sched: Dont use fixed-size buffer for task names.
[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 /** The task name supplied when the task was registered(). */
23 char *name;
24 /** Copied from the task_info struct during task_register(). */
25 void (*pre_select)(struct sched *s, struct task *t);
26 /** Copied from the task_info struct during task_register(). */
27 int (*post_select)(struct sched *s, struct task *t);
28 /** Whether this task is active (>=0) or in error state (<0). */
29 int status;
30 /** Position of the task in the task list of the scheduler. */
31 struct list_head node;
32 /** If less than zero, the task was notified by another task. */
33 int notification;
34 /** True if task is in error state and exit status has been queried. */
35 bool dead;
36 /** Usually a pointer to the struct containing this task. */
37 void *context;
38 };
39
40 static struct timeval now_struct;
41 struct timeval *now = &now_struct;
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->task_list, node) {
54 if (t->status < 0)
55 continue;
56 if (t->notification != 0)
57 sched_min_delay(s);
58 if (t->pre_select)
59 t->pre_select(s, t);
60 }
61 }
62
63 static void unlink_and_free_task(struct task *t)
64 {
65 PARA_INFO_LOG("freeing task %s\n", t->name);
66 list_del(&t->node);
67 free(t->name);
68 free(t);
69 }
70
71 //#define SCHED_DEBUG 1
72 static inline void call_post_select(struct sched *s, struct task *t)
73 {
74 #ifndef SCHED_DEBUG
75 t->status = t->post_select(s, t);
76 #else
77 struct timeval t1, t2, diff;
78 unsigned long pst;
79
80 clock_get_realtime(&t1);
81 t->status = t->post_select(s, t);
82 clock_get_realtime(&t2);
83 tv_diff(&t1, &t2, &diff);
84 pst = tv2ms(&diff);
85 if (pst > 50)
86 PARA_WARNING_LOG("%s: post_select time: %lums\n",
87 t->name, pst);
88 #endif
89 }
90
91 static unsigned sched_post_select(struct sched *s)
92 {
93 struct task *t, *tmp;
94 unsigned num_running_tasks = 0;
95
96 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
97 if (t->status < 0) {
98 if (t->dead) /* task has been reaped */
99 unlink_and_free_task(t);
100 continue;
101 }
102 call_post_select(s, t);
103 t->notification = 0;
104 if (t->status >= 0)
105 num_running_tasks++;
106 }
107 return num_running_tasks;
108 }
109
110 /**
111 * The core function of all paraslash programs.
112 *
113 * \param s Pointer to the scheduler struct.
114 *
115 * This function updates the global \a now pointer, calls all registered
116 * pre_select hooks which may set the timeout and add any file descriptors to
117 * the fd sets of \a s. Next, it calls para_select() and makes the result available
118 * to the registered tasks by calling their post_select hook.
119 *
120 * \return Zero if no more tasks are left in the task list, negative if the
121 * select function returned an error.
122 *
123 * \sa \ref task, \ref now.
124 */
125 int schedule(struct sched *s)
126 {
127 int ret;
128 unsigned num_running_tasks;
129
130 if (!s->select_function)
131 s->select_function = para_select;
132 again:
133 FD_ZERO(&s->rfds);
134 FD_ZERO(&s->wfds);
135 s->select_timeout = s->default_timeout;
136 s->max_fileno = -1;
137 clock_get_realtime(now);
138 sched_preselect(s);
139 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
140 &s->select_timeout);
141 if (ret < 0)
142 return ret;
143 if (ret == 0) {
144 /*
145 * APUE: Be careful not to check the descriptor sets on return
146 * unless the return value is greater than zero. The return
147 * state of the descriptor sets is implementation dependent if
148 * either a signal is caught or the timer expires.
149 */
150 FD_ZERO(&s->rfds);
151 FD_ZERO(&s->wfds);
152 }
153 clock_get_realtime(now);
154 num_running_tasks = sched_post_select(s);
155 if (num_running_tasks == 0)
156 return 0;
157 goto again;
158 }
159
160 /**
161 * Obtain the error status of a task and deallocate its resources.
162 *
163 * \param tptr Identifies the task to reap.
164 *
165 * This function is similar to wait(2) in that it returns information about a
166 * terminated task and allows to release the resources associated with the
167 * task. Until this function is called, the terminated task remains in a zombie
168 * state.
169 *
170 * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
171 * nothing and returns zero. Otherwise, it is checked whether the task
172 * identified by \a tptr is still running. If it is, the function returns zero
173 * and again, no action is taken. Otherwise the (negative) error code of the
174 * terminated task is returned and \a *tptr is set to \p NULL. The task will
175 * then be removed removed from the scheduler task list.
176 *
177 * \sa \ref sched_shutdown(), wait(2).
178 */
179 int task_reap(struct task **tptr)
180 {
181 struct task *t;
182
183 if (!tptr)
184 return 0;
185 t = *tptr;
186 if (!t)
187 return 0;
188 if (t->status >= 0)
189 return 0;
190 if (t->dead) /* will be freed in sched_post_select() */
191 return 0;
192 /*
193 * With list_for_each_entry_safe() it is only safe to remove the
194 * _current_ list item. Since we are being called from the loop in
195 * schedule() via some task's ->post_select() function, freeing the
196 * given task here would result in use-after-free bugs in schedule().
197 * So we only set t->dead which tells schedule() to free the task in
198 * the next iteration of its loop.
199 */
200 t->dead = true;
201 *tptr = NULL;
202 return t->status;
203 }
204
205 /**
206 * Deallocate all resources of all tasks of a scheduler instance.
207 *
208 * \param s The scheduler instance.
209 *
210 * This should only be called after \ref schedule() has returned.
211 */
212 void sched_shutdown(struct sched *s)
213 {
214 struct task *t, *tmp;
215
216 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
217 if (t->status >= 0)
218 /* The task list should contain only terminated tasks. */
219 PARA_WARNING_LOG("shutting down running task %s\n",
220 t->name);
221 unlink_and_free_task(t);
222 }
223 }
224
225 /**
226 * Add a task to the scheduler task list.
227 *
228 * \param info Task information supplied by the caller.
229 * \param s The scheduler instance.
230 *
231 * \return A pointer to a newly allocated task structure. It will be
232 * freed by sched_shutdown().
233 */
234 struct task *task_register(struct task_info *info, struct sched *s)
235 {
236 struct task *t = para_malloc(sizeof(*t));
237
238 assert(info->post_select);
239
240 if (!s->task_list.next)
241 INIT_LIST_HEAD(&s->task_list);
242
243 t->name = para_strdup(info->name);
244 t->notification = 0;
245 t->status = 0;
246 t->dead = false;
247 t->pre_select = info->pre_select;
248 t->post_select = info->post_select;
249 t->context = info->context;
250 list_add_tail(&t->node, &s->task_list);
251 return t;
252 }
253
254 /**
255 * Obtain the context pointer of a task.
256 *
257 * \param t Return this task's context pointer.
258 *
259 * \return A pointer to the memory location specified previously as \a
260 * task_info->context when the task was registered with \ref task_register().
261 */
262 void *task_context(struct task *t)
263 {
264 return t->context;
265 }
266
267 /**
268 * Get the list of all registered tasks.
269 *
270 * \param s The scheduler instance to get the task list from.
271 *
272 * \return The task list.
273 *
274 * Each entry of the list contains an identifier which is simply a hex number.
275 * The result is dynamically allocated and must be freed by the caller.
276 */
277 char *get_task_list(struct sched *s)
278 {
279 struct task *t, *tmp;
280 char *msg = NULL;
281
282 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
283 char *tmp_msg;
284 tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
285 t->status < 0? (t->dead? "dead" : "zombie") : "running",
286 t->name);
287 free(msg);
288 msg = tmp_msg;
289 }
290 return msg;
291 }
292
293 /**
294 * Set the notification value of a task.
295 *
296 * \param t The task to notify.
297 * \param err A positive error code.
298 *
299 * Tasks which honor notifications are supposed to call \ref
300 * task_get_notification() in their post_select function and act on the
301 * returned notification value.
302 *
303 * If the scheduler detects during its pre_select loop that at least one task
304 * has been notified, the loop terminates, and the post_select methods of all
305 * taks are immediately called again.
306 *
307 * The notification for a task is reset after the call to its post_select
308 * method.
309 *
310 * \sa \ref task_get_notification().
311 */
312 void task_notify(struct task *t, int err)
313 {
314 assert(err > 0);
315 if (t->notification == -err) /* ignore subsequent notifications */
316 return;
317 PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
318 t->notification = -err;
319 }
320
321 /**
322 * Return the notification value of a task.
323 *
324 * \param t The task to get the notification value from.
325 *
326 * \return The notification value. If this is negative, the task has been
327 * notified by another task. Tasks are supposed to check for notifications by
328 * calling this function from their post_select method.
329 *
330 * \sa \ref task_notify().
331 */
332 int task_get_notification(const struct task *t)
333 {
334 return t->notification;
335 }
336
337 /**
338 * Return the status value of a task.
339 *
340 * \param t The task to get the status value from.
341 *
342 * \return Zero if task does not exist, one if task is running, negative error
343 * code if task has terminated.
344 */
345 int task_status(const struct task *t)
346 {
347 if (!t)
348 return 0;
349 if (t->dead)
350 return 0;
351 if (t->status >= 0)
352 return 1;
353 return t->status;
354 }
355
356 /**
357 * Set the notification value of all tasks of a scheduler instance.
358 *
359 * \param s The scheduler instance whose tasks should be notified.
360 * \param err A positive error code.
361 *
362 * This simply iterates over all existing tasks of \a s and sets each
363 * task's notification value to \p -err.
364 */
365 void task_notify_all(struct sched *s, int err)
366 {
367 struct task *t;
368
369 list_for_each_entry(t, &s->task_list, node)
370 task_notify(t, err);
371 }
372
373 /**
374 * Set the select timeout to the minimal possible value.
375 *
376 * \param s Pointer to the scheduler struct.
377 *
378 * This causes the next select() call to return immediately.
379 */
380 void sched_min_delay(struct sched *s)
381 {
382 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
383 }
384
385 /**
386 * Impose an upper bound for the timeout of the next select() call.
387 *
388 * \param to Maximal allowed timeout.
389 * \param s Pointer to the scheduler struct.
390 *
391 * If the current scheduler timeout is already smaller than \a to, this
392 * function does nothing. Otherwise the timeout for the next select() call is
393 * set to the given value.
394 *
395 * \sa sched_request_timeout_ms().
396 */
397 void sched_request_timeout(struct timeval *to, struct sched *s)
398 {
399 if (tv_diff(&s->select_timeout, to, NULL) > 0)
400 s->select_timeout = *to;
401 }
402
403 /**
404 * Force the next select() call to return before the given amount of milliseconds.
405 *
406 * \param ms The maximal allowed timeout in milliseconds.
407 * \param s Pointer to the scheduler struct.
408 *
409 * Like sched_request_timeout() this imposes an upper bound on the timeout
410 * value for the next select() call.
411 */
412 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
413 {
414 struct timeval tv;
415 ms2tv(ms, &tv);
416 sched_request_timeout(&tv, s);
417 }
418
419 /**
420 * Force the next select() call to return before the given future time.
421 *
422 * \param barrier Absolute time before select() should return.
423 * \param s Pointer to the scheduler struct.
424 *
425 * \return If \a barrier is in the past, this function does nothing and returns
426 * zero. Otherwise it returns one.
427 *
428 * \sa sched_request_barrier_or_min_delay().
429 */
430 int sched_request_barrier(struct timeval *barrier, struct sched *s)
431 {
432 struct timeval diff;
433
434 if (tv_diff(now, barrier, &diff) > 0)
435 return 0;
436 sched_request_timeout(&diff, s);
437 return 1;
438 }
439
440 /**
441 * Force the next select() call to return before the given time.
442 *
443 * \param barrier Absolute time before select() should return.
444 * \param s Pointer to the scheduler struct.
445 *
446 * \return If \a barrier is in the past, this function requests a minimal
447 * timeout and returns zero. Otherwise it returns one.
448 *
449 * \sa sched_min_delay(), sched_request_barrier().
450 */
451 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
452 {
453 struct timeval diff;
454
455 if (tv_diff(now, barrier, &diff) > 0) {
456 sched_min_delay(s);
457 return 0;
458 }
459 sched_request_timeout(&diff, s);
460 return 1;
461 }