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