htl/pt-alloc.c

   1 /* Allocate a new thread structure.
   2    Copyright (C) 2000-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   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 <string.h>
  24
  25 #include <pt-internal.h>
  26
  27 /* This braindamage is necessary because the standard says that some
  28    of the threads functions "shall fail" if "No thread could be found
  29    corresponding to that specified by the given thread ID."  */
  30
  31 /* The size of the thread ID lookup table.  */
  32 int __pthread_max_threads;
  33
  34 /* List of thread structures corresponding to free thread IDs.  */
  35 struct __pthread *__pthread_free_threads;
  36 pthread_mutex_t __pthread_free_threads_lock;
  37
  38 static inline error_t
  39 initialize_pthread (struct __pthread *new)
  40 {
  41   error_t err;
  42
  43   err = __pthread_init_specific (new);
  44   if (err)
  45     return err;
  46
  47   new->nr_refs = 1;
  48   new->cancel_lock = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
  49   new->cancel_hook = NULL;
  50   new->cancel_hook_arg = NULL;
  51   new->cancel_state = PTHREAD_CANCEL_ENABLE;
  52   new->cancel_type = PTHREAD_CANCEL_DEFERRED;
  53   new->cancel_pending = 0;
  54
  55   new->state_lock = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
  56   new->state_cond = (pthread_cond_t) PTHREAD_COND_INITIALIZER;
  57   new->terminated = FALSE;
  58
  59   memset (&new->res_state, '\0', sizeof (new->res_state));
  60
  61   new->tcb = NULL;
  62
  63   new->next = 0;
  64   new->prevp = 0;
  65
  66   return 0;
  67 }
  68
  69
  70 /* Allocate a new thread structure and its pthread thread ID (but not
  71    a kernel thread).  */
  72 int
  73 __pthread_alloc (struct __pthread **pthread)
  74 {
  75   error_t err;
  76
  77   struct __pthread *new;
  78   struct __pthread **threads;
  79   struct __pthread **old_threads;
  80   int max_threads;
  81   int new_max_threads;
  82
  83   __pthread_mutex_lock (&__pthread_free_threads_lock);
  84   for (new = __pthread_free_threads; new; new = new->next)
  85     {
  86       /* There is no need to take NEW->STATE_LOCK: if NEW is on this
  87          list, then it is protected by __PTHREAD_FREE_THREADS_LOCK
  88          except in __pthread_dealloc_finish where after it is added to the
  89          list (with the lock held), it drops the lock and then sets
  90          NEW->STATE and immediately stops using NEW.  */
  91       if (new->terminated)
  92         {
  93           __pthread_dequeue (new);
  94           break;
  95         }
  96     }
  97   __pthread_mutex_unlock (&__pthread_free_threads_lock);
  98
  99   if (new)
 100     {
 101       if (new->tcb)
 102         {
 103           /* Drop old values */
 104           _dl_deallocate_tls (new->tcb, 1);
 105         }
 106
 107       err = initialize_pthread (new);
 108       if (!err)
 109         *pthread = new;
 110       return err;
 111     }
 112
 113   /* Allocate a new thread structure.  */
 114   new = malloc (sizeof (struct __pthread));
 115   if (new == NULL)
 116     return ENOMEM;
 117
 118   err = initialize_pthread (new);
 119   if (err)
 120     {
 121       free (new);
 122       return err;
 123     }
 124
 125 retry:
 126   __libc_rwlock_wrlock (GL (dl_pthread_threads_lock));
 127
 128   if (GL (dl_pthread_num_threads) < __pthread_max_threads)
 129     {
 130       /* We have a free slot.  Use the slot number plus one as the
 131          thread ID for the new thread.  */
 132       new->thread = 1 + GL (dl_pthread_num_threads)++;
 133       GL (dl_pthread_threads)[new->thread - 1] = NULL;
 134
 135       __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 136
 137       *pthread = new;
 138       return 0;
 139     }
 140 #ifdef PTHREAD_THREADS_MAX
 141   else if (GL (dl_pthread_num_threads) >= PTHREAD_THREADS_MAX)
 142     {
 143       /* We have reached the limit on the number of threads per process.  */
 144       __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 145
 146       free (new);
 147       return EAGAIN;
 148     }
 149 #endif
 150
 151   /* We are going to enlarge the threads table.  Save its current
 152      size.  We're going to release the lock before doing the necessary
 153      memory allocation, since that's a potentially blocking operation.  */
 154   max_threads = __pthread_max_threads;
 155
 156   __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 157
 158   /* Allocate a new lookup table that's twice as large.  */
 159   new_max_threads
 160       = max_threads > 0 ? max_threads * 2 : _POSIX_THREAD_THREADS_MAX;
 161   threads = malloc (new_max_threads * sizeof (struct __pthread *));
 162   if (threads == NULL)
 163     {
 164       free (new);
 165       return ENOMEM;
 166     }
 167
 168   __libc_rwlock_wrlock (GL (dl_pthread_threads_lock));
 169
 170   /* Check if nobody else has already enlarged the table.  */
 171   if (max_threads != __pthread_max_threads)
 172     {
 173       /* Yep, they did.  */
 174       __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 175
 176       /* Free the newly allocated table and try again to allocate a slot.  */
 177       free (threads);
 178       goto retry;
 179     }
 180
 181   /* Copy over the contents of the old table.  */
 182   memcpy (threads, GL (dl_pthread_threads),
 183           __pthread_max_threads * sizeof (struct __pthread *));
 184
 185   /* Save the location of the old table.  We want to deallocate its
 186      storage after we released the lock.  */
 187   old_threads = GL (dl_pthread_threads);
 188
 189   /* Replace the table with the new one.  */
 190   __pthread_max_threads = new_max_threads;
 191   GL (dl_pthread_threads) = threads;
 192
 193   /* And allocate ourselves one of the newly created slots.  */
 194   new->thread = 1 + GL (dl_pthread_num_threads)++;
 195   GL (dl_pthread_threads)[new->thread - 1] = NULL;
 196
 197   __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 198
 199   free (old_threads);
 200
 201   *pthread = new;
 202   return 0;
 203 }
 204
 205 void
 206 attribute_hidden
 207 __pthread_init_static_tls (struct link_map *map)
 208 {
 209   int i;
 210
 211   __libc_rwlock_wrlock (GL (dl_pthread_threads_lock));
 212   for (i = 0; i < GL (dl_pthread_num_threads); ++i)
 213     {
 214       struct __pthread *t = GL (dl_pthread_threads)[i];
 215
 216       if (t == NULL)
 217         continue;
 218
 219 # if TLS_TCB_AT_TP
 220       void *dest = (char *) t->tcb - map->l_tls_offset;
 221 # elif TLS_DTV_AT_TP
 222       void *dest = (char *) t->tcb + map->l_tls_offset + TLS_PRE_TCB_SIZE;
 223 # else
 224 #  error "Either TLS_TCB_AT_TP or TLS_DTV_AT_TP must be defined"
 225 # endif
 226
 227       /* Initialize the memory.  */
 228       memset (__mempcpy (dest, map->l_tls_initimage, map->l_tls_initimage_size),
 229               '\0', map->l_tls_blocksize - map->l_tls_initimage_size);
 230     }
 231   __libc_rwlock_unlock (GL (dl_pthread_threads_lock));
 232 }