sched.c

   1 /*
   2  * Copyright (C) 2006-2013 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 static struct timeval now_struct;
  22 struct timeval *now = &now_struct;
  23
  24 /*
  25  * Remove a task from the scheduler.
  26  *
  27  * \param t The task to remove.
  28  *
  29  * If the pre_select pointer of \a t is not \p NULL, it is removed from
  30  * the pre_select list of the scheduler. Same goes for \a post_select.
  31  */
  32 static void unregister_task(struct task *t)
  33 {
  34         assert(t->error < 0);
  35         PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
  36                 para_strerror(-t->error));
  37         if (t->pre_select)
  38                 list_del(&t->pre_select_node);
  39         if (t->post_select)
  40                 list_del(&t->post_select_node);
  41 }
  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->pre_select_list, pre_select_node) {
  54                 if (t->notification != 0)
  55                         sched_min_delay(s);
  56                 if (t->pre_select)
  57                         t->pre_select(s, t);
  58         }
  59 }
  60
  61 //#define SCHED_DEBUG 1
  62 static inline void call_post_select(struct sched *s, struct task *t)
  63 {
  64 #ifndef SCHED_DEBUG
  65         t->error = t->post_select(s, t);
  66 #else
  67         struct timeval t1, t2, diff;
  68         unsigned long pst;
  69
  70         clock_get_realtime(&t1);
  71         t->error = t->post_select(s, t);
  72         clock_get_realtime(&t2);
  73         tv_diff(&t1, &t2, &diff);
  74         pst = tv2ms(&diff);
  75         if (pst > 50)
  76                 PARA_WARNING_LOG("%s: post_select time: %lums\n",
  77                         t->status, pst);
  78 #endif
  79 }
  80
  81 static void sched_post_select(struct sched *s)
  82 {
  83         struct task *t, *tmp;
  84
  85         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
  86                 if (t->error >= 0)
  87                         call_post_select(s, t);
  88 //              PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
  89                 t->notification = 0;
  90                 if (t->error >= 0)
  91                         continue;
  92                 unregister_task(t);
  93         }
  94 }
  95
  96 /**
  97  * The core function for all paraslash programs.
  98  *
  99  * \param s Pointer to the scheduler struct.
 100  *
 101  * This function updates the global \a now pointer, calls all registered
 102  * pre_select hooks which may set the timeout and add any file descriptors to
 103  * the fd sets of \a s.  Next, it calls para_select() and makes the result available
 104  * to the registered tasks by calling their post_select hook.
 105  *
 106  * \return Zero if no more tasks are left in either of the two lists, negative
 107  * if para_select returned an error.
 108  *
 109  * \sa task, now.
 110  */
 111 int schedule(struct sched *s)
 112 {
 113         int ret;
 114
 115         if (!s->select_function)
 116                 s->select_function = para_select;
 117 again:
 118         FD_ZERO(&s->rfds);
 119         FD_ZERO(&s->wfds);
 120         s->select_timeout = s->default_timeout;
 121         s->max_fileno = -1;
 122         clock_get_realtime(now);
 123         sched_preselect(s);
 124         ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
 125                 &s->select_timeout);
 126         if (ret < 0)
 127                 return ret;
 128         if (ret == 0) {
 129                 /*
 130                  * APUE: Be careful not to check the descriptor sets on return
 131                  * unless the return value is greater than zero. The return
 132                  * state of the descriptor sets is implementation dependent if
 133                  * either a signal is caught or the timer expires.
 134                  */
 135                 FD_ZERO(&s->rfds);
 136                 FD_ZERO(&s->wfds);
 137         }
 138         clock_get_realtime(now);
 139         sched_post_select(s);
 140         if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
 141                 return 0;
 142         goto again;
 143 }
 144
 145 /**
 146  * Add a task to the scheduler.
 147  *
 148  * \param t The task to add.
 149  * \param s The scheduler instance to add the task to.
 150  *
 151  * If the pre_select pointer of \a t is not \p NULL, it is added to
 152  * the pre_select list of the scheduler. Same goes for post_select.
 153  *
 154  * \sa task::pre_select, task::post_select
 155  */
 156 void register_task(struct sched *s, struct task *t)
 157 {
 158         PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
 159         t->notification = 0;
 160         if (!s->pre_select_list.next)
 161                 INIT_LIST_HEAD(&s->pre_select_list);
 162         if (!s->post_select_list.next)
 163                 INIT_LIST_HEAD(&s->post_select_list);
 164         if (t->pre_select) {
 165                 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
 166                 list_add_tail(&t->pre_select_node, &s->pre_select_list);
 167         }
 168         if (t->post_select) {
 169                 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
 170                 list_add_tail(&t->post_select_node, &s->post_select_list);
 171         }
 172 }
 173
 174 /**
 175  * Get the list of all registered tasks.
 176  *
 177  * \param s The scheduler instance to get the task list from.
 178  *
 179  * \return The task list.
 180  *
 181  * Each entry of the list contains an identifier which is simply a hex number.
 182  * The result is dynamically allocated and must be freed by the caller.
 183  */
 184 char *get_task_list(struct sched *s)
 185 {
 186         struct task *t, *tmp;
 187         char *msg = NULL;
 188
 189         list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
 190                 char *tmp_msg;
 191                 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
 192                 free(msg);
 193                 msg = tmp_msg;
 194         }
 195         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
 196                 char *tmp_msg;
 197 //              if (t->pre_select)
 198 //                      continue;
 199                 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
 200                 free(msg);
 201                 msg = tmp_msg;
 202         }
 203         //PARA_DEBUG_LOG("task list:\n%s", msg);
 204         return msg;
 205 }
 206
 207 /**
 208  * Set the notification value of a task.
 209  *
 210  * \param t The task to notify.
 211  * \param err A positive error code.
 212  *
 213  * Tasks which honor notifications are supposed to call \ref
 214  * task_get_notification() in their post_select function and act on the
 215  * returned notification value.
 216  *
 217  * If the scheduler detects during its pre_select loop that at least one task
 218  * has been notified, the loop terminates, and the post_select methods of all
 219  * taks are immediately called again.
 220  *
 221  * The notification for a task is reset after the call to its post_select
 222  * method.
 223  *
 224  * \sa \ref task_get_notification().
 225  */
 226 void task_notify(struct task *t, int err)
 227 {
 228         assert(err > 0);
 229         if (t->notification == -err) /* ignore subsequent notifications */
 230                 return;
 231         PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
 232         t->notification = -err;
 233 }
 234
 235 /**
 236  * Return the notification value of a task.
 237  *
 238  * \param t The task to get the notification value from.
 239  *
 240  * \return The notification value. If this is negative, the task has been
 241  * notified by another task. Tasks are supposed to check for notifications by
 242  * calling this function from their post_select method.
 243  *
 244  * \sa \ref task_notify().
 245  */
 246 int task_get_notification(struct task *t)
 247 {
 248         return t->notification;
 249 }
 250
 251 /**
 252  * Set the notification value of all tasks of a scheduler instance.
 253  *
 254  * \param s The scheduler instance whose tasks should be notified.
 255  * \param err A positive error code.
 256  *
 257  * This simply iterates over all existing tasks of \a s and sets each
 258  * task's notification value to \p -err.
 259  */
 260 void task_notify_all(struct sched *s, int err)
 261 {
 262         struct task *t;
 263
 264         list_for_each_entry(t, &s->pre_select_list, pre_select_node)
 265                 task_notify(t, err);
 266         list_for_each_entry(t, &s->post_select_list, post_select_node)
 267                 task_notify(t, err);
 268 }
 269
 270 /**
 271  * Set the select timeout to the minimal possible value.
 272  *
 273  * \param s Pointer to the scheduler struct.
 274  *
 275  * This causes the next select() call to return immediately.
 276  */
 277 void sched_min_delay(struct sched *s)
 278 {
 279         s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
 280 }
 281
 282 /**
 283  * Impose an upper bound for the timeout of the next select() call.
 284  *
 285  * \param to Maximal allowed timeout.
 286  * \param s Pointer to the scheduler struct.
 287  *
 288  * If the current scheduler timeout is already smaller than \a to, this
 289  * function does nothing. Otherwise the timeout for the next select() call is
 290  * set to the given value.
 291  *
 292  * \sa sched_request_timeout_ms().
 293  */
 294 void sched_request_timeout(struct timeval *to, struct sched *s)
 295 {
 296         if (tv_diff(&s->select_timeout, to, NULL) > 0)
 297                 s->select_timeout = *to;
 298 }
 299
 300 /**
 301  * Force the next select() call to return before the given amount of milliseconds.
 302  *
 303  * \param ms The maximal allowed timeout in milliseconds.
 304  * \param s Pointer to the scheduler struct.
 305  *
 306  * Like sched_request_timeout() this imposes an upper bound on the timeout
 307  * value for the next select() call.
 308  */
 309 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
 310 {
 311         struct timeval tv;
 312         ms2tv(ms, &tv);
 313         sched_request_timeout(&tv, s);
 314 }
 315
 316 /**
 317  * Force the next select() call to return before the given future time.
 318  *
 319  * \param barrier Absolute time before select() should return.
 320  * \param s Pointer to the scheduler struct.
 321  *
 322  * \return If \a barrier is in the past, this function does nothing and returns
 323  * zero. Otherwise it returns one.
 324  *
 325  * \sa sched_request_barrier_or_min_delay().
 326  */
 327 int sched_request_barrier(struct timeval *barrier, struct sched *s)
 328 {
 329         struct timeval diff;
 330
 331         if (tv_diff(now, barrier, &diff) > 0)
 332                 return 0;
 333         sched_request_timeout(&diff, s);
 334         return 1;
 335 }
 336
 337 /**
 338  * Force the next select() call to return before the given time.
 339  *
 340  * \param barrier Absolute time before select() should return.
 341  * \param s Pointer to the scheduler struct.
 342  *
 343  * \return If \a barrier is in the past, this function requests a minimal
 344  * timeout and returns zero. Otherwise it returns one.
 345  *
 346  * \sa sched_min_delay(), sched_request_barrier().
 347  */
 348 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
 349 {
 350         struct timeval diff;
 351
 352         if (tv_diff(now, barrier, &diff) > 0) {
 353                 sched_min_delay(s);
 354                 return 0;
 355         }
 356         sched_request_timeout(&diff, s);
 357         return 1;
 358 }