sched: Provide alternative post_select variant.
[paraslash.git] / sched.c
1 /*
2 * Copyright (C) 2006-2013 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 /*
25 * Remove a task from the scheduler.
26 *
27 * \param t The task to remove.
28 *
29 * If the pre_select pointer of \a t is not \p NULL, it is removed from
30 * the pre_select list of the scheduler. Same goes for \a post_select.
31 */
32 static void unregister_task(struct task *t)
33 {
34 assert(t->error < 0);
35 PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
36 para_strerror(-t->error));
37 if (t->pre_select)
38 list_del(&t->pre_select_node);
39 if (t->new_post_select || t->post_select)
40 list_del(&t->post_select_node);
41 }
42
43 static inline bool timeout_is_zero(struct sched *s)
44 {
45 struct timeval *tv = &s->select_timeout;
46 return tv->tv_sec == 0 && tv->tv_usec == 0;
47 }
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->pre_select_list, pre_select_node) {
54 if (t->notification != 0)
55 sched_min_delay(s);
56 if (t->pre_select)
57 t->pre_select(s, t);
58 }
59 }
60
61 //#define SCHED_DEBUG 1
62 static inline void call_post_select(struct sched *s, struct task *t)
63 {
64 #ifndef SCHED_DEBUG
65 if (t->new_post_select) {
66 t->error = t->new_post_select(s, t);
67 return;
68 }
69 return t->post_select(s, t);
70 #else
71 struct timeval t1, t2, diff;
72 unsigned long pst;
73
74 clock_get_realtime(&t1);
75 if (t->new_post_select)
76 t->error = t->new_post_select(s, t);
77 else
78 t->post_select(s, t);
79 clock_get_realtime(&t2);
80 tv_diff(&t1, &t2, &diff);
81 pst = tv2ms(&diff);
82 if (pst > 50)
83 PARA_WARNING_LOG("%s: post_select time: %lums\n",
84 t->status, pst);
85 #endif
86 }
87
88 static void sched_post_select(struct sched *s)
89 {
90 struct task *t, *tmp;
91
92 list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
93 if (t->error >= 0)
94 call_post_select(s, t);
95 // PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
96 t->notification = 0;
97 if (t->error >= 0)
98 continue;
99 unregister_task(t);
100 }
101 }
102
103 /**
104 * The core function for all paraslash programs.
105 *
106 * \param s Pointer to the scheduler struct.
107 *
108 * This function updates the global \a now pointer, calls all registered
109 * pre_select hooks which may set the timeout and add any file descriptors to
110 * the fd sets of \a s. Next, it calls para_select() and makes the result available
111 * to the registered tasks by calling their post_select hook.
112 *
113 * \return Zero if no more tasks are left in either of the two lists, negative
114 * if para_select returned an error.
115 *
116 * \sa task, now.
117 */
118 int schedule(struct sched *s)
119 {
120 int ret;
121
122 if (!s->select_function)
123 s->select_function = para_select;
124 again:
125 FD_ZERO(&s->rfds);
126 FD_ZERO(&s->wfds);
127 s->select_timeout = s->default_timeout;
128 s->max_fileno = -1;
129 clock_get_realtime(now);
130 sched_preselect(s);
131 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
132 &s->select_timeout);
133 if (ret < 0)
134 return ret;
135 if (ret == 0) {
136 /*
137 * APUE: Be careful not to check the descriptor sets on return
138 * unless the return value is greater than zero. The return
139 * state of the descriptor sets is implementation dependent if
140 * either a signal is caught or the timer expires.
141 */
142 FD_ZERO(&s->rfds);
143 FD_ZERO(&s->wfds);
144 }
145 clock_get_realtime(now);
146 sched_post_select(s);
147 if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
148 return 0;
149 goto again;
150 }
151
152 /**
153 * Add a task to the scheduler.
154 *
155 * \param t The task to add.
156 * \param s The scheduler instance to add the task to.
157 *
158 * If the pre_select pointer of \a t is not \p NULL, it is added to
159 * the pre_select list of the scheduler. Same goes for post_select.
160 *
161 * \sa task::pre_select, task::post_select
162 */
163 void register_task(struct sched *s, struct task *t)
164 {
165 PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
166 t->notification = 0;
167 if (!s->pre_select_list.next)
168 INIT_LIST_HEAD(&s->pre_select_list);
169 if (!s->post_select_list.next)
170 INIT_LIST_HEAD(&s->post_select_list);
171 if (t->pre_select) {
172 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
173 list_add_tail(&t->pre_select_node, &s->pre_select_list);
174 }
175 if (t->new_post_select) {
176 PARA_DEBUG_LOG("post_select: %p\n", &t->new_post_select);
177 list_add_tail(&t->post_select_node, &s->post_select_list);
178 } else if ((t->post_select)) {
179 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
180 list_add_tail(&t->post_select_node, &s->post_select_list);
181 }
182 }
183
184 /**
185 * Get the list of all registered tasks.
186 *
187 * \param s The scheduler instance to get the task list from.
188 *
189 * \return The task list.
190 *
191 * Each entry of the list contains an identifier which is simply a hex number.
192 * The result is dynamically allocated and must be freed by the caller.
193 */
194 char *get_task_list(struct sched *s)
195 {
196 struct task *t, *tmp;
197 char *msg = NULL;
198
199 list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
200 char *tmp_msg;
201 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
202 free(msg);
203 msg = tmp_msg;
204 }
205 list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
206 char *tmp_msg;
207 // if (t->pre_select)
208 // continue;
209 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
210 free(msg);
211 msg = tmp_msg;
212 }
213 //PARA_DEBUG_LOG("task list:\n%s", msg);
214 return msg;
215 }
216
217 /**
218 * Set the notification value of a task.
219 *
220 * \param t The task to notify.
221 * \param err A positive error code.
222 *
223 * Tasks which honor notifications are supposed to call \ref
224 * task_get_notification() in their post_select function and act on the
225 * returned notification value.
226 *
227 * If the scheduler detects during its pre_select loop that at least one task
228 * has been notified, the loop terminates, and the post_select methods of all
229 * taks are immediately called again.
230 *
231 * The notification for a task is reset after the call to its post_select
232 * method.
233 *
234 * \sa \ref task_get_notification().
235 */
236 void task_notify(struct task *t, int err)
237 {
238 assert(err > 0);
239 if (t->notification == -err) /* ignore subsequent notifications */
240 return;
241 PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
242 t->notification = -err;
243 }
244
245 /**
246 * Return the notification value of a task.
247 *
248 * \param t The task to get the notification value from.
249 *
250 * \return The notification value. If this is negative, the task has been
251 * notified by another task. Tasks are supposed to check for notifications by
252 * calling this function from their post_select method.
253 *
254 * \sa \ref task_notify().
255 */
256 int task_get_notification(struct task *t)
257 {
258 return t->notification;
259 }
260
261 /**
262 * Set the notification value of all tasks of a scheduler instance.
263 *
264 * \param s The scheduler instance whose tasks should be notified.
265 * \param err A positive error code.
266 *
267 * This simply iterates over all existing tasks of \a s and sets each
268 * task's notification value to \p -err.
269 */
270 void task_notify_all(struct sched *s, int err)
271 {
272 struct task *t;
273
274 list_for_each_entry(t, &s->pre_select_list, pre_select_node)
275 task_notify(t, err);
276 list_for_each_entry(t, &s->post_select_list, post_select_node)
277 task_notify(t, err);
278 }
279
280 /**
281 * Set the select timeout to the minimal possible value.
282 *
283 * \param s Pointer to the scheduler struct.
284 *
285 * This causes the next select() call to return immediately.
286 */
287 void sched_min_delay(struct sched *s)
288 {
289 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
290 }
291
292 /**
293 * Impose an upper bound for the timeout of the next select() call.
294 *
295 * \param to Maximal allowed timeout.
296 * \param s Pointer to the scheduler struct.
297 *
298 * If the current scheduler timeout is already smaller than \a to, this
299 * function does nothing. Otherwise the timeout for the next select() call is
300 * set to the given value.
301 *
302 * \sa sched_request_timeout_ms().
303 */
304 void sched_request_timeout(struct timeval *to, struct sched *s)
305 {
306 if (tv_diff(&s->select_timeout, to, NULL) > 0)
307 s->select_timeout = *to;
308 }
309
310 /**
311 * Force the next select() call to return before the given amount of milliseconds.
312 *
313 * \param ms The maximal allowed timeout in milliseconds.
314 * \param s Pointer to the scheduler struct.
315 *
316 * Like sched_request_timeout() this imposes an upper bound on the timeout
317 * value for the next select() call.
318 */
319 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
320 {
321 struct timeval tv;
322 ms2tv(ms, &tv);
323 sched_request_timeout(&tv, s);
324 }
325
326 /**
327 * Force the next select() call to return before the given future time.
328 *
329 * \param barrier Absolute time before select() should return.
330 * \param s Pointer to the scheduler struct.
331 *
332 * \return If \a barrier is in the past, this function does nothing and returns
333 * zero. Otherwise it returns one.
334 *
335 * \sa sched_request_barrier_or_min_delay().
336 */
337 int sched_request_barrier(struct timeval *barrier, struct sched *s)
338 {
339 struct timeval diff;
340
341 if (tv_diff(now, barrier, &diff) > 0)
342 return 0;
343 sched_request_timeout(&diff, s);
344 return 1;
345 }
346
347 /**
348 * Force the next select() call to return before the given time.
349 *
350 * \param barrier Absolute time before select() should return.
351 * \param s Pointer to the scheduler struct.
352 *
353 * \return If \a barrier is in the past, this function requests a minimal
354 * timeout and returns zero. Otherwise it returns one.
355 *
356 * \sa sched_min_delay(), sched_request_barrier().
357 */
358 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
359 {
360 struct timeval diff;
361
362 if (tv_diff(now, barrier, &diff) > 0) {
363 sched_min_delay(s);
364 return 0;
365 }
366 sched_request_timeout(&diff, s);
367 return 1;
368 }