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