Remove unnecessary system header includes.
[paraslash.git] / sched.c
1 /*
2 * Copyright (C) 2006-2014 Andre Noll <maan@tuebingen.mpg.de>
3 *
4 * Licensed under the GPL v2. For licencing details see COPYING.
5 */
6
7 /** \file sched.c Paraslash's scheduling functions. */
8
9 #include <regex.h>
10
11 #include "para.h"
12 #include "ipc.h"
13 #include "fd.h"
14 #include "list.h"
15 #include "sched.h"
16 #include "string.h"
17 #include "time.h"
18 #include "error.h"
19
20 /**
21 * The possible states of a task.
22 *
23 * In addition to the states listed here, a task may also enter zombie state.
24 * This happens when its ->post_select function returns negative, the ->status
25 * field is then set to this return value. Such tasks are not scheduled any
26 * more (i.e. ->pre_select() and ->post_select() are no longer called), but
27 * they stay on the scheduler task list until \ref task_reap() or
28 * \ref sched_shutdown() is called.
29 */
30 enum task_status {
31 /** Task has been reaped and may be removed from the task list. */
32 TS_DEAD,
33 /** Task is active. */
34 TS_RUNNING,
35 };
36
37 struct task {
38 /** A copy of the task name supplied when the task was registered. */
39 char *name;
40 /** Copied during task_register(). */
41 struct task_info info;
42 /* TS_RUNNING, TS_DEAD, or zombie (negative value). */
43 int status;
44 /** Position of the task in the task list of the scheduler. */
45 struct list_head node;
46 /** If less than zero, the task was notified by another task. */
47 int notification;
48 };
49
50 static struct timeval now_struct;
51 const struct timeval *now = &now_struct;
52
53 static inline bool timeout_is_zero(struct sched *s)
54 {
55 struct timeval *tv = &s->select_timeout;
56 return tv->tv_sec == 0 && tv->tv_usec == 0;
57 }
58
59 static void sched_preselect(struct sched *s)
60 {
61 struct task *t, *tmp;
62
63 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
64 if (t->status < 0)
65 continue;
66 if (t->notification != 0)
67 sched_min_delay(s);
68 if (t->info.pre_select)
69 t->info.pre_select(s, t->info.context);
70 }
71 }
72
73 static void unlink_and_free_task(struct task *t)
74 {
75 PARA_INFO_LOG("freeing task %s\n", t->name);
76 list_del(&t->node);
77 free(t->name);
78 free(t);
79 }
80
81 //#define SCHED_DEBUG 1
82 static inline void call_post_select(struct sched *s, struct task *t)
83 {
84 int ret;
85
86 #ifndef SCHED_DEBUG
87 ret = t->info.post_select(s, t->info.context);
88 #else
89 struct timeval t1, t2, diff;
90 unsigned long pst;
91
92 clock_get_realtime(&t1);
93 ret = t->info.post_select(s, t->info.context);
94 clock_get_realtime(&t2);
95 tv_diff(&t1, &t2, &diff);
96 pst = tv2ms(&diff);
97 if (pst > 50)
98 PARA_WARNING_LOG("%s: post_select time: %lums\n",
99 t->name, pst);
100 #endif
101 t->status = ret < 0? ret : TS_RUNNING;
102 }
103
104 static unsigned sched_post_select(struct sched *s)
105 {
106 struct task *t, *tmp;
107 unsigned num_running_tasks = 0;
108
109 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
110 if (t->status == TS_DEAD) /* task has been reaped */
111 unlink_and_free_task(t);
112 else if (t->status == TS_RUNNING) {
113 call_post_select(s, t); /* sets t->status */
114 t->notification = 0;
115 if (t->status == TS_RUNNING)
116 num_running_tasks++;
117 }
118 }
119 return num_running_tasks;
120 }
121
122 /**
123 * The core function of all paraslash programs.
124 *
125 * \param s Pointer to the scheduler struct.
126 *
127 * This function updates the global \a now pointer, calls all registered
128 * pre_select hooks which may set the timeout and add any file descriptors to
129 * the fd sets of \a s. Next, it calls para_select() and makes the result available
130 * to the registered tasks by calling their post_select hook.
131 *
132 * \return Zero if no more tasks are left in the task list, negative if the
133 * select function returned an error.
134 *
135 * \sa \ref now.
136 */
137 int schedule(struct sched *s)
138 {
139 int ret;
140 unsigned num_running_tasks;
141
142 if (!s->select_function)
143 s->select_function = para_select;
144 again:
145 FD_ZERO(&s->rfds);
146 FD_ZERO(&s->wfds);
147 s->select_timeout = s->default_timeout;
148 s->max_fileno = -1;
149 clock_get_realtime(&now_struct);
150 sched_preselect(s);
151 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
152 &s->select_timeout);
153 if (ret < 0)
154 return ret;
155 if (ret == 0) {
156 /*
157 * APUE: Be careful not to check the descriptor sets on return
158 * unless the return value is greater than zero. The return
159 * state of the descriptor sets is implementation dependent if
160 * either a signal is caught or the timer expires.
161 */
162 FD_ZERO(&s->rfds);
163 FD_ZERO(&s->wfds);
164 }
165 clock_get_realtime(&now_struct);
166 num_running_tasks = sched_post_select(s);
167 if (num_running_tasks == 0)
168 return 0;
169 goto again;
170 }
171
172 /**
173 * Obtain the error status of a task and deallocate its resources.
174 *
175 * \param tptr Identifies the task to reap.
176 *
177 * This function is similar to wait(2) in that it returns information about a
178 * terminated task and allows to release the resources associated with the
179 * task. Until this function is called, the terminated task remains in a zombie
180 * state.
181 *
182 * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
183 * nothing and returns zero. Otherwise, it is checked whether the task
184 * identified by \a tptr is still running. If it is, the function returns zero
185 * and again, no action is taken. Otherwise the (negative) error code of the
186 * terminated task is returned and \a *tptr is set to \p NULL. The task will
187 * then be removed removed from the scheduler task list.
188 *
189 * \sa \ref sched_shutdown(), wait(2).
190 */
191 int task_reap(struct task **tptr)
192 {
193 struct task *t;
194 int ret;
195
196 if (!tptr)
197 return 0;
198 t = *tptr;
199 if (!t)
200 return 0;
201 if (t->status >= 0)
202 return 0;
203 ret = t->status;
204 /*
205 * With list_for_each_entry_safe() it is only safe to remove the
206 * _current_ list item. Since we are being called from the loop in
207 * schedule() via some task's ->post_select() function, freeing the
208 * given task here would result in use-after-free bugs in schedule().
209 * So we only set the task status to TS_DEAD which tells schedule() to
210 * free the task in the next iteration of its loop.
211 */
212 t->status = TS_DEAD;
213
214 *tptr = NULL;
215 return ret;
216 }
217
218 /**
219 * Deallocate all resources of all tasks of a scheduler instance.
220 *
221 * \param s The scheduler instance.
222 *
223 * This should only be called after \ref schedule() has returned.
224 */
225 void sched_shutdown(struct sched *s)
226 {
227 struct task *t, *tmp;
228
229 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
230 if (t->status == TS_RUNNING)
231 /* The task list should contain only terminated tasks. */
232 PARA_WARNING_LOG("shutting down running task %s\n",
233 t->name);
234 unlink_and_free_task(t);
235 }
236 }
237
238 /**
239 * Add a task to the scheduler task list.
240 *
241 * \param info Task information supplied by the caller.
242 * \param s The scheduler instance.
243 *
244 * \return A pointer to a newly allocated task structure. It will be
245 * freed by sched_shutdown().
246 */
247 struct task *task_register(struct task_info *info, struct sched *s)
248 {
249 struct task *t = para_malloc(sizeof(*t));
250
251 assert(info->post_select);
252
253 if (!s->task_list.next)
254 INIT_LIST_HEAD(&s->task_list);
255
256 t->info = *info;
257 t->name = para_strdup(info->name);
258 t->notification = 0;
259 t->status = TS_RUNNING;
260 list_add_tail(&t->node, &s->task_list);
261 return t;
262 }
263
264 /**
265 * Get the list of all registered tasks.
266 *
267 * \param s The scheduler instance to get the task list from.
268 *
269 * \return The task list.
270 *
271 * Each entry of the list contains an identifier which is simply a hex number.
272 * The result is dynamically allocated and must be freed by the caller.
273 */
274 char *get_task_list(struct sched *s)
275 {
276 struct task *t, *tmp;
277 char *msg = NULL;
278
279 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
280 char *tmp_msg;
281 tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
282 t->status == TS_DEAD? "dead" :
283 (t->status == TS_RUNNING? "running" : "zombie"),
284 t->name);
285 free(msg);
286 msg = tmp_msg;
287 }
288 return msg;
289 }
290
291 /**
292 * Set the notification value of a task.
293 *
294 * \param t The task to notify.
295 * \param err A positive error code.
296 *
297 * Tasks which honor notifications are supposed to call \ref
298 * task_get_notification() in their post_select function and act on the
299 * returned notification value.
300 *
301 * If the scheduler detects during its pre_select loop that at least one task
302 * has been notified, the loop terminates, and the post_select methods of all
303 * taks are immediately called again.
304 *
305 * The notification for a task is reset after the call to its post_select
306 * method.
307 *
308 * \sa \ref task_get_notification().
309 */
310 void task_notify(struct task *t, int err)
311 {
312 assert(err > 0);
313 if (t->notification == -err) /* ignore subsequent notifications */
314 return;
315 PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
316 t->notification = -err;
317 }
318
319 /**
320 * Return the notification value of a task.
321 *
322 * \param t The task to get the notification value from.
323 *
324 * \return The notification value. If this is negative, the task has been
325 * notified by another task. Tasks are supposed to check for notifications by
326 * calling this function from their post_select method.
327 *
328 * \sa \ref task_notify().
329 */
330 int task_get_notification(const struct task *t)
331 {
332 return t->notification;
333 }
334
335 /**
336 * Return the status value of a task.
337 *
338 * \param t The task to get the status value from.
339 *
340 * \return Zero if task does not exist, one if task is running, negative error
341 * code if task has terminated.
342 */
343 int task_status(const struct task *t)
344 {
345 if (!t)
346 return 0;
347 if (t->status == TS_DEAD) /* pretend dead tasks don't exist */
348 return 0;
349 if (t->status == TS_RUNNING)
350 return 1;
351 return t->status;
352 }
353
354 /**
355 * Set the notification value of all tasks of a scheduler instance.
356 *
357 * \param s The scheduler instance whose tasks should be notified.
358 * \param err A positive error code.
359 *
360 * This simply iterates over all existing tasks of \a s and sets each
361 * task's notification value to \p -err.
362 */
363 void task_notify_all(struct sched *s, int err)
364 {
365 struct task *t;
366
367 list_for_each_entry(t, &s->task_list, node)
368 task_notify(t, err);
369 }
370
371 /**
372 * Set the select timeout to the minimal possible value.
373 *
374 * \param s Pointer to the scheduler struct.
375 *
376 * This causes the next select() call to return immediately.
377 */
378 void sched_min_delay(struct sched *s)
379 {
380 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
381 }
382
383 /**
384 * Impose an upper bound for the timeout of the next select() call.
385 *
386 * \param to Maximal allowed timeout.
387 * \param s Pointer to the scheduler struct.
388 *
389 * If the current scheduler timeout is already smaller than \a to, this
390 * function does nothing. Otherwise the timeout for the next select() call is
391 * set to the given value.
392 *
393 * \sa sched_request_timeout_ms().
394 */
395 void sched_request_timeout(struct timeval *to, struct sched *s)
396 {
397 if (tv_diff(&s->select_timeout, to, NULL) > 0)
398 s->select_timeout = *to;
399 }
400
401 /**
402 * Force the next select() call to return before the given amount of milliseconds.
403 *
404 * \param ms The maximal allowed timeout in milliseconds.
405 * \param s Pointer to the scheduler struct.
406 *
407 * Like sched_request_timeout() this imposes an upper bound on the timeout
408 * value for the next select() call.
409 */
410 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
411 {
412 struct timeval tv;
413 ms2tv(ms, &tv);
414 sched_request_timeout(&tv, s);
415 }
416
417 /**
418 * Force the next select() call to return before the given future time.
419 *
420 * \param barrier Absolute time before select() should return.
421 * \param s Pointer to the scheduler struct.
422 *
423 * \return If \a barrier is in the past, this function does nothing and returns
424 * zero. Otherwise it returns one.
425 *
426 * \sa sched_request_barrier_or_min_delay().
427 */
428 int sched_request_barrier(struct timeval *barrier, struct sched *s)
429 {
430 struct timeval diff;
431
432 if (tv_diff(now, barrier, &diff) > 0)
433 return 0;
434 sched_request_timeout(&diff, s);
435 return 1;
436 }
437
438 /**
439 * Force the next select() call to return before the given time.
440 *
441 * \param barrier Absolute time before select() should return.
442 * \param s Pointer to the scheduler struct.
443 *
444 * \return If \a barrier is in the past, this function requests a minimal
445 * timeout and returns zero. Otherwise it returns one.
446 *
447 * \sa sched_min_delay(), sched_request_barrier().
448 */
449 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
450 {
451 struct timeval diff;
452
453 if (tv_diff(now, barrier, &diff) > 0) {
454 sched_min_delay(s);
455 return 0;
456 }
457 sched_request_timeout(&diff, s);
458 return 1;
459 }