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                 unregister_task(t);
 102         }
 103 }
 104
 105 /**
 106  * The core function for all paraslash programs.
 107  *
 108  * \param s Pointer to the scheduler struct.
 109  *
 110  * This function updates the global \a now pointer, calls all registered
 111  * pre_select hooks which may set the timeout and add any file descriptors to
 112  * the fd sets of \a s.  Next, it calls para_select() and makes the result available
 113  * to the registered tasks by calling their post_select hook.
 114  *
 115  * \return Zero if no more tasks are left in either of the two lists, negative
 116  * if para_select returned an error.
 117  *
 118  * \sa task, now.
 119  */
 120 int schedule(struct sched *s)
 121 {
 122         int ret;
 123
 124         if (!s->select_function)
 125                 s->select_function = para_select;
 126 again:
 127         FD_ZERO(&s->rfds);
 128         FD_ZERO(&s->wfds);
 129         s->select_timeout = s->default_timeout;
 130         s->max_fileno = -1;
 131         gettimeofday(now, NULL);
 132         sched_preselect(s);
 133         if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
 134                 return 0;
 135         if (!timeout_is_zero(s)) {
 136                 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
 137                         &s->select_timeout);
 138                 if (ret < 0)
 139                         return ret;
 140                 if (ret == 0) {
 141                         /*
 142                          * APUE: Be careful not to check the descriptor sets on return
 143                          * unless the return value is greater than zero. The return
 144                          * state of the descriptor sets is implementation dependent if
 145                          * either a signal is caught or the timer expires.
 146                          */
 147                         FD_ZERO(&s->rfds);
 148                         FD_ZERO(&s->wfds);
 149                 }
 150                 gettimeofday(now, NULL);
 151         } else {
 152                 FD_ZERO(&s->rfds);
 153                 FD_ZERO(&s->wfds);
 154         }
 155         sched_post_select(s);
 156         if (list_empty(&s->pre_select_list) && list_empty(&s->post_select_list))
 157                 return 0;
 158         goto again;
 159 }
 160
 161 /**
 162  * Add a task to the scheduler.
 163  *
 164  * \param t The task to add.
 165  * \param s The scheduler instance to add the task to.
 166  *
 167  * If the pre_select pointer of \a t is not \p NULL, it is added to
 168  * the pre_select list of the scheduler. Same goes for post_select.
 169  *
 170  * \sa task::pre_select, task::post_select
 171  */
 172 void register_task(struct sched *s, struct task *t)
 173 {
 174         PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
 175         t->notification = 0;
 176         if (!s->pre_select_list.next)
 177                 INIT_LIST_HEAD(&s->pre_select_list);
 178         if (!s->post_select_list.next)
 179                 INIT_LIST_HEAD(&s->post_select_list);
 180         if (t->pre_select) {
 181                 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
 182                 list_add_tail(&t->pre_select_node, &s->pre_select_list);
 183         }
 184         if (t->post_select) {
 185                 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
 186                 list_add_tail(&t->post_select_node, &s->post_select_list);
 187         }
 188 }
 189
 190 /**
 191  * Get the list of all registered tasks.
 192  *
 193  * \param s The scheduler instance to get the task list from.
 194  *
 195  * \return The task list.
 196  *
 197  * Each entry of the list contains an identifier which is simply a hex number.
 198  * The result is dynamically allocated and must be freed by the caller.
 199  */
 200 char *get_task_list(struct sched *s)
 201 {
 202         struct task *t, *tmp;
 203         char *msg = NULL;
 204
 205         list_for_each_entry_safe(t, tmp, &s->pre_select_list, pre_select_node) {
 206                 char *tmp_msg;
 207                 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
 208                 free(msg);
 209                 msg = tmp_msg;
 210         }
 211         list_for_each_entry_safe(t, tmp, &s->post_select_list, post_select_node) {
 212                 char *tmp_msg;
 213 //              if (t->pre_select)
 214 //                      continue;
 215                 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
 216                 free(msg);
 217                 msg = tmp_msg;
 218         }
 219         //PARA_DEBUG_LOG("task list:\n%s", msg);
 220         return msg;
 221 }
 222
 223 /**
 224  * Set the notification value of a task.
 225  *
 226  * \param t The task to notify.
 227  * \param err A positive error code.
 228  *
 229  * Tasks which honor notifications are supposed to call \ref
 230  * task_get_notification() in their post_select function and act on the
 231  * returned notification value.
 232  *
 233  * If the scheduler detects during its pre_select loop that at least one task
 234  * has been notified, the loop terminates, and the post_select methods of all
 235  * taks are immediately called again.
 236  *
 237  * The notification for a task is reset after the call to its post_select
 238  * method.
 239  *
 240  * \sa \ref task_get_notification().
 241  */
 242 void task_notify(struct task *t, int err)
 243 {
 244         assert(err > 0);
 245         if (t->notification == -err) /* ignore subsequent notifications */
 246                 return;
 247         PARA_INFO_LOG("notifying task %s: %s\n", t->status, para_strerror(err));
 248         t->notification = -err;
 249 }
 250
 251 /**
 252  * Return the notification value of a task.
 253  *
 254  * \param t The task to get the notification value from.
 255  *
 256  * \return The notification value. If this is negative, the task has been
 257  * notified by another task. Tasks are supposed to check for notifications by
 258  * calling this function from their post_select method.
 259  *
 260  * \sa \ref task_notify().
 261  */
 262 int task_get_notification(struct task *t)
 263 {
 264         return t->notification;
 265 }
 266
 267 /**
 268  * Set the notification value of all tasks of a scheduler instance.
 269  *
 270  * \param s The scheduler instance whose tasks should be notified.
 271  * \param err A positive error code.
 272  *
 273  * This simply iterates over all existing tasks of \a s and sets each
 274  * task's notification value to \p -err.
 275  */
 276 void task_notify_all(struct sched *s, int err)
 277 {
 278         struct task *t;
 279
 280         list_for_each_entry(t, &s->pre_select_list, pre_select_node)
 281                 task_notify(t, err);
 282         list_for_each_entry(t, &s->post_select_list, post_select_node)
 283                 task_notify(t, err);
 284 }
 285
 286 /**
 287  * Set the select timeout to the minimal possible value.
 288  *
 289  * \param s Pointer to the scheduler struct.
 290  *
 291  * This causes the next select() call to return immediately.
 292  */
 293 void sched_min_delay(struct sched *s)
 294 {
 295         s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
 296 }
 297
 298 /**
 299  * Impose an upper bound for the timeout of the next select() call.
 300  *
 301  * \param to Maximal allowed timeout.
 302  * \param s Pointer to the scheduler struct.
 303  *
 304  * If the current scheduler timeout is already smaller than \a to, this
 305  * function does nothing. Otherwise the timeout for the next select() call is
 306  * set to the given value.
 307  *
 308  * \sa sched_request_timeout_ms().
 309  */
 310 void sched_request_timeout(struct timeval *to, struct sched *s)
 311 {
 312         if (tv_diff(&s->select_timeout, to, NULL) > 0)
 313                 s->select_timeout = *to;
 314 }
 315
 316 /**
 317  * Force the next select() call to return before the given amount of milliseconds.
 318  *
 319  * \param ms The maximal allowed timeout in milliseconds.
 320  * \param s Pointer to the scheduler struct.
 321  *
 322  * Like sched_request_timeout() this imposes an upper bound on the timeout
 323  * value for the next select() call.
 324  */
 325 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
 326 {
 327         struct timeval tv;
 328         ms2tv(ms, &tv);
 329         sched_request_timeout(&tv, s);
 330 }
 331
 332 /**
 333  * Force the next select() call to return before the given future time.
 334  *
 335  * \param barrier Absolute time before select() should return.
 336  * \param s Pointer to the scheduler struct.
 337  *
 338  * \return If \a barrier is in the past, this function does nothing and returns
 339  * zero. Otherwise it returns one.
 340  *
 341  * \sa sched_request_barrier_or_min_delay().
 342  */
 343 int sched_request_barrier(struct timeval *barrier, struct sched *s)
 344 {
 345         struct timeval diff;
 346
 347         if (tv_diff(now, barrier, &diff) > 0)
 348                 return 0;
 349         sched_request_timeout(&diff, s);
 350         return 1;
 351 }
 352
 353 /**
 354  * Force the next select() call to return before the given time.
 355  *
 356  * \param barrier Absolute time before select() should return.
 357  * \param s Pointer to the scheduler struct.
 358  *
 359  * \return If \a barrier is in the past, this function requests a minimal
 360  * timeout and returns zero. Otherwise it returns one.
 361  *
 362  * \sa sched_min_delay(), sched_request_barrier().
 363  */
 364 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
 365 {
 366         struct timeval diff;
 367
 368         if (tv_diff(now, barrier, &diff) > 0) {
 369                 sched_min_delay(s);
 370                 return 0;
 371         }
 372         sched_request_timeout(&diff, s);
 373         return 1;
 374 }