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