resolv/gai_misc.c

   1 /* Copyright (C) 2001-2017 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    <http://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
  28
  29 #ifndef gai_create_helper_thread
  30 # define gai_create_helper_thread __gai_create_helper_thread
  31
  32 extern inline int
  33 __gai_create_helper_thread (pthread_t *threadp, void *(*tf) (void *),
  34                             void *arg)
  35 {
  36   pthread_attr_t attr;
  37
  38   /* Make sure the thread is created detached.  */
  39   pthread_attr_init (&attr);
  40   pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
  41
  42   int ret = pthread_create (threadp, &attr, tf, arg);
  43
  44   (void) pthread_attr_destroy (&attr);
  45   return ret;
  46 }
  47 #endif
  48
  49
  50 /* Pool of request list entries.  */
  51 static struct requestlist **pool;
  52
  53 /* Number of total and allocated pool entries.  */
  54 static size_t pool_max_size;
  55 static size_t pool_size;
  56
  57 /* We implement a two dimensional array but allocate each row separately.
  58    The macro below determines how many entries should be used per row.
  59    It should better be a power of two.  */
  60 #define ENTRIES_PER_ROW 32
  61
  62 /* How many rows we allocate at once.  */
  63 #define ROWS_STEP       8
  64
  65 /* List of available entries.  */
  66 static struct requestlist *freelist;
  67
  68 /* Structure list of all currently processed requests.  */
  69 static struct requestlist *requests;
  70 static struct requestlist *requests_tail;
  71
  72 /* Number of threads currently running.  */
  73 static int nthreads;
  74
  75 /* Number of threads waiting for work to arrive. */
  76 static int idle_thread_count;
  77
  78
  79 /* These are the values used for optimization.  We will probably
  80    create a funcion to set these values.  */
  81 static struct gaiinit optim =
  82 {
  83   20,   /* int gai_threads;     Maximal number of threads.  */
  84   64,   /* int gai_num;         Number of expected simultanious requests. */
  85   0,
  86   0,
  87   0,
  88   0,
  89   1,
  90   0
  91 };
  92
  93
  94 /* Since the list is global we need a mutex protecting it.  */
  95 pthread_mutex_t __gai_requests_mutex = PTHREAD_RECURSIVE_MUTEX_INITIALIZER_NP;
  96
  97 /* When you add a request to the list and there are idle threads present,
  98    you signal this condition variable. When a thread finishes work, it waits
  99    on this condition variable for a time before it actually exits. */
 100 pthread_cond_t __gai_new_request_notification = PTHREAD_COND_INITIALIZER;
 101
 102
 103 /* Functions to handle request list pool.  */
 104 static struct requestlist *
 105 get_elem (void)
 106 {
 107   struct requestlist *result;
 108
 109   if (freelist == NULL)
 110     {
 111       struct requestlist *new_row;
 112       int cnt;
 113
 114       if (pool_size + 1 >= pool_max_size)
 115         {
 116           size_t new_max_size = pool_max_size + ROWS_STEP;
 117           struct requestlist **new_tab;
 118
 119           new_tab = (struct requestlist **)
 120             realloc (pool, new_max_size * sizeof (struct requestlist *));
 121
 122           if (new_tab == NULL)
 123             return NULL;
 124
 125           pool_max_size = new_max_size;
 126           pool = new_tab;
 127         }
 128
 129       /* Allocate the new row.  */
 130       cnt = pool_size == 0 ? optim.gai_num : ENTRIES_PER_ROW;
 131       new_row = (struct requestlist *) calloc (cnt,
 132                                                sizeof (struct requestlist));
 133       if (new_row == NULL)
 134         return NULL;
 135
 136       pool[pool_size++] = new_row;
 137
 138       /* Put all the new entries in the freelist.  */
 139       do
 140         {
 141           new_row->next = freelist;
 142           freelist = new_row++;
 143         }
 144       while (--cnt > 0);
 145     }
 146
 147   result = freelist;
 148   freelist = freelist->next;
 149
 150   return result;
 151 }
 152
 153
 154 struct requestlist *
 155 __gai_find_request (const struct gaicb *gaicbp)
 156 {
 157   struct requestlist *runp;
 158
 159   runp = requests;
 160   while (runp != NULL)
 161     if (runp->gaicbp == gaicbp)
 162       return runp;
 163     else
 164       runp = runp->next;
 165
 166   return NULL;
 167 }
 168
 169
 170 int
 171 __gai_remove_request (struct gaicb *gaicbp)
 172 {
 173   struct requestlist *runp;
 174   struct requestlist *lastp;
 175
 176   runp = requests;
 177   lastp = NULL;
 178   while (runp != NULL)
 179     if (runp->gaicbp == gaicbp)
 180       break;
 181     else
 182       {
 183         lastp = runp;
 184         runp = runp->next;
 185       }
 186
 187   if (runp == NULL)
 188     /* Not known.  */
 189     return -1;
 190   if (runp->running != 0)
 191     /* Currently handled.  */
 192     return 1;
 193
 194   /* Dequeue the request.  */
 195   if (lastp == NULL)
 196     requests = runp->next;
 197   else
 198     lastp->next = runp->next;
 199   if (runp == requests_tail)
 200     requests_tail = lastp;
 201
 202   return 0;
 203 }
 204
 205
 206 /* The thread handler.  */
 207 static void *handle_requests (void *arg);
 208
 209
 210 /* The main function of the async I/O handling.  It enqueues requests
 211    and if necessary starts and handles threads.  */
 212 struct requestlist *
 213 __gai_enqueue_request (struct gaicb *gaicbp)
 214 {
 215   struct requestlist *newp;
 216   struct requestlist *lastp;
 217
 218   /* Get the mutex.  */
 219   pthread_mutex_lock (&__gai_requests_mutex);
 220
 221   /* Get a new element for the waiting list.  */
 222   newp = get_elem ();
 223   if (newp == NULL)
 224     {
 225       pthread_mutex_unlock (&__gai_requests_mutex);
 226       __set_errno (EAGAIN);
 227       return NULL;
 228     }
 229   newp->running = 0;
 230   newp->gaicbp = gaicbp;
 231   newp->waiting = NULL;
 232   newp->next = NULL;
 233
 234   lastp = requests_tail;
 235   if (requests_tail == NULL)
 236     requests = requests_tail = newp;
 237   else
 238     {
 239       requests_tail->next = newp;
 240       requests_tail = newp;
 241     }
 242
 243   gaicbp->__return = EAI_INPROGRESS;
 244
 245   /* See if we need to and are able to create a thread.  */
 246   if (nthreads < optim.gai_threads && idle_thread_count == 0)
 247     {
 248       pthread_t thid;
 249
 250       newp->running = 1;
 251
 252       /* Now try to start a thread.  */
 253       if (gai_create_helper_thread (&thid, handle_requests, newp) == 0)
 254         /* We managed to enqueue the request.  All errors which can
 255            happen now can be recognized by calls to `gai_error'.  */
 256         ++nthreads;
 257       else
 258         {
 259           if (nthreads == 0)
 260             {
 261               /* We cannot create a thread in the moment and there is
 262                  also no thread running.  This is a problem.  `errno' is
 263                  set to EAGAIN if this is only a temporary problem.  */
 264               assert (lastp->next == newp);
 265               lastp->next = NULL;
 266               requests_tail = lastp;
 267
 268               newp->next = freelist;
 269               freelist = newp;
 270
 271               newp = NULL;
 272             }
 273           else
 274             /* We are not handling the request after all.  */
 275             newp->running = 0;
 276         }
 277     }
 278
 279   /* Enqueue the request in the request queue.  */
 280   if (newp != NULL)
 281     {
 282       /* If there is a thread waiting for work, then let it know that we
 283          have just given it something to do. */
 284       if (idle_thread_count > 0)
 285         pthread_cond_signal (&__gai_new_request_notification);
 286     }
 287
 288   /* Release the mutex.  */
 289   pthread_mutex_unlock (&__gai_requests_mutex);
 290
 291   return newp;
 292 }
 293
 294
 295 static void *
 296 __attribute__ ((noreturn))
 297 handle_requests (void *arg)
 298 {
 299   struct requestlist *runp = (struct requestlist *) arg;
 300
 301   do
 302     {
 303       /* If runp is NULL, then we were created to service the work queue
 304          in general, not to handle any particular request. In that case we
 305          skip the "do work" stuff on the first pass, and go directly to the
 306          "get work off the work queue" part of this loop, which is near the
 307          end. */
 308       if (runp == NULL)
 309         pthread_mutex_lock (&__gai_requests_mutex);
 310       else
 311         {
 312           /* Make the request.  */
 313           struct gaicb *req = runp->gaicbp;
 314           struct requestlist *srchp;
 315           struct requestlist *lastp;
 316
 317           req->__return = getaddrinfo (req->ar_name, req->ar_service,
 318                                        req->ar_request, &req->ar_result);
 319
 320           /* Get the mutex.  */
 321           pthread_mutex_lock (&__gai_requests_mutex);
 322
 323           /* Send the signal to notify about finished processing of the
 324              request.  */
 325           __gai_notify (runp);
 326
 327           /* Now dequeue the current request.  */
 328           lastp = NULL;
 329           srchp = requests;
 330           while (srchp != runp)
 331             {
 332               lastp = srchp;
 333               srchp = srchp->next;
 334             }
 335           assert (runp->running == 1);
 336
 337           if (requests_tail == runp)
 338             requests_tail = lastp;
 339           if (lastp == NULL)
 340             requests = requests->next;
 341           else
 342             lastp->next = runp->next;
 343
 344           /* Free the old element.  */
 345           runp->next = freelist;
 346           freelist = runp;
 347         }
 348
 349       runp = requests;
 350       while (runp != NULL && runp->running != 0)
 351         runp = runp->next;
 352
 353       /* If the runlist is empty, then we sleep for a while, waiting for
 354          something to arrive in it. */
 355       if (runp == NULL && optim.gai_idle_time >= 0)
 356         {
 357           struct timeval now;
 358           struct timespec wakeup_time;
 359
 360           ++idle_thread_count;
 361           gettimeofday (&now, NULL);
 362           wakeup_time.tv_sec = now.tv_sec + optim.gai_idle_time;
 363           wakeup_time.tv_nsec = now.tv_usec * 1000;
 364           if (wakeup_time.tv_nsec >= 1000000000)
 365             {
 366               wakeup_time.tv_nsec -= 1000000000;
 367               ++wakeup_time.tv_sec;
 368             }
 369           pthread_cond_timedwait (&__gai_new_request_notification,
 370                                   &__gai_requests_mutex, &wakeup_time);
 371           --idle_thread_count;
 372           runp = requests;
 373           while (runp != NULL && runp->running != 0)
 374             runp = runp->next;
 375         }
 376
 377       if (runp == NULL)
 378         --nthreads;
 379       else
 380         {
 381           /* Mark the request as being worked on.  */
 382           assert (runp->running == 0);
 383           runp->running = 1;
 384
 385           /* If we have a request to process, and there's still another in
 386              the run list, then we need to either wake up or create a new
 387              thread to service the request that is still in the run list. */
 388           if (requests != NULL)
 389             {
 390               /* There are at least two items in the work queue to work on.
 391                  If there are other idle threads, then we should wake them
 392                  up for these other work elements; otherwise, we should try
 393                  to create a new thread. */
 394               if (idle_thread_count > 0)
 395                 pthread_cond_signal (&__gai_new_request_notification);
 396               else if (nthreads < optim.gai_threads)
 397                 {
 398                   pthread_t thid;
 399                   pthread_attr_t attr;
 400
 401                   /* Make sure the thread is created detached.  */
 402                   pthread_attr_init (&attr);
 403                   pthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
 404
 405                   /* Now try to start a thread. If we fail, no big deal,
 406                      because we know that there is at least one thread (us)
 407                      that is working on lookup operations. */
 408                   if (pthread_create (&thid, &attr, handle_requests, NULL)
 409                       == 0)
 410                     ++nthreads;
 411                 }
 412             }
 413         }
 414
 415       /* Release the mutex.  */
 416       pthread_mutex_unlock (&__gai_requests_mutex);
 417     }
 418   while (runp != NULL);
 419
 420   pthread_exit (NULL);
 421 }
 422
 423
 424 /* Free allocated resources.  */
 425 libc_freeres_fn (free_res)
 426 {
 427   size_t row;
 428
 429   for (row = 0; row < pool_max_size; ++row)
 430     free (pool[row]);
 431
 432   free (pool);
 433 }