sched: Kill unnecessary check in sched_pre_select().
[paraslash.git] / sched.c
1 /*
2 * Copyright (C) 2006-2011 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 #include <sys/time.h>
12
13 #include "para.h"
14 #include "ipc.h"
15 #include "fd.h"
16 #include "list.h"
17 #include "sched.h"
18 #include "string.h"
19 #include "time.h"
20 #include "error.h"
21
22 static struct list_head pre_select_list, post_select_list;
23 static int initialized;
24
25 static struct timeval now_struct;
26 struct timeval *now = &now_struct;
27
28 /*
29 * Remove a task from the scheduler.
30 *
31 * \param t The task to remove.
32 *
33 * If the pre_select pointer of \a t is not \p NULL, it is removed from
34 * the pre_select list of the scheduler. Same goes for \a post_select.
35 */
36 static void unregister_task(struct task *t)
37 {
38 if (!initialized)
39 return;
40 assert(t->error < 0);
41 PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
42 para_strerror(-t->error));
43 if (t->pre_select)
44 list_del(&t->pre_select_node);
45 if (t->post_select)
46 list_del(&t->post_select_node);
47 }
48
49 static void sched_preselect(struct sched *s)
50 {
51 struct task *t, *tmp;
52 list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
53 if (t->pre_select)
54 t->pre_select(s, t);
55 if (t->error < 0)
56 unregister_task(t);
57 }
58 }
59
60 //#define SCHED_DEBUG 1
61 static inline void call_post_select(struct sched *s, struct task *t)
62 {
63 #ifndef SCHED_DEBUG
64 t->post_select(s, t);
65 #else
66 struct timeval t1, t2, diff;
67 unsigned long pst;
68
69 gettimeofday(&t1, NULL);
70 t->post_select(s, t);
71 gettimeofday(&t2, NULL);
72 tv_diff(&t1, &t2, &diff);
73 pst = tv2ms(&diff);
74 if (pst > 50)
75 PARA_WARNING_LOG("%s: post_select time: %lums\n",
76 t->status, pst);
77 #endif
78 }
79
80 static void sched_post_select(struct sched *s)
81 {
82 struct task *t, *tmp;
83
84 list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
85 if (t->error >= 0)
86 call_post_select(s, t);
87 // PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
88 if (t->error >= 0)
89 continue;
90 /*
91 * We have to check whether the list is empty because the call
92 * to ->post_select() might have called sched_shutdown(). In
93 * this case t has been unregistered already, so we must not
94 * unregister it again.
95 */
96 if (list_empty(&post_select_list))
97 return;
98 unregister_task(t);
99 }
100 }
101
102 /**
103 * The core function for all paraslash programs.
104 *
105 * \param s Pointer to the scheduler struct.
106 *
107 * This function updates the global \a now pointer, calls all registered
108 * pre_select hooks which may set the timeout and add any file descriptors to
109 * the fd sets of \a s. Next, it calls para_select() and makes the result available
110 * to the registered tasks by calling their post_select hook.
111 *
112 * \return Zero if no more tasks are left in either of the two lists, negative
113 * if para_select returned an error.
114 *
115 * \sa task, now.
116 */
117 int schedule(struct sched *s)
118 {
119 int ret;
120
121 if (!initialized)
122 return -E_NOT_INITIALIZED;
123 if (!s->select_function)
124 s->select_function = para_select;
125 again:
126 FD_ZERO(&s->rfds);
127 FD_ZERO(&s->wfds);
128 s->select_timeout = s->default_timeout;
129 s->max_fileno = -1;
130 gettimeofday(now, NULL);
131 sched_preselect(s);
132 if (list_empty(&pre_select_list) && list_empty(&post_select_list))
133 return 0;
134 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
135 &s->select_timeout);
136 if (ret < 0)
137 return ret;
138 if (ret == 0) {
139 /*
140 * APUE: Be careful not to check the descriptor sets on return
141 * unless the return value is greater than zero. The return
142 * state of the descriptor sets is implementation dependent if
143 * either a signal is caught or the timer expires.
144 */
145 FD_ZERO(&s->rfds);
146 FD_ZERO(&s->wfds);
147 }
148 gettimeofday(now, NULL);
149 sched_post_select(s);
150 if (list_empty(&pre_select_list) && list_empty(&post_select_list))
151 return 0;
152 goto again;
153 }
154
155 /*
156 * Initialize the paraslash scheduler.
157 */
158 static void init_sched(void)
159 {
160 PARA_INFO_LOG("initializing scheduler\n");
161 INIT_LIST_HEAD(&pre_select_list);
162 INIT_LIST_HEAD(&post_select_list);
163 initialized = 1;
164 }
165
166 /**
167 * Add a task to the scheduler.
168 *
169 * \param t the task to add
170 *
171 * If the pre_select pointer of \a t is not \p NULL, it is added to
172 * the pre_select list of the scheduler. Same goes for post_select.
173 *
174 * \sa task::pre_select, task::post_select
175 */
176 void register_task(struct task *t)
177 {
178 if (!initialized)
179 init_sched();
180 PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
181 if (t->pre_select) {
182 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
183 list_add_tail(&t->pre_select_node, &pre_select_list);
184 }
185 if (t->post_select) {
186 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
187 list_add_tail(&t->post_select_node, &post_select_list);
188 }
189 }
190
191 /**
192 * Unregister all tasks.
193 *
194 * This will cause \a schedule() to return immediately because both the
195 * \a pre_select_list and the \a post_select_list are empty. This function
196 * must be called from the post_select (rather than the pre_select) method.
197 */
198 void sched_shutdown(void)
199 {
200 struct task *t, *tmp;
201
202 if (!initialized)
203 return;
204 list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
205 t->error = -E_SCHED_SHUTDOWN;
206 unregister_task(t);
207 }
208 list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
209 t->error = -E_SCHED_SHUTDOWN;
210 unregister_task(t);
211 }
212 initialized = 0;
213 }
214
215 /**
216 * Get the list of all registered tasks.
217 *
218 * \return The task list.
219 *
220 * Each entry of the list contains an identifier which is simply a hex number.
221 * The result is dynamically allocated and must be freed by the caller.
222 */
223 char *get_task_list(void)
224 {
225 struct task *t, *tmp;
226 char *msg = NULL;
227
228 if (!initialized)
229 return NULL;
230 list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
231 char *tmp_msg;
232 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
233 free(msg);
234 msg = tmp_msg;
235 }
236 list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
237 char *tmp_msg;
238 // if (t->pre_select)
239 // continue;
240 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
241 free(msg);
242 msg = tmp_msg;
243 }
244 //PARA_DEBUG_LOG("task list:\n%s", msg);
245 return msg;
246 }
247
248 /**
249 * Set the select timeout to the minimal possible value.
250 *
251 * \param s Pointer to the scheduler struct.
252 *
253 * This causes the next select() call to return immediately.
254 */
255 void sched_min_delay(struct sched *s)
256 {
257 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
258 }
259
260 /**
261 * Impose an upper bound for the timeout of the next select() call.
262 *
263 * \param to Maximal allowed timeout.
264 * \param s Pointer to the scheduler struct.
265 *
266 * If the current scheduler timeout is already smaller than \a to, this
267 * function does nothing. Otherwise the timeout for the next select() call is
268 * set to the given value.
269 *
270 * \sa sched_request_timeout_ms().
271 */
272 void sched_request_timeout(struct timeval *to, struct sched *s)
273 {
274 if (tv_diff(&s->select_timeout, to, NULL) > 0)
275 s->select_timeout = *to;
276 }
277
278 /**
279 * Force the next select() call to return before the given amount of milliseconds.
280 *
281 * \param ms The maximal allowed timeout in milliseconds.
282 * \param s Pointer to the scheduler struct.
283 *
284 * Like sched_request_timeout() this imposes an upper bound on the timeout
285 * value for the next select() call.
286 */
287 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
288 {
289 struct timeval tv;
290 ms2tv(ms, &tv);
291 sched_request_timeout(&tv, s);
292 }
293
294 /**
295 * Force the next select() call to return before the given future time.
296 *
297 * \param barrier Absolute time before select() should return.
298 * \param s Pointer to the scheduler struct.
299 *
300 * If \a barrier is in the past, this function does nothing.
301 *
302 * \sa sched_request_barrier_or_min_delay().
303 */
304 void sched_request_barrier(struct timeval *barrier, struct sched *s)
305 {
306 struct timeval diff;
307
308 if (tv_diff(now, barrier, &diff) > 0)
309 return;
310 sched_request_timeout(&diff, s);
311 }
312
313 /**
314 * Force the next select() call to return before the given time.
315 *
316 * \param barrier Absolute time before select() should return.
317 * \param s Pointer to the scheduler struct.
318 *
319 * If \a barrier is in the past, this function requests a minimal timeout.
320 *
321 * \sa sched_min_delay(), sched_request_barrier().
322 */
323 void sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
324 {
325 struct timeval diff;
326
327 if (tv_diff(now, barrier, &diff) > 0)
328 return sched_min_delay(s);
329 sched_request_timeout(&diff, s);
330 }