htl/pt-dealloc.c

   1 /* Deallocate a thread structure.
   2    Copyright (C) 2000-2024 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 <pthread.h>
  21 #include <stdlib.h>
  22
  23 #include <pt-internal.h>
  24
  25 #include <atomic.h>
  26
  27 /* List of thread structures corresponding to free thread IDs.  */
  28 extern struct __pthread *__pthread_free_threads;
  29 extern pthread_mutex_t __pthread_free_threads_lock;
  30
  31
  32 /* Deallocate the content of the thread structure for PTHREAD.  */
  33 void
  34 __pthread_dealloc (struct __pthread *pthread)
  35 {
  36   if (atomic_fetch_add_relaxed (&pthread->nr_refs, -1) != 1)
  37     return;
  38
  39   /* Withdraw this thread from the thread ID lookup table.  */
  40   __pthread_setid (pthread->thread, NULL);
  41
  42   /* Mark the thread as terminated.  We broadcast the condition
  43      here to prevent pthread_join from waiting for this thread to
  44      exit where it was never really started.  Such a call to
  45      pthread_join is completely bogus, but unfortunately allowed
  46      by the standards.  */
  47   __pthread_mutex_lock (&pthread->state_lock);
  48   if (pthread->state != PTHREAD_EXITED)
  49     __pthread_cond_broadcast (&pthread->state_cond);
  50   __pthread_mutex_unlock (&pthread->state_lock);
  51
  52   /* We do not actually deallocate the thread structure, but add it to
  53      a list of re-usable thread structures.  */
  54   __pthread_mutex_lock (&__pthread_free_threads_lock);
  55   __pthread_enqueue (&__pthread_free_threads, pthread);
  56   __pthread_mutex_unlock (&__pthread_free_threads_lock);
  57 }
  58
  59 /* Confirm deallocation of the thread structure for PTHREAD.  */
  60 void
  61 __pthread_dealloc_finish (struct __pthread *pthread)
  62 {
  63   /* Setting PTHREAD->TERMINATED makes this TCB
  64      available for reuse.  After that point, we can no longer assume
  65      that PTHREAD is valid.
  66
  67      Note that it is safe to not lock this update to PTHREAD->STATE:
  68      the only way that it can now be accessed is in __pthread_alloc,
  69      which reads this variable.  */
  70   pthread->terminated = TRUE;
  71 }