mixer: Trivial whitespace fix.
[paraslash.git] / sched.c
1 /* Copyright (C) 2006 Andre Noll <maan@tuebingen.mpg.de>, see file COPYING. */
2
3 /** \file sched.c Paraslash's scheduling functions. */
4
5 #include <regex.h>
6
7 #include "para.h"
8 #include "ipc.h"
9 #include "fd.h"
10 #include "list.h"
11 #include "sched.h"
12 #include "string.h"
13 #include "time.h"
14 #include "error.h"
15
16 /**
17 * The possible states of a task.
18 *
19 * In addition to the states listed here, a task may also enter zombie state.
20 * This happens when its ->post_select function returns negative, the ->status
21 * field is then set to this return value. Such tasks are not scheduled any
22 * more (i.e. ->pre_select() and ->post_select() are no longer called), but
23 * they stay on the scheduler task list until \ref task_reap() or
24 * \ref sched_shutdown() is called.
25 */
26 enum task_status {
27 /** Task has been reaped and may be removed from the task list. */
28 TS_DEAD,
29 /** Task is active. */
30 TS_RUNNING,
31 };
32
33 struct task {
34 /** A copy of the task name supplied when the task was registered. */
35 char *name;
36 /** Copied during task_register(). */
37 struct task_info info;
38 /* TS_RUNNING, TS_DEAD, or zombie (negative value). */
39 int status;
40 /** Position of the task in the task list of the scheduler. */
41 struct list_head node;
42 /** If less than zero, the task was notified by another task. */
43 int notification;
44 };
45
46 static struct timeval now_struct;
47 const struct timeval *now = &now_struct;
48
49 static void sched_preselect(struct sched *s)
50 {
51 struct task *t, *tmp;
52
53 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
54 if (t->status < 0)
55 continue;
56 if (t->notification != 0)
57 sched_min_delay(s);
58 if (t->info.pre_select)
59 t->info.pre_select(s, t->info.context);
60 }
61 }
62
63 static void unlink_and_free_task(struct task *t)
64 {
65 PARA_INFO_LOG("freeing task %s (%s)\n", t->name, t->status < 0?
66 para_strerror(-t->status) :
67 (t->status == TS_DEAD? "[dead]" : "[running]"));
68
69 list_del(&t->node);
70 free(t->name);
71 free(t);
72 }
73
74 //#define SCHED_DEBUG 1
75 static inline void call_post_select(struct sched *s, struct task *t)
76 {
77 int ret;
78
79 #ifndef SCHED_DEBUG
80 ret = t->info.post_select(s, t->info.context);
81 #else
82 struct timeval t1, t2, diff;
83 unsigned long pst;
84
85 clock_get_realtime(&t1);
86 ret = t->info.post_select(s, t->info.context);
87 clock_get_realtime(&t2);
88 tv_diff(&t1, &t2, &diff);
89 pst = tv2ms(&diff);
90 if (pst > 50)
91 PARA_WARNING_LOG("%s: post_select time: %lums\n",
92 t->name, pst);
93 #endif
94 t->status = ret < 0? ret : TS_RUNNING;
95 }
96
97 static unsigned sched_post_select(struct sched *s)
98 {
99 struct task *t, *tmp;
100 unsigned num_running_tasks = 0;
101
102 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
103 if (t->status == TS_DEAD) /* task has been reaped */
104 unlink_and_free_task(t);
105 else if (t->status == TS_RUNNING) {
106 call_post_select(s, t); /* sets t->status */
107 t->notification = 0;
108 if (t->status == TS_RUNNING)
109 num_running_tasks++;
110 }
111 }
112 return num_running_tasks;
113 }
114
115 /**
116 * The core function of all paraslash programs.
117 *
118 * \param s Pointer to the scheduler struct.
119 *
120 * This function updates the global \a now pointer, calls all registered
121 * pre_select hooks which may set the timeout and add any file descriptors to
122 * the fd sets of \a s. Next, it calls para_select() and makes the result available
123 * to the registered tasks by calling their post_select hook.
124 *
125 * \return Zero if no more tasks are left in the task list, negative if the
126 * select function returned an error.
127 *
128 * \sa \ref now.
129 */
130 int schedule(struct sched *s)
131 {
132 int ret;
133 unsigned num_running_tasks;
134
135 if (!s->select_function)
136 s->select_function = para_select;
137 again:
138 FD_ZERO(&s->rfds);
139 FD_ZERO(&s->wfds);
140 s->select_timeout = s->default_timeout;
141 s->max_fileno = -1;
142 clock_get_realtime(&now_struct);
143 sched_preselect(s);
144 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
145 &s->select_timeout);
146 if (ret < 0)
147 return ret;
148 if (ret == 0) {
149 /*
150 * APUE: Be careful not to check the descriptor sets on return
151 * unless the return value is greater than zero. The return
152 * state of the descriptor sets is implementation dependent if
153 * either a signal is caught or the timer expires.
154 */
155 FD_ZERO(&s->rfds);
156 FD_ZERO(&s->wfds);
157 }
158 clock_get_realtime(&now_struct);
159 num_running_tasks = sched_post_select(s);
160 if (num_running_tasks == 0)
161 return 0;
162 goto again;
163 }
164
165 /**
166 * Obtain the error status of a task and deallocate its resources.
167 *
168 * \param tptr Identifies the task to reap.
169 *
170 * This function is similar to wait(2) in that it returns information about a
171 * terminated task which allows releasing the resources associated with the
172 * task. Until this function is called, the terminated task remains in a zombie
173 * state.
174 *
175 * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
176 * nothing and returns zero. Otherwise, it is checked whether the task
177 * identified by \a tptr is still running. If it is, the function returns zero
178 * and again, no action is taken. Otherwise the (negative) error code of the
179 * terminated task is returned and \a *tptr is set to \p NULL. The task will
180 * then be removed removed from the scheduler task list.
181 *
182 * \sa \ref sched_shutdown(), wait(2).
183 */
184 int task_reap(struct task **tptr)
185 {
186 struct task *t;
187 int ret;
188
189 if (!tptr)
190 return 0;
191 t = *tptr;
192 if (!t)
193 return 0;
194 if (t->status >= 0)
195 return 0;
196 ret = t->status;
197 /*
198 * With list_for_each_entry_safe() it is only safe to remove the
199 * _current_ list item. Since we are being called from the loop in
200 * schedule() via some task's ->post_select() function, freeing the
201 * given task here would result in use-after-free bugs in schedule().
202 * So we only set the task status to TS_DEAD which tells schedule() to
203 * free the task in the next iteration of its loop.
204 */
205 t->status = TS_DEAD;
206
207 *tptr = NULL;
208 return ret;
209 }
210
211 /**
212 * Deallocate all resources of all tasks of a scheduler instance.
213 *
214 * \param s The scheduler instance.
215 *
216 * This should only be called after \ref schedule() has returned.
217 */
218 void sched_shutdown(struct sched *s)
219 {
220 struct task *t, *tmp;
221
222 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
223 if (t->status == TS_RUNNING)
224 /* The task list should contain only terminated tasks. */
225 PARA_WARNING_LOG("shutting down running task %s\n",
226 t->name);
227 unlink_and_free_task(t);
228 }
229 }
230
231 /**
232 * Add a task to the scheduler task list.
233 *
234 * \param info Task information supplied by the caller.
235 * \param s The scheduler instance.
236 *
237 * \return A pointer to a newly allocated task structure. It will be
238 * freed by sched_shutdown().
239 */
240 struct task *task_register(struct task_info *info, struct sched *s)
241 {
242 struct task *t = para_malloc(sizeof(*t));
243
244 assert(info->post_select);
245
246 if (!s->task_list.next)
247 INIT_LIST_HEAD(&s->task_list);
248
249 t->info = *info;
250 t->name = para_strdup(info->name);
251 t->notification = 0;
252 t->status = TS_RUNNING;
253 list_add_tail(&t->node, &s->task_list);
254 return t;
255 }
256
257 /**
258 * Get the list of all registered tasks.
259 *
260 * \param s The scheduler instance to get the task list from.
261 *
262 * \return The task list.
263 *
264 * Each entry of the list contains an identifier which is simply a hex number.
265 * The result is dynamically allocated and must be freed by the caller.
266 */
267 char *get_task_list(struct sched *s)
268 {
269 struct task *t, *tmp;
270 char *msg = NULL;
271
272 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
273 char *tmp_msg;
274 tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
275 t->status == TS_DEAD? "dead" :
276 (t->status == TS_RUNNING? "running" : "zombie"),
277 t->name);
278 free(msg);
279 msg = tmp_msg;
280 }
281 return msg;
282 }
283
284 /**
285 * Set the notification value of a task.
286 *
287 * \param t The task to notify.
288 * \param err A positive error code.
289 *
290 * Tasks which honor notifications are supposed to call \ref
291 * task_get_notification() in their post_select function and act on the
292 * returned notification value.
293 *
294 * If the scheduler detects during its pre_select loop that at least one task
295 * has been notified, the loop terminates, and the post_select methods of all
296 * taks are immediately called again.
297 *
298 * The notification for a task is reset after the call to its post_select
299 * method.
300 *
301 * \sa \ref task_get_notification().
302 */
303 void task_notify(struct task *t, int err)
304 {
305 assert(err > 0);
306 if (t->notification == -err) /* ignore subsequent notifications */
307 return;
308 PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
309 t->notification = -err;
310 }
311
312 /**
313 * Return the notification value of a task.
314 *
315 * \param t The task to get the notification value from.
316 *
317 * \return The notification value. If this is negative, the task has been
318 * notified by another task. Tasks are supposed to check for notifications by
319 * calling this function from their post_select method.
320 *
321 * \sa \ref task_notify().
322 */
323 int task_get_notification(const struct task *t)
324 {
325 return t->notification;
326 }
327
328 /**
329 * Return the status value of a task.
330 *
331 * \param t The task to get the status value from.
332 *
333 * \return Zero if task does not exist, one if task is running, negative error
334 * code if task has terminated.
335 */
336 int task_status(const struct task *t)
337 {
338 if (!t)
339 return 0;
340 if (t->status == TS_DEAD) /* pretend dead tasks don't exist */
341 return 0;
342 if (t->status == TS_RUNNING)
343 return 1;
344 return t->status;
345 }
346
347 /**
348 * Set the notification value of all tasks of a scheduler instance.
349 *
350 * \param s The scheduler instance whose tasks should be notified.
351 * \param err A positive error code.
352 *
353 * This simply iterates over all existing tasks of \a s and sets each
354 * task's notification value to \p -err.
355 */
356 void task_notify_all(struct sched *s, int err)
357 {
358 struct task *t;
359
360 list_for_each_entry(t, &s->task_list, node)
361 task_notify(t, err);
362 }
363
364 /**
365 * Set the select timeout to the minimal possible value.
366 *
367 * \param s Pointer to the scheduler struct.
368 *
369 * This causes the next select() call to return immediately.
370 */
371 void sched_min_delay(struct sched *s)
372 {
373 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
374 }
375
376 /**
377 * Impose an upper bound for the timeout of the next select() call.
378 *
379 * \param to Maximal allowed timeout.
380 * \param s Pointer to the scheduler struct.
381 *
382 * If the current scheduler timeout is already smaller than \a to, this
383 * function does nothing. Otherwise the timeout for the next select() call is
384 * set to the given value.
385 *
386 * \sa \ref sched_request_timeout_ms().
387 */
388 void sched_request_timeout(struct timeval *to, struct sched *s)
389 {
390 if (tv_diff(&s->select_timeout, to, NULL) > 0)
391 s->select_timeout = *to;
392 }
393
394 /**
395 * Force the next select() call to return before the given amount of milliseconds.
396 *
397 * \param ms The maximal allowed timeout in milliseconds.
398 * \param s Pointer to the scheduler struct.
399 *
400 * Like sched_request_timeout() this imposes an upper bound on the timeout
401 * value for the next select() call.
402 */
403 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
404 {
405 struct timeval tv;
406 ms2tv(ms, &tv);
407 sched_request_timeout(&tv, s);
408 }
409
410 /**
411 * Force the next select() call to return before the given future time.
412 *
413 * \param barrier Absolute time before select() should return.
414 * \param s Pointer to the scheduler struct.
415 *
416 * \return If \a barrier is in the past, this function does nothing and returns
417 * zero. Otherwise it returns one.
418 *
419 * \sa \ref sched_request_barrier_or_min_delay().
420 */
421 int sched_request_barrier(struct timeval *barrier, struct sched *s)
422 {
423 struct timeval diff;
424
425 if (tv_diff(now, barrier, &diff) > 0)
426 return 0;
427 sched_request_timeout(&diff, s);
428 return 1;
429 }
430
431 /**
432 * Force the next select() call to return before the given time.
433 *
434 * \param barrier Absolute time before select() should return.
435 * \param s Pointer to the scheduler struct.
436 *
437 * \return If \a barrier is in the past, this function requests a minimal
438 * timeout and returns zero. Otherwise it returns one.
439 *
440 * \sa \ref sched_min_delay(), \ref sched_request_barrier().
441 */
442 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
443 {
444 struct timeval diff;
445
446 if (tv_diff(now, barrier, &diff) > 0) {
447 sched_min_delay(s);
448 return 0;
449 }
450 sched_request_timeout(&diff, s);
451 return 1;
452 }