob Halley's avatar
base  
Bob Halley committed
563 564 565
				/*
				 * Execute the event action.
				 */
Bob Halley's avatar
Bob Halley committed
566
				XTRACE("execute action");
Bob Halley's avatar
update  
Bob Halley committed
567 568 569
				if (event->action != NULL)
					wants_shutdown =
						(event->action)(task, event);
Bob Halley's avatar
base  
Bob Halley committed
570
				else
Bob Halley's avatar
Bob Halley committed
571
					wants_shutdown = ISC_FALSE;
Bob Halley's avatar
Bob Halley committed
572
				dispatch_count++;
Bob Halley's avatar
update  
Bob Halley committed
573
				
Bob Halley's avatar
Bob Halley committed
574
				isc_event_free(&event);
Bob Halley's avatar
base  
Bob Halley committed
575 576

				LOCK(&task->lock);
Bob Halley's avatar
update  
Bob Halley committed
577
				if (wants_shutdown || is_shutdown) {
Bob Halley's avatar
Bob Halley committed
578
					/*
Bob Halley's avatar
update  
Bob Halley committed
579 580 581 582
					 * The event action has either
					 * requested shutdown, or the event
					 * we just executed was the shutdown
					 * event.
Bob Halley's avatar
Bob Halley committed
583 584 585 586 587 588 589 590
					 *
					 * Since no more events can be
					 * delivered to the task, we purge
					 * any remaining events (but defer
					 * freeing them until we've released
					 * the lock).
					 */
					XTRACE("wants shutdown");
Bob Halley's avatar
base  
Bob Halley committed
591 592 593 594
					if (!EMPTY(task->events)) {
						remaining_events =
							task->events;
						INIT_LIST(task->events);
Bob Halley's avatar
Bob Halley committed
595
						discard_remaining = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
596 597
					}
					if (task->references == 0)
Bob Halley's avatar
Bob Halley committed
598
						free_task = ISC_TRUE;
Bob Halley's avatar
Bob Halley committed
599
					task->state = task_state_shutdown;
Bob Halley's avatar
Bob Halley committed
600 601
					task->enqueue_allowed = ISC_FALSE;
					done = ISC_TRUE;
Bob Halley's avatar
update  
Bob Halley committed
602
				} else if (EMPTY(task->events)) {
Bob Halley's avatar
Bob Halley committed
603 604 605
					/*
					 * Nothing else to do for this task.
					 * Put it to sleep.
Bob Halley's avatar
Bob Halley committed
606 607 608
					 *
					 * XXX detect tasks with 0 references
					 * and do something about them.
Bob Halley's avatar
Bob Halley committed
609
					 */
Bob Halley's avatar
Bob Halley committed
610
					XTRACE("empty");
Bob Halley's avatar
base  
Bob Halley committed
611
					task->state = task_state_idle;
Bob Halley's avatar
Bob Halley committed
612
					done = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
613 614 615 616 617 618 619 620 621 622 623
				} else if (dispatch_count >= task->quantum) {
					/*
					 * Our quantum has expired, but
					 * there is more work to be done.
					 * We'll requeue it to the ready
					 * queue later.
					 *
					 * We don't check quantum until
					 * dispatching at least one event,
					 * so the minimum quantum is one.
					 */
Bob Halley's avatar
Bob Halley committed
624
					XTRACE("quantum");
Bob Halley's avatar
base  
Bob Halley committed
625
					task->state = task_state_ready;
Bob Halley's avatar
Bob Halley committed
626 627
					requeue = ISC_TRUE;
					done = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
628 629 630 631 632
				}
			}
			UNLOCK(&task->lock);

			if (discard_remaining) {
Bob Halley's avatar
Bob Halley committed
633
				isc_event_t next_event;
Bob Halley's avatar
base  
Bob Halley committed
634 635 636 637 638

				for (event = HEAD(remaining_events);
				     event != NULL;
				     event = next_event) {
					next_event = NEXT(event, link);
Bob Halley's avatar
Bob Halley committed
639
					isc_event_free(&event);
Bob Halley's avatar
base  
Bob Halley committed
640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674
				}
			}

			if (free_task)
				task_free(task);

			LOCK(&manager->lock);
			if (requeue) {
				/*
				 * We know we're awake, so we don't have
				 * to wakeup any sleeping threads if the
				 * ready queue is empty before we requeue.
				 *
				 * A possible optimization if the queue is
				 * empty is to 'goto' the 'if (task != NULL)'
				 * block, avoiding the ENQUEUE of the task
				 * and the subsequent immediate DEQUEUE
				 * (since it is the only executable task).
				 * We don't do this because then we'd be
				 * skipping the exit_requested check.  The
				 * cost of ENQUEUE is low anyway, especially
				 * when you consider that we'd have to do
				 * an extra EMPTY check to see if we could
				 * do the optimization.  If the ready queue
				 * were usually nonempty, the 'optimization'
				 * might even hurt rather than help.
				 */
				ENQUEUE(manager->ready_tasks, task,
					ready_link);
			}
		}
	}
	INSIST(manager->workers > 0);
	manager->workers--;
	if (manager->workers == 0)
Bob Halley's avatar
Bob Halley committed
675
		no_workers = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
676 677 678 679 680
	UNLOCK(&manager->lock);

	if (no_workers)
		BROADCAST(&manager->no_workers);

Bob Halley's avatar
Bob Halley committed
681
	XTRACE("exit");
Bob Halley's avatar
base  
Bob Halley committed
682 683 684 685 686

	return (NULL);	
}

static void
Bob Halley's avatar
Bob Halley committed
687
manager_free(isc_taskmgr_t manager) {
Bob Halley's avatar
update  
Bob Halley committed
688 689 690
	(void)os_condition_destroy(&manager->work_available);
	(void)os_condition_destroy(&manager->no_workers);
	(void)os_mutex_destroy(&manager->lock);
Bob Halley's avatar
base  
Bob Halley committed
691
	manager->magic = 0;
Bob Halley's avatar
Bob Halley committed
692
	isc_mem_put(manager->mctx, manager, sizeof *manager);
Bob Halley's avatar
base  
Bob Halley committed
693 694
}

Bob Halley's avatar
Bob Halley committed
695
unsigned int
Bob Halley's avatar
Bob Halley committed
696 697
isc_taskmgr_create(isc_memctx_t mctx, unsigned int workers, 
		   unsigned int default_quantum, isc_taskmgr_t *managerp)
Bob Halley's avatar
Bob Halley committed
698 699
{
	unsigned int i, started = 0;
Bob Halley's avatar
Bob Halley committed
700
	isc_taskmgr_t manager;
Bob Halley's avatar
base  
Bob Halley committed
701 702
	os_thread_t thread;

Bob Halley's avatar
update  
Bob Halley committed
703 704
	if (workers == 0)
		return (0);
Bob Halley's avatar
Bob Halley committed
705
	manager = isc_mem_get(mctx, sizeof *manager);
Bob Halley's avatar
base  
Bob Halley committed
706 707 708 709
	if (manager == NULL)
		return (0);
	manager->magic = TASK_MANAGER_MAGIC;
	manager->mctx = mctx;
Bob Halley's avatar
update  
Bob Halley committed
710
	if (!os_mutex_init(&manager->lock)) {
Bob Halley's avatar
Bob Halley committed
711
		isc_mem_put(mctx, manager, sizeof *manager);
Bob Halley's avatar
update  
Bob Halley committed
712 713
		return (0);
	}
Bob Halley's avatar
base  
Bob Halley committed
714 715 716 717 718
	if (default_quantum == 0)
		default_quantum = DEFAULT_DEFAULT_QUANTUM;
	manager->default_quantum = default_quantum;
	INIT_LIST(manager->tasks);
	INIT_LIST(manager->ready_tasks);
Bob Halley's avatar
update  
Bob Halley committed
719 720
	if (!os_condition_init(&manager->work_available)) {
		(void)os_mutex_destroy(&manager->lock);
Bob Halley's avatar
Bob Halley committed
721
		isc_mem_put(mctx, manager, sizeof *manager);
Bob Halley's avatar
update  
Bob Halley committed
722 723
		return (0);
	}
Bob Halley's avatar
Bob Halley committed
724
	manager->exiting = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
725
	manager->workers = 0;
Bob Halley's avatar
update  
Bob Halley committed
726 727 728
	if (!os_condition_init(&manager->no_workers)) {
		(void)os_condition_destroy(&manager->work_available);
		(void)os_mutex_destroy(&manager->lock);
Bob Halley's avatar
Bob Halley committed
729
		isc_mem_put(mctx, manager, sizeof *manager);
Bob Halley's avatar
update  
Bob Halley committed
730 731
		return (0);
	}
Bob Halley's avatar
base  
Bob Halley committed
732 733 734 735 736 737

	LOCK(&manager->lock);
	/*
	 * Start workers.
	 */
	for (i = 0; i < workers; i++) {
Bob Halley's avatar
Bob Halley committed
738
		if (os_thread_create(run, manager, &thread)) {
Bob Halley's avatar
base  
Bob Halley committed
739 740
			manager->workers++;
			started++;
Bob Halley's avatar
update  
Bob Halley committed
741
			(void)os_thread_detach(thread);
Bob Halley's avatar
base  
Bob Halley committed
742 743 744 745 746 747 748 749 750 751 752 753 754 755
		}
	}
	UNLOCK(&manager->lock);

	if (started == 0) {
		manager_free(manager);
		return (0);
	}		

	*managerp = manager;

	return (started);
}

Bob Halley's avatar
update  
Bob Halley committed
756
void
Bob Halley's avatar
Bob Halley committed
757 758 759
isc_taskmgr_destroy(isc_taskmgr_t *managerp) {
	isc_taskmgr_t manager;
	isc_task_t task;
Bob Halley's avatar
base  
Bob Halley committed
760 761 762 763 764

	REQUIRE(managerp != NULL);
	manager = *managerp;
	REQUIRE(VALID_MANAGER(manager));

Bob Halley's avatar
Bob Halley committed
765
	XTRACE("isc_taskmgr_destroy");
Bob Halley's avatar
base  
Bob Halley committed
766 767 768 769
	/*
	 * Only one non-worker thread may ever call this routine.
	 * If a worker thread wants to initiate shutdown of the
	 * task manager, it should ask some non-worker thread to call
Bob Halley's avatar
Bob Halley committed
770
	 * isc_taskmgr_destroy(), e.g. by signalling a condition variable
Bob Halley's avatar
base  
Bob Halley committed
771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788
	 * that the startup thread is sleeping on.
	 */

	/*
	 * Unlike elsewhere, we're going to hold this lock a long time.
	 * We need to do so, because otherwise the list of tasks could
	 * change while we were traversing it.
	 *
	 * This is also the only function where we will hold both the
	 * task manager lock and a task lock at the same time.
	 */

	LOCK(&manager->lock);

	/*
	 * Make sure we only get called once.
	 */
	INSIST(!manager->exiting);
Bob Halley's avatar
Bob Halley committed
789
	manager->exiting = ISC_TRUE;
Bob Halley's avatar
base  
Bob Halley committed
790 791

	/*
Bob Halley's avatar
update  
Bob Halley committed
792 793
	 * Post the shutdown event to every task (if it hasn't already been
	 * posted).
Bob Halley's avatar
base  
Bob Halley committed
794 795 796 797 798
	 */
	for (task = HEAD(manager->tasks);
	     task != NULL;
	     task = NEXT(task, link)) {
		LOCK(&task->lock);
Bob Halley's avatar
update  
Bob Halley committed
799 800 801 802 803 804 805 806 807 808 809
		if (task->enqueue_allowed) {
			INSIST(task->shutdown_event != NULL);
			ENQUEUE(task->events, task->shutdown_event, link);
			task->shutdown_event = NULL;
			if (task->state == task_state_idle) {
				task->state = task_state_ready;
				ENQUEUE(manager->ready_tasks, task,
					ready_link);
			}
			INSIST(task->state == task_state_ready ||
			       task->state == task_state_running);
Bob Halley's avatar
Bob Halley committed
810
			task->enqueue_allowed = ISC_FALSE;
Bob Halley's avatar
base  
Bob Halley committed
811 812 813 814 815 816 817 818 819 820 821 822 823
		}
		UNLOCK(&task->lock);
	}

	/*
	 * Wake up any sleeping workers.  This ensures we get work done if
	 * there's work left to do, and if there are already no tasks left
	 * it will cause the workers to see manager->exiting.
	 */
	BROADCAST(&manager->work_available);

	/*
	 * Wait for all the worker threads to exit.
Bob Halley's avatar
update  
Bob Halley committed
824 825 826 827 828 829
	 *
	 * XXX  This will become a timed wait.  If all the workers haven't
	 *      died after we've waited the specified interval, we will
	 *	kill the worker threads.  Should we join with the worker
	 *      threads after killing them or just leave them detached and
	 *      hope they go away?
Bob Halley's avatar
base  
Bob Halley committed
830 831 832 833 834 835 836 837 838 839
	 */
	while (manager->workers > 0)
		WAIT(&manager->no_workers, &manager->lock);

	UNLOCK(&manager->lock);

	manager_free(manager);

	*managerp = NULL;
}