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 /** The task name supplied when the task was registered(). */
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). */
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. */
34 /** True if task is in error state and exit status has been queried. */
36 /** Usually a pointer to the struct containing this task. */
40 static struct timeval now_struct
;
41 struct timeval
*now
= &now_struct
;
43 static inline bool timeout_is_zero(struct sched
*s
)
45 struct timeval
*tv
= &s
->select_timeout
;
46 return tv
->tv_sec
== 0 && tv
->tv_usec
== 0;
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)
63 static void unlink_and_free_task(struct task
*t
)
65 PARA_INFO_LOG("freeing task %s\n", t
->name
);
71 //#define SCHED_DEBUG 1
72 static inline void call_post_select(struct sched
*s
, struct task
*t
)
75 t
->status
= t
->post_select(s
, t
);
77 struct timeval t1
, t2
, diff
;
80 clock_get_realtime(&t1
);
81 t
->status
= t
->post_select(s
, t
);
82 clock_get_realtime(&t2
);
83 tv_diff(&t1
, &t2
, &diff
);
86 PARA_WARNING_LOG("%s: post_select time: %lums\n",
91 static unsigned sched_post_select(struct sched
*s
)
94 unsigned num_running_tasks
= 0;
96 list_for_each_entry_safe(t
, tmp
, &s
->task_list
, node
) {
98 if (t
->dead
) /* task has been reaped */
99 unlink_and_free_task(t
);
102 call_post_select(s
, t
);
107 return num_running_tasks
;
111 * The core function of all paraslash programs.
113 * \param s Pointer to the scheduler struct.
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.
120 * \return Zero if no more tasks are left in the task list, negative if the
121 * select function returned an error.
123 * \sa \ref task, \ref now.
125 int schedule(struct sched
*s
)
128 unsigned num_running_tasks
;
130 if (!s
->select_function
)
131 s
->select_function
= para_select
;
135 s
->select_timeout
= s
->default_timeout
;
137 clock_get_realtime(now
);
139 ret
= s
->select_function(s
->max_fileno
+ 1, &s
->rfds
, &s
->wfds
,
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.
153 clock_get_realtime(now
);
154 num_running_tasks
= sched_post_select(s
);
155 if (num_running_tasks
== 0)
161 * Obtain the error status of a task and deallocate its resources.
163 * \param tptr Identifies the task to reap.
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
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.
177 * \sa \ref sched_shutdown(), wait(2).
179 int task_reap(struct task
**tptr
)
190 if (t
->dead
) /* will be freed in sched_post_select() */
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.
206 * Deallocate all resources of all tasks of a scheduler instance.
208 * \param s The scheduler instance.
210 * This should only be called after \ref schedule() has returned.
212 void sched_shutdown(struct sched
*s
)
214 struct task
*t
, *tmp
;
216 list_for_each_entry_safe(t
, tmp
, &s
->task_list
, node
) {
218 /* The task list should contain only terminated tasks. */
219 PARA_WARNING_LOG("shutting down running task %s\n",
221 unlink_and_free_task(t
);
226 * Add a task to the scheduler task list.
228 * \param info Task information supplied by the caller.
229 * \param s The scheduler instance.
231 * \return A pointer to a newly allocated task structure. It will be
232 * freed by sched_shutdown().
234 struct task
*task_register(struct task_info
*info
, struct sched
*s
)
236 struct task
*t
= para_malloc(sizeof(*t
));
238 assert(info
->post_select
);
240 if (!s
->task_list
.next
)
241 INIT_LIST_HEAD(&s
->task_list
);
243 t
->name
= para_strdup(info
->name
);
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
);
255 * Obtain the context pointer of a task.
257 * \param t Return this task's context pointer.
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().
262 void *task_context(struct task
*t
)
268 * Get the list of all registered tasks.
270 * \param s The scheduler instance to get the task list from.
272 * \return The task list.
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.
277 char *get_task_list(struct sched
*s
)
279 struct task
*t
, *tmp
;
282 list_for_each_entry_safe(t
, tmp
, &s
->task_list
, node
) {
284 tmp_msg
= make_message("%s%p\t%s\t%s\n", msg
? msg
: "", t
,
285 t
->status
< 0? (t
->dead
? "dead" : "zombie") : "running",
294 * Set the notification value of a task.
296 * \param t The task to notify.
297 * \param err A positive error code.
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.
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.
307 * The notification for a task is reset after the call to its post_select
310 * \sa \ref task_get_notification().
312 void task_notify(struct task
*t
, int err
)
315 if (t
->notification
== -err
) /* ignore subsequent notifications */
317 PARA_INFO_LOG("notifying task %s: %s\n", t
->name
, para_strerror(err
));
318 t
->notification
= -err
;
322 * Return the notification value of a task.
324 * \param t The task to get the notification value from.
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.
330 * \sa \ref task_notify().
332 int task_get_notification(const struct task
*t
)
334 return t
->notification
;
338 * Return the status value of a task.
340 * \param t The task to get the status value from.
342 * \return Zero if task does not exist, one if task is running, negative error
343 * code if task has terminated.
345 int task_status(const struct task
*t
)
357 * Set the notification value of all tasks of a scheduler instance.
359 * \param s The scheduler instance whose tasks should be notified.
360 * \param err A positive error code.
362 * This simply iterates over all existing tasks of \a s and sets each
363 * task's notification value to \p -err.
365 void task_notify_all(struct sched
*s
, int err
)
369 list_for_each_entry(t
, &s
->task_list
, node
)
374 * Set the select timeout to the minimal possible value.
376 * \param s Pointer to the scheduler struct.
378 * This causes the next select() call to return immediately.
380 void sched_min_delay(struct sched
*s
)
382 s
->select_timeout
.tv_sec
= s
->select_timeout
.tv_usec
= 0;
386 * Impose an upper bound for the timeout of the next select() call.
388 * \param to Maximal allowed timeout.
389 * \param s Pointer to the scheduler struct.
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.
395 * \sa sched_request_timeout_ms().
397 void sched_request_timeout(struct timeval
*to
, struct sched
*s
)
399 if (tv_diff(&s
->select_timeout
, to
, NULL
) > 0)
400 s
->select_timeout
= *to
;
404 * Force the next select() call to return before the given amount of milliseconds.
406 * \param ms The maximal allowed timeout in milliseconds.
407 * \param s Pointer to the scheduler struct.
409 * Like sched_request_timeout() this imposes an upper bound on the timeout
410 * value for the next select() call.
412 void sched_request_timeout_ms(long unsigned ms
, struct sched
*s
)
416 sched_request_timeout(&tv
, s
);
420 * Force the next select() call to return before the given future time.
422 * \param barrier Absolute time before select() should return.
423 * \param s Pointer to the scheduler struct.
425 * \return If \a barrier is in the past, this function does nothing and returns
426 * zero. Otherwise it returns one.
428 * \sa sched_request_barrier_or_min_delay().
430 int sched_request_barrier(struct timeval
*barrier
, struct sched
*s
)
434 if (tv_diff(now
, barrier
, &diff
) > 0)
436 sched_request_timeout(&diff
, s
);
441 * Force the next select() call to return before the given time.
443 * \param barrier Absolute time before select() should return.
444 * \param s Pointer to the scheduler struct.
446 * \return If \a barrier is in the past, this function requests a minimal
447 * timeout and returns zero. Otherwise it returns one.
449 * \sa sched_min_delay(), sched_request_barrier().
451 int sched_request_barrier_or_min_delay(struct timeval
*barrier
, struct sched
*s
)
455 if (tv_diff(now
, barrier
, &diff
) > 0) {
459 sched_request_timeout(&diff
, s
);