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