nptl/lowlevellock.c

   1 /* low level locking for pthread library.  Generic futex-using version.
   2    Copyright (C) 2003-2021 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Paul Mackerras <paulus@au.ibm.com>, 2003.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #include <sysdep.h>
  21 #include <futex-internal.h>
  22 #include <atomic.h>
  23 #include <stap-probe.h>
  24
  25 void
  26 __lll_lock_wait_private (int *futex)
  27 {
  28   if (atomic_load_relaxed (futex) == 2)
  29     goto futex;
  30
  31   while (atomic_exchange_acquire (futex, 2) != 0)
  32     {
  33     futex:
  34       LIBC_PROBE (lll_lock_wait_private, 1, futex);
  35       futex_wait ((unsigned int *) futex, 2, LLL_PRIVATE); /* Wait if *futex == 2.  */
  36     }
  37 }
  38 libc_hidden_def (__lll_lock_wait_private)
  39
  40 void
  41 __lll_lock_wait (int *futex, int private)
  42 {
  43   if (atomic_load_relaxed (futex) == 2)
  44     goto futex;
  45
  46   while (atomic_exchange_acquire (futex, 2) != 0)
  47     {
  48     futex:
  49       LIBC_PROBE (lll_lock_wait, 1, futex);
  50       futex_wait ((unsigned int *) futex, 2, private); /* Wait if *futex == 2.  */
  51     }
  52 }
  53 libc_hidden_def (__lll_lock_wait)
  54
  55 #if ENABLE_ELISION_SUPPORT
  56 int __pthread_force_elision __attribute__ ((nocommon));
  57 libc_hidden_data_def (__pthread_force_elision)
  58 #endif