resolv/gai_misc.c

   1 /* Copyright (C) 2001-2021 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 2001.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <assert.h>
  20 #include <errno.h>
  21 #include <pthread.h>
  22 #include <stdlib.h>
  23 #include <sys/time.h>
  24
  25 #include <gai_misc.h>
  26
  27 #if !PTHREAD_IN_LIBC
  28 /* The available function names differ outside of libc.  (In libc, we
  29    need to use hidden aliases to avoid the PLT.)  */
  30 #define __pthread_attr_init pthread_attr_init
  31 #define __pthread_attr_setdetachstate pthread_attr_setdetachstate
  32 #define __pthread_cond_signal pthread_cond_signal
  33 #define __pthread_cond_timedwait pthread_cond_timedwait
  34 #define __pthread_create pthread_create
  35 #define __pthread_exit pthread_exit
  36 #endif
  37
  38 #ifndef gai_create_helper_thread
  39 # define gai_create_helper_thread __gai_create_helper_thread
  40
  41 extern inline int
  42 __gai_create_helper_thread (pthread_t *threadp, void *(*tf) (void *),
  43                             void *arg)
  44 {
  45   pthread_attr_t attr;
  46
  47   /* Make sure the thread is created detached.  */
  48   __pthread_attr_init (&attr);
  49   __pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
  50
  51   int ret = __pthread_create (threadp, &attr, tf, arg);
  52
  53   (void) __pthread_attr_destroy (&attr);
  54   return ret;
  55 }
  56 #endif
  57
  58
  59 /* Pool of request list entries.  */
  60 static struct requestlist **pool;
  61
  62 /* Number of total and allocated pool entries.  */
  63 static size_t pool_max_size;
  64 static size_t pool_size;
  65
  66 /* We implement a two dimensional array but allocate each row separately.
  67    The macro below determines how many entries should be used per row.
  68    It should better be a power of two.  */
  69 #define ENTRIES_PER_ROW 32
  70
  71 /* How many rows we allocate at once.  */
  72 #define ROWS_STEP       8
  73
  74 /* List of available entries.  */
  75 static struct requestlist *freelist;
  76
  77 /* Structure list of all currently processed requests.  */
  78 static struct requestlist *requests;
  79 static struct requestlist *requests_tail;
  80
  81 /* Number of threads currently running.  */
  82 static int nthreads;
  83
  84 /* Number of threads waiting for work to arrive. */
  85 static int idle_thread_count;
  86
  87
  88 /* These are the values used for optimization.  We will probably
  89    create a funcion to set these values.  */
  90 static struct gaiinit optim =
  91 {
  92   20,   /* int gai_threads;     Maximal number of threads.  */
  93   64,   /* int gai_num;         Number of expected simultanious requests. */
  94   0,
  95   0,
  96   0,
  97   0,
  98   1,
  99   0
 100 };
 101
 102
 103 /* Since the list is global we need a mutex protecting it.  */
 104 pthread_mutex_t __gai_requests_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
 105
 106 /* When you add a request to the list and there are idle threads present,
 107    you signal this condition variable. When a thread finishes work, it waits
 108    on this condition variable for a time before it actually exits. */
 109 pthread_cond_t __gai_new_request_notification = PTHREAD_COND_INITIALIZER;
 110
 111
 112 /* Functions to handle request list pool.  */
 113 static struct requestlist *
 114 get_elem (void)
 115 {
 116   struct requestlist *result;
 117
 118   if (freelist == NULL)
 119     {
 120       struct requestlist *new_row;
 121       int cnt;
 122
 123       if (pool_size + 1 >= pool_max_size)
 124         {
 125           size_t new_max_size = pool_max_size + ROWS_STEP;
 126           struct requestlist **new_tab;
 127
 128           new_tab = (struct requestlist **)
 129             realloc (pool, new_max_size * sizeof (struct requestlist *));
 130
 131           if (new_tab == NULL)
 132             return NULL;
 133
 134           pool_max_size = new_max_size;
 135           pool = new_tab;
 136         }
 137
 138       /* Allocate the new row.  */
 139       cnt = pool_size == 0 ? optim.gai_num : ENTRIES_PER_ROW;
 140       new_row = (struct requestlist *) calloc (cnt,
 141                                                sizeof (struct requestlist));
 142       if (new_row == NULL)
 143         return NULL;
 144
 145       pool[pool_size++] = new_row;
 146
 147       /* Put all the new entries in the freelist.  */
 148       do
 149         {
 150           new_row->next = freelist;
 151           freelist = new_row++;
 152         }
 153       while (--cnt > 0);
 154     }
 155
 156   result = freelist;
 157   freelist = freelist->next;
 158
 159   return result;
 160 }
 161
 162
 163 struct requestlist *
 164 __gai_find_request (const struct gaicb *gaicbp)
 165 {
 166   struct requestlist *runp;
 167
 168   runp = requests;
 169   while (runp != NULL)
 170     if (runp->gaicbp == gaicbp)
 171       return runp;
 172     else
 173       runp = runp->next;
 174
 175   return NULL;
 176 }
 177
 178
 179 int
 180 __gai_remove_request (struct gaicb *gaicbp)
 181 {
 182   struct requestlist *runp;
 183   struct requestlist *lastp;
 184
 185   runp = requests;
 186   lastp = NULL;
 187   while (runp != NULL)
 188     if (runp->gaicbp == gaicbp)
 189       break;
 190     else
 191       {
 192         lastp = runp;
 193         runp = runp->next;
 194       }
 195
 196   if (runp == NULL)
 197     /* Not known.  */
 198     return -1;
 199   if (runp->running != 0)
 200     /* Currently handled.  */
 201     return 1;
 202
 203   /* Dequeue the request.  */
 204   if (lastp == NULL)
 205     requests = runp->next;
 206   else
 207     lastp->next = runp->next;
 208   if (runp == requests_tail)
 209     requests_tail = lastp;
 210
 211   return 0;
 212 }
 213
 214
 215 /* The thread handler.  */
 216 static void *handle_requests (void *arg);
 217
 218
 219 /* The main function of the async I/O handling.  It enqueues requests
 220    and if necessary starts and handles threads.  */
 221 struct requestlist *
 222 __gai_enqueue_request (struct gaicb *gaicbp)
 223 {
 224   struct requestlist *newp;
 225   struct requestlist *lastp;
 226
 227   /* Get the mutex.  */
 228   __pthread_mutex_lock (&__gai_requests_mutex);
 229
 230   /* Get a new element for the waiting list.  */
 231   newp = get_elem ();
 232   if (newp == NULL)
 233     {
 234       __pthread_mutex_unlock (&__gai_requests_mutex);
 235       __set_errno (EAGAIN);
 236       return NULL;
 237     }
 238   newp->running = 0;
 239   newp->gaicbp = gaicbp;
 240   newp->waiting = NULL;
 241   newp->next = NULL;
 242
 243   lastp = requests_tail;
 244   if (requests_tail == NULL)
 245     requests = requests_tail = newp;
 246   else
 247     {
 248       requests_tail->next = newp;
 249       requests_tail = newp;
 250     }
 251
 252   gaicbp->__return = EAI_INPROGRESS;
 253
 254   /* See if we need to and are able to create a thread.  */
 255   if (nthreads < optim.gai_threads && idle_thread_count == 0)
 256     {
 257       pthread_t thid;
 258
 259       newp->running = 1;
 260
 261       /* Now try to start a thread.  */
 262       if (gai_create_helper_thread (&thid, handle_requests, newp) == 0)
 263         /* We managed to enqueue the request.  All errors which can
 264            happen now can be recognized by calls to `gai_error'.  */
 265         ++nthreads;
 266       else
 267         {
 268           if (nthreads == 0)
 269             {
 270               /* We cannot create a thread in the moment and there is
 271                  also no thread running.  This is a problem.  `errno' is
 272                  set to EAGAIN if this is only a temporary problem.  */
 273               assert (requests == newp || lastp->next == newp);
 274               if (lastp != NULL)
 275                 lastp->next = NULL;
 276               else
 277                 requests = NULL;
 278               requests_tail = lastp;
 279
 280               newp->next = freelist;
 281               freelist = newp;
 282
 283               newp = NULL;
 284             }
 285           else
 286             /* We are not handling the request after all.  */
 287             newp->running = 0;
 288         }
 289     }
 290
 291   /* Enqueue the request in the request queue.  */
 292   if (newp != NULL)
 293     {
 294       /* If there is a thread waiting for work, then let it know that we
 295          have just given it something to do. */
 296       if (idle_thread_count > 0)
 297         __pthread_cond_signal (&__gai_new_request_notification);
 298     }
 299
 300   /* Release the mutex.  */
 301   __pthread_mutex_unlock (&__gai_requests_mutex);
 302
 303   return newp;
 304 }
 305
 306
 307 static void *
 308 __attribute__ ((noreturn))
 309 handle_requests (void *arg)
 310 {
 311   struct requestlist *runp = (struct requestlist *) arg;
 312
 313   do
 314     {
 315       /* If runp is NULL, then we were created to service the work queue
 316          in general, not to handle any particular request. In that case we
 317          skip the "do work" stuff on the first pass, and go directly to the
 318          "get work off the work queue" part of this loop, which is near the
 319          end. */
 320       if (runp == NULL)
 321         __pthread_mutex_lock (&__gai_requests_mutex);
 322       else
 323         {
 324           /* Make the request.  */
 325           struct gaicb *req = runp->gaicbp;
 326           struct requestlist *srchp;
 327           struct requestlist *lastp;
 328
 329           req->__return = getaddrinfo (req->ar_name, req->ar_service,
 330                                        req->ar_request, &req->ar_result);
 331
 332           /* Get the mutex.  */
 333           __pthread_mutex_lock (&__gai_requests_mutex);
 334
 335           /* Send the signal to notify about finished processing of the
 336              request.  */
 337           __gai_notify (runp);
 338
 339           /* Now dequeue the current request.  */
 340           lastp = NULL;
 341           srchp = requests;
 342           while (srchp != runp)
 343             {
 344               lastp = srchp;
 345               srchp = srchp->next;
 346             }
 347           assert (runp->running == 1);
 348
 349           if (requests_tail == runp)
 350             requests_tail = lastp;
 351           if (lastp == NULL)
 352             requests = requests->next;
 353           else
 354             lastp->next = runp->next;
 355
 356           /* Free the old element.  */
 357           runp->next = freelist;
 358           freelist = runp;
 359         }
 360
 361       runp = requests;
 362       while (runp != NULL && runp->running != 0)
 363         runp = runp->next;
 364
 365       /* If the runlist is empty, then we sleep for a while, waiting for
 366          something to arrive in it. */
 367       if (runp == NULL && optim.gai_idle_time >= 0)
 368         {
 369           struct timespec now;
 370           struct timespec wakeup_time;
 371
 372           ++idle_thread_count;
 373           __clock_gettime (CLOCK_REALTIME, &now);
 374           wakeup_time.tv_sec = now.tv_sec + optim.gai_idle_time;
 375           wakeup_time.tv_nsec = now.tv_nsec;
 376           if (wakeup_time.tv_nsec >= 1000000000)
 377             {
 378               wakeup_time.tv_nsec -= 1000000000;
 379               ++wakeup_time.tv_sec;
 380             }
 381           __pthread_cond_timedwait (&__gai_new_request_notification,
 382                                     &__gai_requests_mutex, &wakeup_time);
 383           --idle_thread_count;
 384           runp = requests;
 385           while (runp != NULL && runp->running != 0)
 386             runp = runp->next;
 387         }
 388
 389       if (runp == NULL)
 390         --nthreads;
 391       else
 392         {
 393           /* Mark the request as being worked on.  */
 394           assert (runp->running == 0);
 395           runp->running = 1;
 396
 397           /* If we have a request to process, and there's still another in
 398              the run list, then we need to either wake up or create a new
 399              thread to service the request that is still in the run list. */
 400           if (requests != NULL)
 401             {
 402               /* There are at least two items in the work queue to work on.
 403                  If there are other idle threads, then we should wake them
 404                  up for these other work elements; otherwise, we should try
 405                  to create a new thread. */
 406               if (idle_thread_count > 0)
 407                 __pthread_cond_signal (&__gai_new_request_notification);
 408               else if (nthreads < optim.gai_threads)
 409                 {
 410                   pthread_t thid;
 411                   pthread_attr_t attr;
 412
 413                   /* Make sure the thread is created detached.  */
 414                   __pthread_attr_init (&attr);
 415                   __pthread_attr_setdetachstate (&attr,
 416                                                  PTHREAD_CREATE_DETACHED);
 417
 418                   /* Now try to start a thread. If we fail, no big deal,
 419                      because we know that there is at least one thread (us)
 420                      that is working on lookup operations. */
 421                   if (__pthread_create (&thid, &attr, handle_requests, NULL)
 422                       == 0)
 423                     ++nthreads;
 424                 }
 425             }
 426         }
 427
 428       /* Release the mutex.  */
 429       __pthread_mutex_unlock (&__gai_requests_mutex);
 430     }
 431   while (runp != NULL);
 432
 433   __pthread_exit (NULL);
 434 }
 435
 436
 437 /* Free allocated resources.  */
 438 libc_freeres_fn (free_res)
 439 {
 440   size_t row;
 441
 442   for (row = 0; row < pool_max_size; ++row)
 443     free (pool[row]);
 444
 445   free (pool);
 446 }