sched.c

   1 /*
   2  * Copyright (C) 2006-2011 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 #include <stdbool.h>
  13
  14 #include "para.h"
  15 #include "ipc.h"
  16 #include "fd.h"
  17 #include "list.h"
  18 #include "sched.h"
  19 #include "string.h"
  20 #include "time.h"
  21 #include "error.h"
  22
  23 static struct list_head pre_select_list, post_select_list;
  24 static int initialized;
  25
  26 static struct timeval now_struct;
  27 struct timeval *now = &now_struct;
  28
  29 /*
  30  * Remove a task from the scheduler.
  31  *
  32  * \param t The task to remove.
  33  *
  34  * If the pre_select pointer of \a t is not \p NULL, it is removed from
  35  * the pre_select list of the scheduler. Same goes for \a post_select.
  36  */
  37 static void unregister_task(struct task *t)
  38 {
  39         if (!initialized)
  40                 return;
  41         assert(t->error < 0);
  42         PARA_INFO_LOG("unregistering %s (%s)\n", t->status,
  43                 para_strerror(-t->error));
  44         if (t->pre_select)
  45                 list_del(&t->pre_select_node);
  46         if (t->post_select)
  47                 list_del(&t->post_select_node);
  48 }
  49
  50 static inline bool timeout_is_zero(struct sched *s)
  51 {
  52         struct timeval *tv = &s->select_timeout;
  53         return tv->tv_sec == 0 && tv->tv_usec == 0;
  54 }
  55
  56 static void sched_preselect(struct sched *s)
  57 {
  58         struct task *t, *tmp;
  59         list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
  60                 if (t->error < 0) {
  61                         unregister_task(t);
  62                         continue;
  63                 }
  64                 if (!t->pre_select)
  65                         continue;
  66                 t->pre_select(s, t);
  67                 if (timeout_is_zero(s))
  68                         break;
  69         }
  70 }
  71
  72 //#define SCHED_DEBUG 1
  73 static inline void call_post_select(struct sched *s, struct task *t)
  74 {
  75 #ifndef SCHED_DEBUG
  76         t->post_select(s, t);
  77 #else
  78         struct timeval t1, t2, diff;
  79         unsigned long pst;
  80
  81         gettimeofday(&t1, NULL);
  82         t->post_select(s, t);
  83         gettimeofday(&t2, NULL);
  84         tv_diff(&t1, &t2, &diff);
  85         pst = tv2ms(&diff);
  86         if (pst > 50)
  87                 PARA_WARNING_LOG("%s: post_select time: %lums\n",
  88                         t->status, pst);
  89 #endif
  90 }
  91
  92 static void sched_post_select(struct sched *s)
  93 {
  94         struct task *t, *tmp;
  95
  96         list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
  97                 if (t->error >= 0)
  98                         call_post_select(s, t);
  99 //              PARA_INFO_LOG("%s: %d\n", t->status, t->ret);
 100                 if (t->error >= 0)
 101                         continue;
 102                 /*
 103                  * We have to check whether the list is empty because the call
 104                  * to ->post_select() might have called sched_shutdown(). In
 105                  * this case t has been unregistered already, so we must not
 106                  * unregister it again.
 107                  */
 108                 if (list_empty(&post_select_list))
 109                         return;
 110                 unregister_task(t);
 111         }
 112 }
 113
 114 /**
 115  * The core function for all paraslash programs.
 116  *
 117  * \param s Pointer to the scheduler struct.
 118  *
 119  * This function updates the global \a now pointer, calls all registered
 120  * pre_select hooks which may set the timeout and add any file descriptors to
 121  * the fd sets of \a s.  Next, it calls para_select() and makes the result available
 122  * to the registered tasks by calling their post_select hook.
 123  *
 124  * \return Zero if no more tasks are left in either of the two lists, negative
 125  * if para_select returned an error.
 126  *
 127  * \sa task, now.
 128  */
 129 int schedule(struct sched *s)
 130 {
 131         int ret;
 132
 133         if (!initialized)
 134                 return -E_NOT_INITIALIZED;
 135         if (!s->select_function)
 136                 s->select_function = para_select;
 137 again:
 138         FD_ZERO(&s->rfds);
 139         FD_ZERO(&s->wfds);
 140         s->select_timeout = s->default_timeout;
 141         s->max_fileno = -1;
 142         gettimeofday(now, NULL);
 143         sched_preselect(s);
 144         if (list_empty(&pre_select_list) && list_empty(&post_select_list))
 145                 return 0;
 146         if (!timeout_is_zero(s)) {
 147                 ret = s->select_function(s->max_fileno + 1, &s->rfds, &s->wfds,
 148                         &s->select_timeout);
 149                 if (ret < 0)
 150                         return ret;
 151                 if (ret == 0) {
 152                         /*
 153                          * APUE: Be careful not to check the descriptor sets on return
 154                          * unless the return value is greater than zero. The return
 155                          * state of the descriptor sets is implementation dependent if
 156                          * either a signal is caught or the timer expires.
 157                          */
 158                         FD_ZERO(&s->rfds);
 159                         FD_ZERO(&s->wfds);
 160                 }
 161                 gettimeofday(now, NULL);
 162         } else {
 163                 FD_ZERO(&s->rfds);
 164                 FD_ZERO(&s->wfds);
 165         }
 166         sched_post_select(s);
 167         if (list_empty(&pre_select_list) && list_empty(&post_select_list))
 168                 return 0;
 169         goto again;
 170 }
 171
 172 /*
 173  * Initialize the paraslash scheduler.
 174  */
 175 static void init_sched(void)
 176 {
 177         PARA_INFO_LOG("initializing scheduler\n");
 178         INIT_LIST_HEAD(&pre_select_list);
 179         INIT_LIST_HEAD(&post_select_list);
 180         initialized = 1;
 181 }
 182
 183 /**
 184  * Add a task to the scheduler.
 185  *
 186  * \param t the task to add
 187  *
 188  * If the pre_select pointer of \a t is not \p NULL, it is added to
 189  * the pre_select list of the scheduler. Same goes for post_select.
 190  *
 191  * \sa task::pre_select, task::post_select
 192  */
 193 void register_task(struct task *t)
 194 {
 195         if (!initialized)
 196                 init_sched();
 197         PARA_INFO_LOG("registering %s (%p)\n", t->status, t);
 198         if (t->pre_select) {
 199                 PARA_DEBUG_LOG("pre_select: %p\n", &t->pre_select);
 200                 list_add_tail(&t->pre_select_node, &pre_select_list);
 201         }
 202         if (t->post_select) {
 203                 PARA_DEBUG_LOG("post_select: %p\n", &t->post_select);
 204                 list_add_tail(&t->post_select_node, &post_select_list);
 205         }
 206 }
 207
 208 /**
 209  * Unregister all tasks.
 210  *
 211  * This will cause \a schedule() to return immediately because both the
 212  * \a pre_select_list and the \a post_select_list are empty. This function
 213  * must be called from the post_select (rather than the pre_select) method.
 214  */
 215 void sched_shutdown(void)
 216 {
 217         struct task *t, *tmp;
 218
 219         if (!initialized)
 220                 return;
 221         list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
 222                 t->error = -E_SCHED_SHUTDOWN;
 223                 unregister_task(t);
 224         }
 225         list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
 226                 t->error = -E_SCHED_SHUTDOWN;
 227                 unregister_task(t);
 228         }
 229         initialized = 0;
 230 }
 231
 232 /**
 233  * Get the list of all registered tasks.
 234  *
 235  * \return The task list.
 236  *
 237  * Each entry of the list contains an identifier which is simply a hex number.
 238  * The result is dynamically allocated and must be freed by the caller.
 239  */
 240 char *get_task_list(void)
 241 {
 242         struct task *t, *tmp;
 243         char *msg = NULL;
 244
 245         if (!initialized)
 246                 return NULL;
 247         list_for_each_entry_safe(t, tmp, &pre_select_list, pre_select_node) {
 248                 char *tmp_msg;
 249                 tmp_msg = make_message("%s%p\tpre\t%s\n", msg? msg : "", t, t->status);
 250                 free(msg);
 251                 msg = tmp_msg;
 252         }
 253         list_for_each_entry_safe(t, tmp, &post_select_list, post_select_node) {
 254                 char *tmp_msg;
 255 //              if (t->pre_select)
 256 //                      continue;
 257                 tmp_msg = make_message("%s%p\tpost\t%s\n", msg? msg : "", t, t->status);
 258                 free(msg);
 259                 msg = tmp_msg;
 260         }
 261         //PARA_DEBUG_LOG("task list:\n%s", msg);
 262         return msg;
 263 }
 264
 265 /**
 266  * Set the select timeout to the minimal possible value.
 267  *
 268  * \param s Pointer to the scheduler struct.
 269  *
 270  * This causes the next select() call to return immediately.
 271  */
 272 void sched_min_delay(struct sched *s)
 273 {
 274         s->select_timeout.tv_sec = s->select_timeout.tv_usec = 0;
 275 }
 276
 277 /**
 278  * Impose an upper bound for the timeout of the next select() call.
 279  *
 280  * \param to Maximal allowed timeout.
 281  * \param s Pointer to the scheduler struct.
 282  *
 283  * If the current scheduler timeout is already smaller than \a to, this
 284  * function does nothing. Otherwise the timeout for the next select() call is
 285  * set to the given value.
 286  *
 287  * \sa sched_request_timeout_ms().
 288  */
 289 void sched_request_timeout(struct timeval *to, struct sched *s)
 290 {
 291         if (tv_diff(&s->select_timeout, to, NULL) > 0)
 292                 s->select_timeout = *to;
 293 }
 294
 295 /**
 296  * Force the next select() call to return before the given amount of milliseconds.
 297  *
 298  * \param ms The maximal allowed timeout in milliseconds.
 299  * \param s Pointer to the scheduler struct.
 300  *
 301  * Like sched_request_timeout() this imposes an upper bound on the timeout
 302  * value for the next select() call.
 303  */
 304 void sched_request_timeout_ms(long unsigned ms, struct sched *s)
 305 {
 306         struct timeval tv;
 307         ms2tv(ms, &tv);
 308         sched_request_timeout(&tv, s);
 309 }
 310
 311 /**
 312  * Force the next select() call to return before the given future time.
 313  *
 314  * \param barrier Absolute time before select() should return.
 315  * \param s Pointer to the scheduler struct.
 316  *
 317  * \return If \a barrier is in the past, this function does nothing and returns
 318  * zero. Otherwise it returns one.
 319  *
 320  * \sa sched_request_barrier_or_min_delay().
 321  */
 322 int sched_request_barrier(struct timeval *barrier, struct sched *s)
 323 {
 324         struct timeval diff;
 325
 326         if (tv_diff(now, barrier, &diff) > 0)
 327                 return 0;
 328         sched_request_timeout(&diff, s);
 329         return 1;
 330 }
 331
 332 /**
 333  * Force the next select() call to return before the given 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 requests a minimal
 339  * timeout and returns zero. Otherwise it returns one.
 340  *
 341  * \sa sched_min_delay(), sched_request_barrier().
 342  */
 343 int sched_request_barrier_or_min_delay(struct timeval *barrier, struct sched *s)
 344 {
 345         struct timeval diff;
 346
 347         if (tv_diff(now, barrier, &diff) > 0) {
 348                 sched_min_delay(s);
 349                 return 0;
 350         }
 351         sched_request_timeout(&diff, s);
 352         return 1;
 353 }