sysdeps/pthread/timer_routines.c

   1 /* Helper code for POSIX timer implementation on NPTL.
   2    Copyright (C) 2000-2018 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Kaz Kylheku <kaz@ashi.footprints.net>.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public License as
   8    published by the Free Software Foundation; either version 2.1 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If
  18    not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #include <assert.h>
  21 #include <errno.h>
  22 #include <pthread.h>
  23 #include <stddef.h>
  24 #include <stdlib.h>
  25 #include <string.h>
  26 #include <sysdep.h>
  27 #include <time.h>
  28 #include <unistd.h>
  29 #include <sys/syscall.h>
  30
  31 #include "posix-timer.h"
  32 #include <timer_routines.h>
  33
  34 #ifndef DELAYTIMER_MAX
  35 # define DELAYTIMER_MAX INT_MAX
  36 #endif
  37
  38 /* Number of threads used.  */
  39 #define THREAD_MAXNODES 16
  40
  41 /* Array containing the descriptors for the used threads.  */
  42 static struct thread_node thread_array[THREAD_MAXNODES];
  43
  44 /* Static array with the structures for all the timers.  */
  45 struct timer_node __timer_array[TIMER_MAX];
  46
  47 /* Global lock to protect operation on the lists.  */
  48 pthread_mutex_t __timer_mutex = PTHREAD_MUTEX_INITIALIZER;
  49
  50 /* Variable to protext initialization.  */
  51 pthread_once_t __timer_init_once_control = PTHREAD_ONCE_INIT;
  52
  53 /* Nonzero if initialization of timer implementation failed.  */
  54 int __timer_init_failed;
  55
  56 /* Node for the thread used to deliver signals.  */
  57 struct thread_node __timer_signal_thread_rclk;
  58
  59 /* Lists to keep free and used timers and threads.  */
  60 static struct list_head timer_free_list;
  61 static struct list_head thread_free_list;
  62 static struct list_head thread_active_list;
  63
  64
  65 #ifdef __NR_rt_sigqueueinfo
  66 extern int __syscall_rt_sigqueueinfo (int, int, siginfo_t *);
  67 #endif
  68
  69
  70 /* List handling functions.  */
  71 static inline void
  72 list_append (struct list_head *list, struct list_head *newp)
  73 {
  74   newp->prev = list->prev;
  75   newp->next = list;
  76   list->prev->next = newp;
  77   list->prev = newp;
  78 }
  79
  80 static inline void
  81 list_insbefore (struct list_head *list, struct list_head *newp)
  82 {
  83   list_append (list, newp);
  84 }
  85
  86 /*
  87  * Like list_unlink_ip, except that calling it on a node that
  88  * is already unlinked is disastrous rather than a noop.
  89  */
  90
  91 static inline void
  92 list_unlink (struct list_head *list)
  93 {
  94   struct list_head *lnext = list->next, *lprev = list->prev;
  95
  96   lnext->prev = lprev;
  97   lprev->next = lnext;
  98 }
  99
 100 static inline struct list_head *
 101 list_first (struct list_head *list)
 102 {
 103   return list->next;
 104 }
 105
 106 static inline struct list_head *
 107 list_null (struct list_head *list)
 108 {
 109   return list;
 110 }
 111
 112 static inline struct list_head *
 113 list_next (struct list_head *list)
 114 {
 115   return list->next;
 116 }
 117
 118 static inline int
 119 list_isempty (struct list_head *list)
 120 {
 121   return list->next == list;
 122 }
 123
 124
 125 /* Functions build on top of the list functions.  */
 126 static inline struct thread_node *
 127 thread_links2ptr (struct list_head *list)
 128 {
 129   return (struct thread_node *) ((char *) list
 130                                  - offsetof (struct thread_node, links));
 131 }
 132
 133 static inline struct timer_node *
 134 timer_links2ptr (struct list_head *list)
 135 {
 136   return (struct timer_node *) ((char *) list
 137                                 - offsetof (struct timer_node, links));
 138 }
 139
 140
 141 /* Initialize a newly allocated thread structure.  */
 142 static void
 143 thread_init (struct thread_node *thread, const pthread_attr_t *attr, clockid_t clock_id)
 144 {
 145   if (attr != NULL)
 146     thread->attr = *attr;
 147   else
 148     {
 149       pthread_attr_init (&thread->attr);
 150       pthread_attr_setdetachstate (&thread->attr, PTHREAD_CREATE_DETACHED);
 151     }
 152
 153   thread->exists = 0;
 154   INIT_LIST_HEAD (&thread->timer_queue);
 155   pthread_cond_init (&thread->cond, 0);
 156   thread->current_timer = 0;
 157   thread->captured = pthread_self ();
 158   thread->clock_id = clock_id;
 159 }
 160
 161
 162 /* Initialize the global lists, and acquire global resources.  Error
 163    reporting is done by storing a non-zero value to the global variable
 164    timer_init_failed.  */
 165 static void
 166 init_module (void)
 167 {
 168   int i;
 169
 170   INIT_LIST_HEAD (&timer_free_list);
 171   INIT_LIST_HEAD (&thread_free_list);
 172   INIT_LIST_HEAD (&thread_active_list);
 173
 174   for (i = 0; i < TIMER_MAX; ++i)
 175     {
 176       list_append (&timer_free_list, &__timer_array[i].links);
 177       __timer_array[i].inuse = TIMER_FREE;
 178     }
 179
 180   for (i = 0; i < THREAD_MAXNODES; ++i)
 181     list_append (&thread_free_list, &thread_array[i].links);
 182
 183   thread_init (&__timer_signal_thread_rclk, 0, CLOCK_REALTIME);
 184 }
 185
 186
 187 /* This is a handler executed in a child process after a fork()
 188    occurs.  It reinitializes the module, resetting all of the data
 189    structures to their initial state.  The mutex is initialized in
 190    case it was locked in the parent process.  */
 191 static void
 192 reinit_after_fork (void)
 193 {
 194   init_module ();
 195   pthread_mutex_init (&__timer_mutex, 0);
 196 }
 197
 198
 199 /* Called once form pthread_once in timer_init. This initializes the
 200    module and ensures that reinit_after_fork will be executed in any
 201    child process.  */
 202 void
 203 __timer_init_once (void)
 204 {
 205   init_module ();
 206   pthread_atfork (0, 0, reinit_after_fork);
 207 }
 208
 209
 210 /* Deinitialize a thread that is about to be deallocated.  */
 211 static void
 212 thread_deinit (struct thread_node *thread)
 213 {
 214   assert (list_isempty (&thread->timer_queue));
 215   pthread_cond_destroy (&thread->cond);
 216 }
 217
 218
 219 /* Allocate a thread structure from the global free list.  Global
 220    mutex lock must be held by caller.  The thread is moved to
 221    the active list. */
 222 struct thread_node *
 223 __timer_thread_alloc (const pthread_attr_t *desired_attr, clockid_t clock_id)
 224 {
 225   struct list_head *node = list_first (&thread_free_list);
 226
 227   if (node != list_null (&thread_free_list))
 228     {
 229       struct thread_node *thread = thread_links2ptr (node);
 230       list_unlink (node);
 231       thread_init (thread, desired_attr, clock_id);
 232       list_append (&thread_active_list, node);
 233       return thread;
 234     }
 235
 236   return 0;
 237 }
 238
 239
 240 /* Return a thread structure to the global free list.  Global lock
 241    must be held by caller.  */
 242 void
 243 __timer_thread_dealloc (struct thread_node *thread)
 244 {
 245   thread_deinit (thread);
 246   list_unlink (&thread->links);
 247   list_append (&thread_free_list, &thread->links);
 248 }
 249
 250
 251 /* Each of our threads which terminates executes this cleanup
 252    handler. We never terminate threads ourselves; if a thread gets here
 253    it means that the evil application has killed it.  If the thread has
 254    timers, these require servicing and so we must hire a replacement
 255    thread right away.  We must also unblock another thread that may
 256    have been waiting for this thread to finish servicing a timer (see
 257    timer_delete()).  */
 258
 259 static void
 260 thread_cleanup (void *val)
 261 {
 262   if (val != NULL)
 263     {
 264       struct thread_node *thread = val;
 265
 266       /* How did the signal thread get killed?  */
 267       assert (thread != &__timer_signal_thread_rclk);
 268
 269       pthread_mutex_lock (&__timer_mutex);
 270
 271       thread->exists = 0;
 272
 273       /* We are no longer processing a timer event.  */
 274       thread->current_timer = 0;
 275
 276       if (list_isempty (&thread->timer_queue))
 277         __timer_thread_dealloc (thread);
 278       else
 279         (void) __timer_thread_start (thread);
 280
 281       pthread_mutex_unlock (&__timer_mutex);
 282
 283       /* Unblock potentially blocked timer_delete().  */
 284       pthread_cond_broadcast (&thread->cond);
 285     }
 286 }
 287
 288
 289 /* Handle a timer which is supposed to go off now.  */
 290 static void
 291 thread_expire_timer (struct thread_node *self, struct timer_node *timer)
 292 {
 293   self->current_timer = timer; /* Lets timer_delete know timer is running. */
 294
 295   pthread_mutex_unlock (&__timer_mutex);
 296
 297   switch (__builtin_expect (timer->event.sigev_notify, SIGEV_SIGNAL))
 298     {
 299     case SIGEV_NONE:
 300       break;
 301
 302     case SIGEV_SIGNAL:
 303 #ifdef __NR_rt_sigqueueinfo
 304       {
 305         siginfo_t info;
 306
 307         /* First, clear the siginfo_t structure, so that we don't pass our
 308            stack content to other tasks.  */
 309         memset (&info, 0, sizeof (siginfo_t));
 310         /* We must pass the information about the data in a siginfo_t
 311            value.  */
 312         info.si_signo = timer->event.sigev_signo;
 313         info.si_code = SI_TIMER;
 314         info.si_pid = timer->creator_pid;
 315         info.si_uid = getuid ();
 316         info.si_value = timer->event.sigev_value;
 317
 318         INLINE_SYSCALL (rt_sigqueueinfo, 3, info.si_pid, info.si_signo, &info);
 319       }
 320 #else
 321       if (pthread_kill (self->captured, timer->event.sigev_signo) != 0)
 322         {
 323           if (pthread_kill (self->id, timer->event.sigev_signo) != 0)
 324             abort ();
 325         }
 326 #endif
 327       break;
 328
 329     case SIGEV_THREAD:
 330       timer->event.sigev_notify_function (timer->event.sigev_value);
 331       break;
 332
 333     default:
 334       assert (! "unknown event");
 335       break;
 336     }
 337
 338   pthread_mutex_lock (&__timer_mutex);
 339
 340   self->current_timer = 0;
 341
 342   pthread_cond_broadcast (&self->cond);
 343 }
 344
 345
 346 /* Thread function; executed by each timer thread. The job of this
 347    function is to wait on the thread's timer queue and expire the
 348    timers in chronological order as close to their scheduled time as
 349    possible.  */
 350 static void
 351 __attribute__ ((noreturn))
 352 thread_func (void *arg)
 353 {
 354   struct thread_node *self = arg;
 355
 356   /* Register cleanup handler, in case rogue application terminates
 357      this thread.  (This cannot happen to __timer_signal_thread, which
 358      doesn't invoke application callbacks). */
 359
 360   pthread_cleanup_push (thread_cleanup, self);
 361
 362   pthread_mutex_lock (&__timer_mutex);
 363
 364   while (1)
 365     {
 366       struct list_head *first;
 367       struct timer_node *timer = NULL;
 368
 369       /* While the timer queue is not empty, inspect the first node.  */
 370       first = list_first (&self->timer_queue);
 371       if (first != list_null (&self->timer_queue))
 372         {
 373           struct timespec now;
 374
 375           timer = timer_links2ptr (first);
 376
 377           /* This assumes that the elements of the list of one thread
 378              are all for the same clock.  */
 379           clock_gettime (timer->clock, &now);
 380
 381           while (1)
 382             {
 383               /* If the timer is due or overdue, remove it from the queue.
 384                  If it's a periodic timer, re-compute its new time and
 385                  requeue it.  Either way, perform the timer expiry. */
 386               if (timespec_compare (&now, &timer->expirytime) < 0)
 387                 break;
 388
 389               list_unlink_ip (first);
 390
 391               if (__builtin_expect (timer->value.it_interval.tv_sec, 0) != 0
 392                   || timer->value.it_interval.tv_nsec != 0)
 393                 {
 394                   timer->overrun_count = 0;
 395                   timespec_add (&timer->expirytime, &timer->expirytime,
 396                                 &timer->value.it_interval);
 397                   while (timespec_compare (&timer->expirytime, &now) < 0)
 398                     {
 399                       timespec_add (&timer->expirytime, &timer->expirytime,
 400                                     &timer->value.it_interval);
 401                       if (timer->overrun_count < DELAYTIMER_MAX)
 402                         ++timer->overrun_count;
 403                     }
 404                   __timer_thread_queue_timer (self, timer);
 405                 }
 406
 407               thread_expire_timer (self, timer);
 408
 409               first = list_first (&self->timer_queue);
 410               if (first == list_null (&self->timer_queue))
 411                 break;
 412
 413               timer = timer_links2ptr (first);
 414             }
 415         }
 416
 417       /* If the queue is not empty, wait until the expiry time of the
 418          first node.  Otherwise wait indefinitely.  Insertions at the
 419          head of the queue must wake up the thread by broadcasting
 420          this condition variable.  */
 421       if (timer != NULL)
 422         pthread_cond_timedwait (&self->cond, &__timer_mutex,
 423                                 &timer->expirytime);
 424       else
 425         pthread_cond_wait (&self->cond, &__timer_mutex);
 426     }
 427   /* This macro will never be executed since the while loop loops
 428      forever - but we have to add it for proper nesting.  */
 429   pthread_cleanup_pop (1);
 430 }
 431
 432
 433 /* Enqueue a timer in wakeup order in the thread's timer queue.
 434    Returns 1 if the timer was inserted at the head of the queue,
 435    causing the queue's next wakeup time to change. */
 436
 437 int
 438 __timer_thread_queue_timer (struct thread_node *thread,
 439                             struct timer_node *insert)
 440 {
 441   struct list_head *iter;
 442   int athead = 1;
 443
 444   for (iter = list_first (&thread->timer_queue);
 445        iter != list_null (&thread->timer_queue);
 446         iter = list_next (iter))
 447     {
 448       struct timer_node *timer = timer_links2ptr (iter);
 449
 450       if (timespec_compare (&insert->expirytime, &timer->expirytime) < 0)
 451           break;
 452       athead = 0;
 453     }
 454
 455   list_insbefore (iter, &insert->links);
 456   return athead;
 457 }
 458
 459
 460 /* Start a thread and associate it with the given thread node.  Global
 461    lock must be held by caller.  */
 462 int
 463 __timer_thread_start (struct thread_node *thread)
 464 {
 465   int retval = 1;
 466
 467   assert (!thread->exists);
 468   thread->exists = 1;
 469
 470   if (pthread_create (&thread->id, &thread->attr,
 471                       (void *(*) (void *)) thread_func, thread) != 0)
 472     {
 473       thread->exists = 0;
 474       retval = -1;
 475     }
 476
 477   return retval;
 478 }
 479
 480
 481 void
 482 __timer_thread_wakeup (struct thread_node *thread)
 483 {
 484   pthread_cond_broadcast (&thread->cond);
 485 }
 486
 487
 488
 489 /* Search the list of active threads and find one which has matching
 490    attributes.  Global mutex lock must be held by caller.  */
 491 struct thread_node *
 492 __timer_thread_find_matching (const pthread_attr_t *desired_attr,
 493                               clockid_t desired_clock_id)
 494 {
 495   struct list_head *iter = list_first (&thread_active_list);
 496
 497   while (iter != list_null (&thread_active_list))
 498     {
 499       struct thread_node *candidate = thread_links2ptr (iter);
 500
 501       if (thread_attr_compare (desired_attr, &candidate->attr)
 502           && desired_clock_id == candidate->clock_id)
 503         return candidate;
 504
 505       iter = list_next (iter);
 506     }
 507
 508   return NULL;
 509 }
 510
 511
 512 /* Grab a free timer structure from the global free list.  The global
 513    lock must be held by the caller.  */
 514 struct timer_node *
 515 __timer_alloc (void)
 516 {
 517   struct list_head *node = list_first (&timer_free_list);
 518
 519   if (node != list_null (&timer_free_list))
 520     {
 521       struct timer_node *timer = timer_links2ptr (node);
 522       list_unlink_ip (node);
 523       timer->inuse = TIMER_INUSE;
 524       timer->refcount = 1;
 525       return timer;
 526     }
 527
 528   return NULL;
 529 }
 530
 531
 532 /* Return a timer structure to the global free list.  The global lock
 533    must be held by the caller.  */
 534 void
 535 __timer_dealloc (struct timer_node *timer)
 536 {
 537   assert (timer->refcount == 0);
 538   timer->thread = NULL; /* Break association between timer and thread.  */
 539   timer->inuse = TIMER_FREE;
 540   list_append (&timer_free_list, &timer->links);
 541 }
 542
 543
 544 /* Thread cancellation handler which unlocks a mutex.  */
 545 void
 546 __timer_mutex_cancel_handler (void *arg)
 547 {
 548   pthread_mutex_unlock (arg);
 549 }