htl/pt-alloc.c

   1 /* Allocate a new thread structure.
   2    Copyright (C) 2000-2019 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    <http://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 /* Thread ID lookup table.  */
  32 struct __pthread **__pthread_threads;
  33
  34 /* The size of the thread ID lookup table.  */
  35 int __pthread_max_threads;
  36
  37 /* The total number of thread IDs currently in use, or on the list of
  38    available thread IDs.  */
  39 int __pthread_num_threads;
  40
  41 /* A lock for the table, and the other variables above.  */
  42 pthread_rwlock_t __pthread_threads_lock;
  43
  44 /* List of thread structures corresponding to free thread IDs.  */
  45 struct __pthread *__pthread_free_threads;
  46 pthread_mutex_t __pthread_free_threads_lock;
  47
  48 static inline error_t
  49 initialize_pthread (struct __pthread *new)
  50 {
  51   error_t err;
  52
  53   err = __pthread_init_specific (new);
  54   if (err)
  55     return err;
  56
  57   new->nr_refs = 1;
  58   new->cancel_lock = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
  59   new->cancel_hook = NULL;
  60   new->cancel_hook_arg = NULL;
  61   new->cancel_state = PTHREAD_CANCEL_ENABLE;
  62   new->cancel_type = PTHREAD_CANCEL_DEFERRED;
  63   new->cancel_pending = 0;
  64
  65   new->state_lock = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
  66   new->state_cond = (pthread_cond_t) PTHREAD_COND_INITIALIZER;
  67
  68   new->cancelation_handlers = 0;
  69
  70   memset (&new->res_state, '\0', sizeof (new->res_state));
  71
  72   new->tcb = NULL;
  73
  74   new->next = 0;
  75   new->prevp = 0;
  76
  77   return 0;
  78 }
  79
  80
  81 /* Allocate a new thread structure and its pthread thread ID (but not
  82    a kernel thread).  */
  83 int
  84 __pthread_alloc (struct __pthread **pthread)
  85 {
  86   error_t err;
  87
  88   struct __pthread *new;
  89   struct __pthread **threads;
  90   struct __pthread **old_threads;
  91   int max_threads;
  92   int new_max_threads;
  93
  94   __pthread_mutex_lock (&__pthread_free_threads_lock);
  95   for (new = __pthread_free_threads; new; new = new->next)
  96     {
  97       /* There is no need to take NEW->STATE_LOCK: if NEW is on this
  98          list, then it is protected by __PTHREAD_FREE_THREADS_LOCK
  99          except in __pthread_dealloc where after it is added to the
 100          list (with the lock held), it drops the lock and then sets
 101          NEW->STATE and immediately stops using NEW.  */
 102       if (new->state == PTHREAD_TERMINATED)
 103         {
 104           __pthread_dequeue (new);
 105           break;
 106         }
 107     }
 108   __pthread_mutex_unlock (&__pthread_free_threads_lock);
 109
 110   if (new)
 111     {
 112       if (new->tcb)
 113         {
 114           /* Drop old values */
 115           _dl_deallocate_tls (new->tcb, 1);
 116         }
 117
 118       err = initialize_pthread (new);
 119       if (!err)
 120         *pthread = new;
 121       return err;
 122     }
 123
 124   /* Allocate a new thread structure.  */
 125   new = malloc (sizeof (struct __pthread));
 126   if (new == NULL)
 127     return ENOMEM;
 128
 129   err = initialize_pthread (new);
 130   if (err)
 131     {
 132       free (new);
 133       return err;
 134     }
 135
 136 retry:
 137   __pthread_rwlock_wrlock (&__pthread_threads_lock);
 138
 139   if (__pthread_num_threads < __pthread_max_threads)
 140     {
 141       /* We have a free slot.  Use the slot number plus one as the
 142          thread ID for the new thread.  */
 143       new->thread = 1 + __pthread_num_threads++;
 144       __pthread_threads[new->thread - 1] = NULL;
 145
 146       __pthread_rwlock_unlock (&__pthread_threads_lock);
 147
 148       *pthread = new;
 149       return 0;
 150     }
 151 #ifdef PTHREAD_THREADS_MAX
 152   else if (__pthread_num_threads >= PTHREAD_THREADS_MAX)
 153     {
 154       /* We have reached the limit on the number of threads per process.  */
 155       __pthread_rwlock_unlock (&__pthread_threads_lock);
 156
 157       free (new);
 158       return EAGAIN;
 159     }
 160 #endif
 161
 162   /* We are going to enlarge the threads table.  Save its current
 163      size.  We're going to release the lock before doing the necessary
 164      memory allocation, since that's a potentially blocking operation.  */
 165   max_threads = __pthread_max_threads;
 166
 167   __pthread_rwlock_unlock (&__pthread_threads_lock);
 168
 169   /* Allocate a new lookup table that's twice as large.  */
 170   new_max_threads
 171       = max_threads > 0 ? max_threads * 2 : _POSIX_THREAD_THREADS_MAX;
 172   threads = malloc (new_max_threads * sizeof (struct __pthread *));
 173   if (threads == NULL)
 174     {
 175       free (new);
 176       return ENOMEM;
 177     }
 178
 179   __pthread_rwlock_wrlock (&__pthread_threads_lock);
 180
 181   /* Check if nobody else has already enlarged the table.  */
 182   if (max_threads != __pthread_max_threads)
 183     {
 184       /* Yep, they did.  */
 185       __pthread_rwlock_unlock (&__pthread_threads_lock);
 186
 187       /* Free the newly allocated table and try again to allocate a slot.  */
 188       free (threads);
 189       goto retry;
 190     }
 191
 192   /* Copy over the contents of the old table.  */
 193   memcpy (threads, __pthread_threads,
 194           __pthread_max_threads * sizeof (struct __pthread *));
 195
 196   /* Save the location of the old table.  We want to deallocate its
 197      storage after we released the lock.  */
 198   old_threads = __pthread_threads;
 199
 200   /* Replace the table with the new one.  */
 201   __pthread_max_threads = new_max_threads;
 202   __pthread_threads = threads;
 203
 204   /* And allocate ourselves one of the newly created slots.  */
 205   new->thread = 1 + __pthread_num_threads++;
 206   __pthread_threads[new->thread - 1] = NULL;
 207
 208   __pthread_rwlock_unlock (&__pthread_threads_lock);
 209
 210   free (old_threads);
 211
 212   *pthread = new;
 213   return 0;
 214 }