1 /* Copyright (C) 2006 Andre Noll <maan@tuebingen.mpg.de>, see file COPYING. */
3 /** \file sched.c Paraslash's scheduling functions. */
17 * The possible states of a task.
19 * In addition to the states listed here, a task may also enter zombie state.
20 * This happens when its ->post_select function returns negative, the ->status
21 * field is then set to this return value. Such tasks are not scheduled any
22 * more (i.e. ->pre_select() and ->post_select() are no longer called), but
23 * they stay on the scheduler task list until \ref task_reap() or
24 * \ref sched_shutdown() is called.
27 /** Task has been reaped and may be removed from the task list. */
29 /** Task is active. */
34 /** A copy of the task name supplied when the task was registered. */
36 /** Copied during task_register(). */
37 struct task_info info;
38 /* TS_RUNNING, TS_DEAD, or zombie (negative value). */
40 /** Position of the task in the task list of the scheduler. */
41 struct list_head node;
42 /** If less than zero, the task was notified by another task. */
46 static struct timeval now_struct;
47 const struct timeval *now = &now_struct;
49 static void sched_preselect(struct sched *s)
53 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
56 if (t->notification != 0)
58 if (t->info.pre_select)
59 t->info.pre_select(s, t->info.context);
63 static void unlink_and_free_task(struct task *t)
65 PARA_INFO_LOG("freeing task %s (%s)\n", t->name, t->status < 0?
66 para_strerror(-t->status) :
67 (t->status == TS_DEAD? "[dead]" : "[running]"));
74 //#define SCHED_DEBUG 1
75 static inline void call_post_select(struct sched *s, struct task *t)
80 ret = t->info.post_select(s, t->info.context);
82 struct timeval t1, t2, diff;
85 clock_get_realtime(&t1);
86 ret = t->info.post_select(s, t->info.context);
87 clock_get_realtime(&t2);
88 tv_diff(&t1, &t2, &diff);
91 PARA_WARNING_LOG("%s: post_select time: %lums\n",
94 t->status = ret < 0? ret : TS_RUNNING;
97 static unsigned sched_post_select(struct sched *s)
100 unsigned num_running_tasks = 0;
102 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
103 if (t->status == TS_DEAD) /* task has been reaped */
104 unlink_and_free_task(t);
105 else if (t->status == TS_RUNNING) {
106 call_post_select(s, t); /* sets t->status */
108 if (t->status == TS_RUNNING)
112 return num_running_tasks;
116 * The core function of all paraslash programs.
118 * \param s Pointer to the scheduler struct.
120 * This function updates the global \a now pointer, calls all registered
121 * pre_select hooks which may set the timeout and add any file descriptors to
122 * the fd sets of \a s. Next, it calls para_select() and makes the result available
123 * to the registered tasks by calling their post_select hook.
125 * \return Zero if no more tasks are left in the task list, negative if the
126 * select function returned an error.
130 int schedule(struct sched *s)
133 unsigned num_running_tasks;
135 if (!s->select_function)
136 s->select_function = para_select;
140 s->select_timeout = s->default_timeout;
142 clock_get_realtime(&now_struct);
144 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
150 * APUE: Be careful not to check the descriptor sets on return
151 * unless the return value is greater than zero. The return
152 * state of the descriptor sets is implementation dependent if
153 * either a signal is caught or the timer expires.
158 clock_get_realtime(&now_struct);
159 num_running_tasks = sched_post_select(s);
160 if (num_running_tasks == 0)
166 * Obtain the error status of a task and deallocate its resources.
168 * \param tptr Identifies the task to reap.
170 * This function is similar to wait(2) in that it returns information about a
171 * terminated task which allows releasing the resources associated with the
172 * task. Until this function is called, the terminated task remains in a zombie
175 * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
176 * nothing and returns zero. Otherwise, it is checked whether the task
177 * identified by \a tptr is still running. If it is, the function returns zero
178 * and again, no action is taken. Otherwise the (negative) error code of the
179 * terminated task is returned and \a *tptr is set to \p NULL. The task will
180 * then be removed removed from the scheduler task list.
182 * \sa \ref sched_shutdown(), wait(2).
184 int task_reap(struct task **tptr)
198 * With list_for_each_entry_safe() it is only safe to remove the
199 * _current_ list item. Since we are being called from the loop in
200 * schedule() via some task's ->post_select() function, freeing the
201 * given task here would result in use-after-free bugs in schedule().
202 * So we only set the task status to TS_DEAD which tells schedule() to
203 * free the task in the next iteration of its loop.
212 * Deallocate all resources of all tasks of a scheduler instance.
214 * \param s The scheduler instance.
216 * This should only be called after \ref schedule() has returned.
218 void sched_shutdown(struct sched *s)
220 struct task *t, *tmp;
222 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
223 if (t->status == TS_RUNNING)
224 /* The task list should contain only terminated tasks. */
225 PARA_WARNING_LOG("shutting down running task %s\n",
227 unlink_and_free_task(t);
232 * Add a task to the scheduler task list.
234 * \param info Task information supplied by the caller.
235 * \param s The scheduler instance.
237 * \return A pointer to a newly allocated task structure. It will be
238 * freed by sched_shutdown().
240 struct task *task_register(struct task_info *info, struct sched *s)
242 struct task *t = para_malloc(sizeof(*t));
244 assert(info->post_select);
246 if (!s->task_list.next)
247 INIT_LIST_HEAD(&s->task_list);
250 t->name = para_strdup(info->name);
252 t->status = TS_RUNNING;
253 list_add_tail(&t->node, &s->task_list);
258 * Get the list of all registered tasks.
260 * \param s The scheduler instance to get the task list from.
262 * \return The task list.
264 * Each entry of the list contains an identifier which is simply a hex number.
265 * The result is dynamically allocated and must be freed by the caller.
267 char *get_task_list(struct sched *s)
269 struct task *t, *tmp;
272 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
274 tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
275 t->status == TS_DEAD? "dead" :
276 (t->status == TS_RUNNING? "running" : "zombie"),
285 * Set the notification value of a task.
287 * \param t The task to notify.
288 * \param err A positive error code.
290 * Tasks which honor notifications are supposed to call \ref
291 * task_get_notification() in their post_select function and act on the
292 * returned notification value.
294 * If the scheduler detects during its pre_select loop that at least one task
295 * has been notified, the loop terminates, and the post_select methods of all
296 * taks are immediately called again.
298 * The notification for a task is reset after the call to its post_select
301 * \sa \ref task_get_notification().
303 void task_notify(struct task *t, int err)
306 if (t->notification == -err) /* ignore subsequent notifications */
308 PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
309 t->notification = -err;
313 * Return the notification value of a task.
315 * \param t The task to get the notification value from.
317 * \return The notification value. If this is negative, the task has been
318 * notified by another task. Tasks are supposed to check for notifications by
319 * calling this function from their post_select method.
321 * \sa \ref task_notify().
323 int task_get_notification(const struct task *t)
325 return t->notification;
329 * Return the status value of a task.
331 * \param t The task to get the status value from.
333 * \return Zero if task does not exist, one if task is running, negative error
334 * code if task has terminated.
336 int task_status(const struct task *t)
340 if (t->status == TS_DEAD) /* pretend dead tasks don't exist */
342 if (t->status == TS_RUNNING)
348 * Set the notification value of all tasks of a scheduler instance.
350 * \param s The scheduler instance whose tasks should be notified.
351 * \param err A positive error code.
353 * This simply iterates over all existing tasks of \a s and sets each
354 * task's notification value to \p -err.
356 void task_notify_all(struct sched *s, int err)
360 list_for_each_entry(t, &s->task_list, node)
365 * Set the select timeout to the minimal possible value.
367 * \param s Pointer to the scheduler struct.
369 * This causes the next select() call to return immediately.
371 void sched_min_delay(struct sched *s)
373 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
377 * Impose an upper bound for the timeout of the next select() call.
379 * \param to Maximal allowed timeout.
380 * \param s Pointer to the scheduler struct.
382 * If the current scheduler timeout is already smaller than \a to, this
383 * function does nothing. Otherwise the timeout for the next select() call is
384 * set to the given value.
386 * \sa \ref sched_request_timeout_ms().
388 void sched_request_timeout(struct timeval *to, struct sched *s)
390 if (tv_diff(&s->select_timeout, to, NULL) > 0)
391 s->select_timeout = *to;
395 * Force the next select() call to return before the given amount of milliseconds.
397 * \param ms The maximal allowed timeout in milliseconds.
398 * \param s Pointer to the scheduler struct.
400 * Like sched_request_timeout() this imposes an upper bound on the timeout
401 * value for the next select() call.
403 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
407 sched_request_timeout(&tv, s);
411 * Force the next select() call to return before the given future time.
413 * \param barrier Absolute time before select() should return.
414 * \param s Pointer to the scheduler struct.
416 * \return If \a barrier is in the past, this function does nothing and returns
417 * zero. Otherwise it returns one.
419 * \sa \ref sched_request_barrier_or_min_delay().
421 int sched_request_barrier(struct timeval *barrier, struct sched *s)
425 if (tv_diff(now, barrier, &diff) > 0)
427 sched_request_timeout(&diff, s);
432 * Force the next select() call to return before the given time.
434 * \param barrier Absolute time before select() should return.
435 * \param s Pointer to the scheduler struct.
437 * \return If \a barrier is in the past, this function requests a minimal
438 * timeout and returns zero. Otherwise it returns one.
440 * \sa \ref sched_min_delay(), \ref sched_request_barrier().
442 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
446 if (tv_diff(now, barrier, &diff) > 0) {
450 sched_request_timeout(&diff, s);