2 * Copyright (C) 2006-2014 Andre Noll <maan@systemlinux.org>
4 * Licensed under the GPL v2. For licencing details see COPYING.
7 /** \file sched.c Paraslash's scheduling functions. */
22 /** A copy of the task name supplied when the task was registered. */
24 /** Copied during task_register(). */
25 struct task_info info;
26 /** Whether this task is active (>=0) or in error state (<0). */
28 /** Position of the task in the task list of the scheduler. */
29 struct list_head node;
30 /** If less than zero, the task was notified by another task. */
32 /** True if task is in error state and exit status has been queried. */
36 static struct timeval now_struct;
37 struct timeval *now = &now_struct;
39 static inline bool timeout_is_zero(struct sched *s)
41 struct timeval *tv = &s->select_timeout;
42 return tv->tv_sec == 0 && tv->tv_usec == 0;
45 static void sched_preselect(struct sched *s)
49 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
52 if (t->notification != 0)
54 if (t->info.pre_select)
55 t->info.pre_select(s, t);
59 static void unlink_and_free_task(struct task *t)
61 PARA_INFO_LOG("freeing task %s\n", t->name);
67 //#define SCHED_DEBUG 1
68 static inline void call_post_select(struct sched *s, struct task *t)
71 t->status = t->info.post_select(s, t);
73 struct timeval t1, t2, diff;
76 clock_get_realtime(&t1);
77 t->status = t->info.post_select(s, t);
78 clock_get_realtime(&t2);
79 tv_diff(&t1, &t2, &diff);
82 PARA_WARNING_LOG("%s: post_select time: %lums\n",
87 static unsigned sched_post_select(struct sched *s)
90 unsigned num_running_tasks = 0;
92 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
94 if (t->dead) /* task has been reaped */
95 unlink_and_free_task(t);
98 call_post_select(s, t);
103 return num_running_tasks;
107 * The core function of all paraslash programs.
109 * \param s Pointer to the scheduler struct.
111 * This function updates the global \a now pointer, calls all registered
112 * pre_select hooks which may set the timeout and add any file descriptors to
113 * the fd sets of \a s. Next, it calls para_select() and makes the result available
114 * to the registered tasks by calling their post_select hook.
116 * \return Zero if no more tasks are left in the task list, negative if the
117 * select function returned an error.
119 * \sa \ref task, \ref now.
121 int schedule(struct sched *s)
124 unsigned num_running_tasks;
126 if (!s->select_function)
127 s->select_function = para_select;
131 s->select_timeout = s->default_timeout;
133 clock_get_realtime(now);
135 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
141 * APUE: Be careful not to check the descriptor sets on return
142 * unless the return value is greater than zero. The return
143 * state of the descriptor sets is implementation dependent if
144 * either a signal is caught or the timer expires.
149 clock_get_realtime(now);
150 num_running_tasks = sched_post_select(s);
151 if (num_running_tasks == 0)
157 * Obtain the error status of a task and deallocate its resources.
159 * \param tptr Identifies the task to reap.
161 * This function is similar to wait(2) in that it returns information about a
162 * terminated task and allows to release the resources associated with the
163 * task. Until this function is called, the terminated task remains in a zombie
166 * \return If \a tptr is \p NULL, or \a *tptr is \p NULL, the function does
167 * nothing and returns zero. Otherwise, it is checked whether the task
168 * identified by \a tptr is still running. If it is, the function returns zero
169 * and again, no action is taken. Otherwise the (negative) error code of the
170 * terminated task is returned and \a *tptr is set to \p NULL. The task will
171 * then be removed removed from the scheduler task list.
173 * \sa \ref sched_shutdown(), wait(2).
175 int task_reap(struct task **tptr)
186 if (t->dead) /* will be freed in sched_post_select() */
189 * With list_for_each_entry_safe() it is only safe to remove the
190 * _current_ list item. Since we are being called from the loop in
191 * schedule() via some task's ->post_select() function, freeing the
192 * given task here would result in use-after-free bugs in schedule().
193 * So we only set t->dead which tells schedule() to free the task in
194 * the next iteration of its loop.
202 * Deallocate all resources of all tasks of a scheduler instance.
204 * \param s The scheduler instance.
206 * This should only be called after \ref schedule() has returned.
208 void sched_shutdown(struct sched *s)
210 struct task *t, *tmp;
212 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
214 /* The task list should contain only terminated tasks. */
215 PARA_WARNING_LOG("shutting down running task %s\n",
217 unlink_and_free_task(t);
222 * Add a task to the scheduler task list.
224 * \param info Task information supplied by the caller.
225 * \param s The scheduler instance.
227 * \return A pointer to a newly allocated task structure. It will be
228 * freed by sched_shutdown().
230 struct task *task_register(struct task_info *info, struct sched *s)
232 struct task *t = para_malloc(sizeof(*t));
234 assert(info->post_select);
236 if (!s->task_list.next)
237 INIT_LIST_HEAD(&s->task_list);
240 t->name = para_strdup(info->name);
244 list_add_tail(&t->node, &s->task_list);
249 * Obtain the context pointer of a task.
251 * \param t Return this task's context pointer.
253 * \return A pointer to the memory location specified previously as \a
254 * task_info->context when the task was registered with \ref task_register().
256 void *task_context(struct task *t)
258 return t->info.context;
262 * Get the list of all registered tasks.
264 * \param s The scheduler instance to get the task list from.
266 * \return The task list.
268 * Each entry of the list contains an identifier which is simply a hex number.
269 * The result is dynamically allocated and must be freed by the caller.
271 char *get_task_list(struct sched *s)
273 struct task *t, *tmp;
276 list_for_each_entry_safe(t, tmp, &s->task_list, node) {
278 tmp_msg = make_message("%s%p\t%s\t%s\n", msg? msg : "", t,
279 t->status < 0? (t->dead? "dead" : "zombie") : "running",
288 * Set the notification value of a task.
290 * \param t The task to notify.
291 * \param err A positive error code.
293 * Tasks which honor notifications are supposed to call \ref
294 * task_get_notification() in their post_select function and act on the
295 * returned notification value.
297 * If the scheduler detects during its pre_select loop that at least one task
298 * has been notified, the loop terminates, and the post_select methods of all
299 * taks are immediately called again.
301 * The notification for a task is reset after the call to its post_select
304 * \sa \ref task_get_notification().
306 void task_notify(struct task *t, int err)
309 if (t->notification == -err) /* ignore subsequent notifications */
311 PARA_INFO_LOG("notifying task %s: %s\n", t->name, para_strerror(err));
312 t->notification = -err;
316 * Return the notification value of a task.
318 * \param t The task to get the notification value from.
320 * \return The notification value. If this is negative, the task has been
321 * notified by another task. Tasks are supposed to check for notifications by
322 * calling this function from their post_select method.
324 * \sa \ref task_notify().
326 int task_get_notification(const struct task *t)
328 return t->notification;
332 * Return the status value of a task.
334 * \param t The task to get the status value from.
336 * \return Zero if task does not exist, one if task is running, negative error
337 * code if task has terminated.
339 int task_status(const struct task *t)
351 * Set the notification value of all tasks of a scheduler instance.
353 * \param s The scheduler instance whose tasks should be notified.
354 * \param err A positive error code.
356 * This simply iterates over all existing tasks of \a s and sets each
357 * task's notification value to \p -err.
359 void task_notify_all(struct sched *s, int err)
363 list_for_each_entry(t, &s->task_list, node)
368 * Set the select timeout to the minimal possible value.
370 * \param s Pointer to the scheduler struct.
372 * This causes the next select() call to return immediately.
374 void sched_min_delay(struct sched *s)
376 s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
380 * Impose an upper bound for the timeout of the next select() call.
382 * \param to Maximal allowed timeout.
383 * \param s Pointer to the scheduler struct.
385 * If the current scheduler timeout is already smaller than \a to, this
386 * function does nothing. Otherwise the timeout for the next select() call is
387 * set to the given value.
389 * \sa sched_request_timeout_ms().
391 void sched_request_timeout(struct timeval *to, struct sched *s)
393 if (tv_diff(&s->select_timeout, to, NULL) > 0)
394 s->select_timeout = *to;
398 * Force the next select() call to return before the given amount of milliseconds.
400 * \param ms The maximal allowed timeout in milliseconds.
401 * \param s Pointer to the scheduler struct.
403 * Like sched_request_timeout() this imposes an upper bound on the timeout
404 * value for the next select() call.
406 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
410 sched_request_timeout(&tv, s);
414 * Force the next select() call to return before the given future time.
416 * \param barrier Absolute time before select() should return.
417 * \param s Pointer to the scheduler struct.
419 * \return If \a barrier is in the past, this function does nothing and returns
420 * zero. Otherwise it returns one.
422 * \sa sched_request_barrier_or_min_delay().
424 int sched_request_barrier(struct timeval *barrier, struct sched *s)
428 if (tv_diff(now, barrier, &diff) > 0)
430 sched_request_timeout(&diff, s);
435 * Force the next select() call to return before the given time.
437 * \param barrier Absolute time before select() should return.
438 * \param s Pointer to the scheduler struct.
440 * \return If \a barrier is in the past, this function requests a minimal
441 * timeout and returns zero. Otherwise it returns one.
443 * \sa sched_min_delay(), sched_request_barrier().
445 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
449 if (tv_diff(now, barrier, &diff) > 0) {
453 sched_request_timeout(&diff, s);