1  /* Copyright (C) 2002-2023 Free Software Foundation, Inc.
       2     This file is part of the GNU C Library.
       3  
       4     The GNU C Library is free software; you can redistribute it and/or
       5     modify it under the terms of the GNU Lesser General Public
       6     License as published by the Free Software Foundation; either
       7     version 2.1 of the License, or (at your option) any later version.
       8  
       9     The GNU C Library is distributed in the hope that it will be useful,
      10     but WITHOUT ANY WARRANTY; without even the implied warranty of
      11     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
      12     Lesser General Public License for more details.
      13  
      14     You should have received a copy of the GNU Lesser General Public
      15     License along with the GNU C Library; if not, see
      16     <https://www.gnu.org/licenses/>.  */
      17  
      18  #include <errno.h>
      19  #include <shlib-compat.h>
      20  #include "pthreadP.h"
      21  #include <stap-probe.h>
      22  #include <atomic.h>
      23  #include <futex-internal.h>
      24  
      25  #include "pthread_cond_common.c"
      26  
      27  /* See __pthread_cond_wait for a high-level description of the algorithm.
      28  
      29     A correct program must make sure that no waiters are blocked on the condvar
      30     when it is destroyed, and that there are no concurrent signals or
      31     broadcasts.  To wake waiters reliably, the program must signal or
      32     broadcast while holding the mutex or after having held the mutex.  It must
      33     also ensure that no signal or broadcast are still pending to unblock
      34     waiters; IOW, because waiters can wake up spuriously, the program must
      35     effectively ensure that destruction happens after the execution of those
      36     signal or broadcast calls.
      37     Thus, we can assume that all waiters that are still accessing the condvar
      38     have been woken.  We wait until they have confirmed to have woken up by
      39     decrementing __wrefs.  */
      40  int
      41  __pthread_cond_destroy (pthread_cond_t *cond)
      42  {
      43    LIBC_PROBE (cond_destroy, 1, cond);
      44  
      45    /* Set the wake request flag.  We could also spin, but destruction that is
      46       concurrent with still-active waiters is probably neither common nor
      47       performance critical.  Acquire MO to synchronize with waiters confirming
      48       that they finished.  */
      49    unsigned int wrefs = atomic_fetch_or_acquire (&cond->__data.__wrefs, 4);
      50    int private = __condvar_get_private (wrefs);
      51    while (wrefs >> 3 != 0)
      52      {
      53        futex_wait_simple (&cond->__data.__wrefs, wrefs, private);
      54        /* See above.  */
      55        wrefs = atomic_load_acquire (&cond->__data.__wrefs);
      56      }
      57    /* The memory the condvar occupies can now be reused.  */
      58    return 0;
      59  }
      60  libc_hidden_def (__pthread_cond_destroy)
      61  versioned_symbol (libc, __pthread_cond_destroy,
      62  		  pthread_cond_destroy, GLIBC_2_3_2);