sched.c

   1 /*
   2  * Copyright (C) 2006-2012 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 #include <sys/time.h>
  12
  13 #include "para.h"
  14 #include "ipc.h"
  15 #include "fd.h"
  16 #include "list.h"
  17 #include "sched.h"
  18 #include "string.h"
  19 #include "time.h"
  20 #include "error.h"
  21
  22 static struct timeval now_struct;
  23 struct timeval *now = &now_struct;
  24
  25 /*
  26  * Remove a task from the scheduler.
  27  *
  28  * \param t The task to remove.
  29  *
  30  * If the pre_select pointer of \a t is not \p NULL, it is removed from
  31  * the pre_select list of the scheduler. Same goes for \a post_select.
  32  */
  33 static void unregister_task(struct task *t)
  34 {
  35         assert(t->error < 0);
  36         PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
  37                 para_strerror(-t->error));
  38         if (t->pre_select)
  39                 list_del(&t->pre_select_node);
  40         if (t->post_select)
  41                 list_del(&t->post_select_node);
  42 }
  43
  44 static inline bool timeout_is_zero(struct sched *s)
  45 {
  46         struct timeval *tv = &s->select_timeout;
  47         return tv->tv_sec == 0 && tv->tv_usec == 0;
  48 }
  49
  50 static void sched_preselect(struct sched *s)
  51 {
  52         struct task *t, *tmp;
  53         list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
  54                 if (t->error < 0) {
  55                         unregister_task(t);
  56                         continue;
  57                 }
  58                 if (t->notification != 0) {
  59                         sched_min_delay(s);
  60                         break;
  61                 }
  62                 if (!t->pre_select)
  63                         continue;
  64                 t->pre_select(s, t);
  65                 if (timeout_is_zero(s))
  66                         break;
  67         }
  68 }
  69
  70 //#define SCHED_DEBUG 1
  71 static inline void call_post_select(struct sched *s, struct task *t)
  72 {
  73 #ifndef SCHED_DEBUG
  74         t->post_select(s, t);
  75 #else
  76         struct timeval t1, t2, diff;
  77         unsigned long pst;
  78
  79         gettimeofday(&t1, NULL);
  80         t->post_select(s, t);
  81         gettimeofday(&t2, NULL);
  82         tv_diff(&t1, &t2, &diff);
  83         pst = tv2ms(&diff);
  84         if (pst > 50)
  85                 PARA_WARNING_LOG("%s: post_select time: %lums\n",
  86                         t->status, pst);
  87 #endif
  88 }
  89
  90 static void sched_post_select(struct sched *s)
  91 {
  92         struct task *t, *tmp;
  93
  94         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
  95                 if (t->error >= 0)
  96                         call_post_select(s, t);
  97 //              PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
  98                 t->notification = 0;
  99                 if (t->error >= 0)
 100                         continue;
 101                 /*
 102                  * We have to check whether the list is empty because the call
 103                  * to ->post_select() might have called sched_shutdown(). In
 104                  * this case t has been unregistered already, so we must not
 105                  * unregister it again.
 106                  */
 107                 if (list_empty(&s->post_select_list))
 108                         return;
 109                 unregister_task(t);
 110         }
 111 }
 112
 113 /**
 114  * The core function for all paraslash programs.
 115  *
 116  * \param s Pointer to the scheduler struct.
 117  *
 118  * This function updates the global \a now pointer, calls all registered
 119  * pre_select hooks which may set the timeout and add any file descriptors to
 120  * the fd sets of \a s.  Next, it calls para_select() and makes the result available
 121  * to the registered tasks by calling their post_select hook.
 122  *
 123  * \return Zero if no more tasks are left in either of the two lists, negative
 124  * if para_select returned an error.
 125  *
 126  * \sa task, now.
 127  */
 128 int schedule(struct sched *s)
 129 {
 130         int ret;
 131
 132         if (!s->select_function)
 133                 s->select_function = para_select;
 134 again:
 135         FD_ZERO(&s->rfds);
 136         FD_ZERO(&s->wfds);
 137         s->select_timeout = s->default_timeout;
 138         s->max_fileno = -1;
 139         gettimeofday(now, NULL);
 140         sched_preselect(s);
 141         if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
 142                 return 0;
 143         if (!timeout_is_zero(s)) {
 144                 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
 145                         &s->select_timeout);
 146                 if (ret < 0)
 147                         return ret;
 148                 if (ret == 0) {
 149                         /*
 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.
 154                          */
 155                         FD_ZERO(&s->rfds);
 156                         FD_ZERO(&s->wfds);
 157                 }
 158                 gettimeofday(now, NULL);
 159         } else {
 160                 FD_ZERO(&s->rfds);
 161                 FD_ZERO(&s->wfds);
 162         }
 163         sched_post_select(s);
 164         if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
 165                 return 0;
 166         goto again;
 167 }
 168
 169 /**
 170  * Add a task to the scheduler.
 171  *
 172  * \param t The task to add.
 173  * \param s The scheduler instance to add the task to.
 174  *
 175  * If the pre_select pointer of \a t is not \p NULL, it is added to
 176  * the pre_select list of the scheduler. Same goes for post_select.
 177  *
 178  * \sa task::pre_select, task::post_select
 179  */
 180 void register_task(struct sched *s, struct task *t)
 181 {
 182         PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
 183         t->notification = 0;
 184         if (!s->pre_select_list.next)
 185                 INIT_LIST_HEAD(&s->pre_select_list);
 186         if (!s->post_select_list.next)
 187                 INIT_LIST_HEAD(&s->post_select_list);
 188         if (t->pre_select) {
 189                 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
 190                 list_add_tail(&t->pre_select_node, &s->pre_select_list);
 191         }
 192         if (t->post_select) {
 193                 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
 194                 list_add_tail(&t->post_select_node, &s->post_select_list);
 195         }
 196 }
 197
 198 /**
 199  * Unregister all tasks.
 200  *
 201  * \param s The scheduler instance to shut down.
 202  *
 203  * This will cause \a schedule() to return immediately because both the
 204  * \a pre_select_list and the \a post_select_list are empty. This function
 205  * must be called from the post_select (rather than the pre_select) method.
 206  */
 207 void sched_shutdown(struct sched *s)
 208 {
 209         struct task *t, *tmp;
 210
 211         list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
 212                 t->error = -E_SCHED_SHUTDOWN;
 213                 unregister_task(t);
 214         }
 215         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
 216                 t->error = -E_SCHED_SHUTDOWN;
 217                 unregister_task(t);
 218         }
 219 }
 220
 221 /**
 222  * Get the list of all registered tasks.
 223  *
 224  * \param s The scheduler instance to get the task list from.
 225  *
 226  * \return The task list.
 227  *
 228  * Each entry of the list contains an identifier which is simply a hex number.
 229  * The result is dynamically allocated and must be freed by the caller.
 230  */
 231 char *get_task_list(struct sched *s)
 232 {
 233         struct task *t, *tmp;
 234         char *msg = NULL;
 235
 236         list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
 237                 char *tmp_msg;
 238                 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
 239                 free(msg);
 240                 msg = tmp_msg;
 241         }
 242         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
 243                 char *tmp_msg;
 244 //              if (t->pre_select)
 245 //                      continue;
 246                 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
 247                 free(msg);
 248                 msg = tmp_msg;
 249         }
 250         //PARA_DEBUG_LOG("task list:\n%s", msg);
 251         return msg;
 252 }
 253
 254 /**
 255  * Set the notification value of a task.
 256  *
 257  * \param t The task to notify.
 258  * \param err A positive error code.
 259  *
 260  * Tasks which honor notifications are supposed to call \ref
 261  * task_get_notification() in their post_select function and act on the
 262  * returned notification value.
 263  *
 264  * If the scheduler detects during its pre_select loop that at least one task
 265  * has been notified, the loop terminates, and the post_select methods of all
 266  * taks are immediately called again.
 267  *
 268  * The notification for a task is reset after the call to its post_select
 269  * method.
 270  *
 271  * \sa \ref task_get_notification().
 272  */
 273 void task_notify(struct task *t, int err)
 274 {
 275         assert(err > 0);
 276         if (t->notification == -err) /* ignore subsequent notifications */
 277                 return;
 278         PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
 279         t->notification = -err;
 280 }
 281
 282 /**
 283  * Return the notification value of a task.
 284  *
 285  * \param t The task to get the notification value from.
 286  *
 287  * \return The notification value. If this is negative, the task has been
 288  * notified by another task. Tasks are supposed to check for notifications by
 289  * calling this function from their post_select method.
 290  *
 291  * \sa \ref task_notify().
 292  */
 293 int task_get_notification(struct task *t)
 294 {
 295         return t->notification;
 296 }
 297
 298 /**
 299  * Set the select timeout to the minimal possible value.
 300  *
 301  * \param s Pointer to the scheduler struct.
 302  *
 303  * This causes the next select() call to return immediately.
 304  */
 305 void sched_min_delay(struct sched *s)
 306 {
 307         s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
 308 }
 309
 310 /**
 311  * Impose an upper bound for the timeout of the next select() call.
 312  *
 313  * \param to Maximal allowed timeout.
 314  * \param s Pointer to the scheduler struct.
 315  *
 316  * If the current scheduler timeout is already smaller than \a to, this
 317  * function does nothing. Otherwise the timeout for the next select() call is
 318  * set to the given value.
 319  *
 320  * \sa sched_request_timeout_ms().
 321  */
 322 void sched_request_timeout(struct timeval *to, struct sched *s)
 323 {
 324         if (tv_diff(&s->select_timeout, to, NULL) > 0)
 325                 s->select_timeout = *to;
 326 }
 327
 328 /**
 329  * Force the next select() call to return before the given amount of milliseconds.
 330  *
 331  * \param ms The maximal allowed timeout in milliseconds.
 332  * \param s Pointer to the scheduler struct.
 333  *
 334  * Like sched_request_timeout() this imposes an upper bound on the timeout
 335  * value for the next select() call.
 336  */
 337 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
 338 {
 339         struct timeval tv;
 340         ms2tv(ms, &tv);
 341         sched_request_timeout(&tv, s);
 342 }
 343
 344 /**
 345  * Force the next select() call to return before the given future time.
 346  *
 347  * \param barrier Absolute time before select() should return.
 348  * \param s Pointer to the scheduler struct.
 349  *
 350  * \return If \a barrier is in the past, this function does nothing and returns
 351  * zero. Otherwise it returns one.
 352  *
 353  * \sa sched_request_barrier_or_min_delay().
 354  */
 355 int sched_request_barrier(struct timeval *barrier, struct sched *s)
 356 {
 357         struct timeval diff;
 358
 359         if (tv_diff(now, barrier, &diff) > 0)
 360                 return 0;
 361         sched_request_timeout(&diff, s);
 362         return 1;
 363 }
 364
 365 /**
 366  * Force the next select() call to return before the given time.
 367  *
 368  * \param barrier Absolute time before select() should return.
 369  * \param s Pointer to the scheduler struct.
 370  *
 371  * \return If \a barrier is in the past, this function requests a minimal
 372  * timeout and returns zero. Otherwise it returns one.
 373  *
 374  * \sa sched_min_delay(), sched_request_barrier().
 375  */
 376 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
 377 {
 378         struct timeval diff;
 379
 380         if (tv_diff(now, barrier, &diff) > 0) {
 381                 sched_min_delay(s);
 382                 return 0;
 383         }
 384         sched_request_timeout(&diff, s);
 385         return 1;
 386 }