resolv/gai_misc.c

   1 /* Copyright (C) 2001-2023 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include <assert.h>
  19 #include <errno.h>
  20 #include <pthread.h>
  21 #include <stdlib.h>
  22 #include <sys/time.h>
  23
  24 #include <gai_misc.h>
  25
  26 #if !PTHREAD_IN_LIBC
  27 /* The available function names differ outside of libc.  (In libc, we
  28    need to use hidden aliases to avoid the PLT.)  */
  29 #define __pthread_attr_init pthread_attr_init
  30 #define __pthread_attr_setdetachstate pthread_attr_setdetachstate
  31 #define __pthread_cond_signal pthread_cond_signal
  32 #define __pthread_cond_timedwait pthread_cond_timedwait
  33 #define __pthread_create pthread_create
  34 #define __pthread_exit pthread_exit
  35 #endif
  36
  37 #ifndef gai_create_helper_thread
  38 # define gai_create_helper_thread __gai_create_helper_thread
  39
  40 extern inline int
  41 __gai_create_helper_thread (pthread_t *threadp, void *(*tf) (void *),
  42                             void *arg)
  43 {
  44   pthread_attr_t attr;
  45
  46   /* Make sure the thread is created detached.  */
  47   __pthread_attr_init (&attr);
  48   __pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
  49
  50   int ret = __pthread_create (threadp, &attr, tf, arg);
  51
  52   (void) __pthread_attr_destroy (&attr);
  53   return ret;
  54 }
  55 #endif
  56
  57
  58 /* Pool of request list entries.  */
  59 static struct requestlist **pool;
  60
  61 /* Number of total and allocated pool entries.  */
  62 static size_t pool_max_size;
  63 static size_t pool_size;
  64
  65 /* We implement a two dimensional array but allocate each row separately.
  66    The macro below determines how many entries should be used per row.
  67    It should better be a power of two.  */
  68 #define ENTRIES_PER_ROW 32
  69
  70 /* How many rows we allocate at once.  */
  71 #define ROWS_STEP       8
  72
  73 /* List of available entries.  */
  74 static struct requestlist *freelist;
  75
  76 /* Structure list of all currently processed requests.  */
  77 static struct requestlist *requests;
  78 static struct requestlist *requests_tail;
  79
  80 /* Number of threads currently running.  */
  81 static int nthreads;
  82
  83 /* Number of threads waiting for work to arrive. */
  84 static int idle_thread_count;
  85
  86
  87 /* These are the values used for optimization.  We will probably
  88    create a function to set these values.  */
  89 static struct gaiinit optim =
  90 {
  91   20,   /* int gai_threads;     Maximal number of threads.  */
  92   64,   /* int gai_num;         Number of expected simultaneous requests. */
  93   0,
  94   0,
  95   0,
  96   0,
  97   1,
  98   0
  99 };
 100
 101
 102 /* Since the list is global we need a mutex protecting it.  */
 103 pthread_mutex_t __gai_requests_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 104
 105 /* When you add a request to the list and there are idle threads present,
 106    you signal this condition variable. When a thread finishes work, it waits
 107    on this condition variable for a time before it actually exits. */
 108 pthread_cond_t __gai_new_request_notification = PTHREAD_COND_INITIALIZER;
 109
 110
 111 /* Functions to handle request list pool.  */
 112 static struct requestlist *
 113 get_elem (void)
 114 {
 115   struct requestlist *result;
 116
 117   if (freelist == NULL)
 118     {
 119       struct requestlist *new_row;
 120       int cnt;
 121
 122       if (pool_size + 1 >= pool_max_size)
 123         {
 124           size_t new_max_size = pool_max_size + ROWS_STEP;
 125           struct requestlist **new_tab;
 126
 127           new_tab = (struct requestlist **)
 128             realloc (pool, new_max_size * sizeof (struct requestlist *));
 129
 130           if (new_tab == NULL)
 131             return NULL;
 132
 133           pool_max_size = new_max_size;
 134           pool = new_tab;
 135         }
 136
 137       /* Allocate the new row.  */
 138       cnt = pool_size == 0 ? optim.gai_num : ENTRIES_PER_ROW;
 139       new_row = (struct requestlist *) calloc (cnt,
 140                                                sizeof (struct requestlist));
 141       if (new_row == NULL)
 142         return NULL;
 143
 144       pool[pool_size++] = new_row;
 145
 146       /* Put all the new entries in the freelist.  */
 147       do
 148         {
 149           new_row->next = freelist;
 150           freelist = new_row++;
 151         }
 152       while (--cnt > 0);
 153     }
 154
 155   result = freelist;
 156   freelist = freelist->next;
 157
 158   return result;
 159 }
 160
 161
 162 struct requestlist *
 163 __gai_find_request (const struct gaicb *gaicbp)
 164 {
 165   struct requestlist *runp;
 166
 167   runp = requests;
 168   while (runp != NULL)
 169     if (runp->gaicbp == gaicbp)
 170       return runp;
 171     else
 172       runp = runp->next;
 173
 174   return NULL;
 175 }
 176
 177
 178 int
 179 __gai_remove_request (struct gaicb *gaicbp)
 180 {
 181   struct requestlist *runp;
 182   struct requestlist *lastp;
 183
 184   runp = requests;
 185   lastp = NULL;
 186   while (runp != NULL)
 187     if (runp->gaicbp == gaicbp)
 188       break;
 189     else
 190       {
 191         lastp = runp;
 192         runp = runp->next;
 193       }
 194
 195   if (runp == NULL)
 196     /* Not known.  */
 197     return -1;
 198   if (runp->running != 0)
 199     /* Currently handled.  */
 200     return 1;
 201
 202   /* Dequeue the request.  */
 203   if (lastp == NULL)
 204     requests = runp->next;
 205   else
 206     lastp->next = runp->next;
 207   if (runp == requests_tail)
 208     requests_tail = lastp;
 209
 210   return 0;
 211 }
 212
 213
 214 /* The thread handler.  */
 215 static void *handle_requests (void *arg);
 216
 217
 218 /* The main function of the async I/O handling.  It enqueues requests
 219    and if necessary starts and handles threads.  */
 220 struct requestlist *
 221 __gai_enqueue_request (struct gaicb *gaicbp)
 222 {
 223   struct requestlist *newp;
 224   struct requestlist *lastp;
 225
 226   /* Get the mutex.  */
 227   __pthread_mutex_lock (&__gai_requests_mutex);
 228
 229   /* Get a new element for the waiting list.  */
 230   newp = get_elem ();
 231   if (newp == NULL)
 232     {
 233       __pthread_mutex_unlock (&__gai_requests_mutex);
 234       __set_errno (EAGAIN);
 235       return NULL;
 236     }
 237   newp->running = 0;
 238   newp->gaicbp = gaicbp;
 239   newp->waiting = NULL;
 240   newp->next = NULL;
 241
 242   lastp = requests_tail;
 243   if (requests_tail == NULL)
 244     requests = requests_tail = newp;
 245   else
 246     {
 247       requests_tail->next = newp;
 248       requests_tail = newp;
 249     }
 250
 251   gaicbp->__return = EAI_INPROGRESS;
 252
 253   /* See if we need to and are able to create a thread.  */
 254   if (nthreads < optim.gai_threads && idle_thread_count == 0)
 255     {
 256       pthread_t thid;
 257
 258       newp->running = 1;
 259
 260       /* Now try to start a thread.  */
 261       if (gai_create_helper_thread (&thid, handle_requests, newp) == 0)
 262         /* We managed to enqueue the request.  All errors which can
 263            happen now can be recognized by calls to `gai_error'.  */
 264         ++nthreads;
 265       else
 266         {
 267           if (nthreads == 0)
 268             {
 269               /* We cannot create a thread in the moment and there is
 270                  also no thread running.  This is a problem.  `errno' is
 271                  set to EAGAIN if this is only a temporary problem.  */
 272               assert (requests == newp || lastp->next == newp);
 273               if (lastp != NULL)
 274                 lastp->next = NULL;
 275               else
 276                 requests = NULL;
 277               requests_tail = lastp;
 278
 279               newp->next = freelist;
 280               freelist = newp;
 281
 282               newp = NULL;
 283             }
 284           else
 285             /* We are not handling the request after all.  */
 286             newp->running = 0;
 287         }
 288     }
 289
 290   /* Enqueue the request in the request queue.  */
 291   if (newp != NULL)
 292     {
 293       /* If there is a thread waiting for work, then let it know that we
 294          have just given it something to do. */
 295       if (idle_thread_count > 0)
 296         __pthread_cond_signal (&__gai_new_request_notification);
 297     }
 298
 299   /* Release the mutex.  */
 300   __pthread_mutex_unlock (&__gai_requests_mutex);
 301
 302   return newp;
 303 }
 304
 305
 306 static void *
 307 __attribute__ ((noreturn))
 308 handle_requests (void *arg)
 309 {
 310   struct requestlist *runp = (struct requestlist *) arg;
 311
 312   do
 313     {
 314       /* If runp is NULL, then we were created to service the work queue
 315          in general, not to handle any particular request. In that case we
 316          skip the "do work" stuff on the first pass, and go directly to the
 317          "get work off the work queue" part of this loop, which is near the
 318          end. */
 319       if (runp == NULL)
 320         __pthread_mutex_lock (&__gai_requests_mutex);
 321       else
 322         {
 323           /* Make the request.  */
 324           struct gaicb *req = runp->gaicbp;
 325           struct requestlist *srchp;
 326           struct requestlist *lastp;
 327
 328           req->__return = getaddrinfo (req->ar_name, req->ar_service,
 329                                        req->ar_request, &req->ar_result);
 330
 331           /* Get the mutex.  */
 332           __pthread_mutex_lock (&__gai_requests_mutex);
 333
 334           /* Send the signal to notify about finished processing of the
 335              request.  */
 336           __gai_notify (runp);
 337
 338           /* Now dequeue the current request.  */
 339           lastp = NULL;
 340           srchp = requests;
 341           while (srchp != runp)
 342             {
 343               lastp = srchp;
 344               srchp = srchp->next;
 345             }
 346           assert (runp->running == 1);
 347
 348           if (requests_tail == runp)
 349             requests_tail = lastp;
 350           if (lastp == NULL)
 351             requests = requests->next;
 352           else
 353             lastp->next = runp->next;
 354
 355           /* Free the old element.  */
 356           runp->next = freelist;
 357           freelist = runp;
 358         }
 359
 360       runp = requests;
 361       while (runp != NULL && runp->running != 0)
 362         runp = runp->next;
 363
 364       /* If the runlist is empty, then we sleep for a while, waiting for
 365          something to arrive in it. */
 366       if (runp == NULL && optim.gai_idle_time >= 0)
 367         {
 368           struct timespec now;
 369           struct timespec wakeup_time;
 370
 371           ++idle_thread_count;
 372           __clock_gettime (CLOCK_REALTIME, &now);
 373           wakeup_time.tv_sec = now.tv_sec + optim.gai_idle_time;
 374           wakeup_time.tv_nsec = now.tv_nsec;
 375           if (wakeup_time.tv_nsec >= 1000000000)
 376             {
 377               wakeup_time.tv_nsec -= 1000000000;
 378               ++wakeup_time.tv_sec;
 379             }
 380           __pthread_cond_timedwait (&__gai_new_request_notification,
 381                                     &__gai_requests_mutex, &wakeup_time);
 382           --idle_thread_count;
 383           runp = requests;
 384           while (runp != NULL && runp->running != 0)
 385             runp = runp->next;
 386         }
 387
 388       if (runp == NULL)
 389         --nthreads;
 390       else
 391         {
 392           /* Mark the request as being worked on.  */
 393           assert (runp->running == 0);
 394           runp->running = 1;
 395
 396           /* If we have a request to process, and there's still another in
 397              the run list, then we need to either wake up or create a new
 398              thread to service the request that is still in the run list. */
 399           if (requests != NULL)
 400             {
 401               /* There are at least two items in the work queue to work on.
 402                  If there are other idle threads, then we should wake them
 403                  up for these other work elements; otherwise, we should try
 404                  to create a new thread. */
 405               if (idle_thread_count > 0)
 406                 __pthread_cond_signal (&__gai_new_request_notification);
 407               else if (nthreads < optim.gai_threads)
 408                 {
 409                   pthread_t thid;
 410                   pthread_attr_t attr;
 411
 412                   /* Make sure the thread is created detached.  */
 413                   __pthread_attr_init (&attr);
 414                   __pthread_attr_setdetachstate (&attr,
 415                                                  PTHREAD_CREATE_DETACHED);
 416
 417                   /* Now try to start a thread. If we fail, no big deal,
 418                      because we know that there is at least one thread (us)
 419                      that is working on lookup operations. */
 420                   if (__pthread_create (&thid, &attr, handle_requests, NULL)
 421                       == 0)
 422                     ++nthreads;
 423                 }
 424             }
 425         }
 426
 427       /* Release the mutex.  */
 428       __pthread_mutex_unlock (&__gai_requests_mutex);
 429     }
 430   while (runp != NULL);
 431
 432   __pthread_exit (NULL);
 433 }
 434
 435
 436 /* Free allocated resources.  */
 437 #if !PTHREAD_IN_LIBC
 438 __attribute__ ((__destructor__)) static
 439 #endif
 440 void
 441 __gai_freemem (void)
 442 {
 443   size_t row;
 444
 445   for (row = 0; row < pool_max_size; ++row)
 446     free (pool[row]);
 447
 448   free (pool);
 449 }