nptl/lowlevellock.c

   1 /* low level locking for pthread library.  Generic futex-using version.
   2    Copyright (C) 2003-2023 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 <sysdep.h>
  20 #include <futex-internal.h>
  21 #include <atomic.h>
  22 #include <stap-probe.h>
  23
  24 void
  25 __lll_lock_wait_private (int *futex)
  26 {
  27   if (atomic_load_relaxed (futex) == 2)
  28     goto futex;
  29
  30   while (atomic_exchange_acquire (futex, 2) != 0)
  31     {
  32     futex:
  33       LIBC_PROBE (lll_lock_wait_private, 1, futex);
  34       futex_wait ((unsigned int *) futex, 2, LLL_PRIVATE); /* Wait if *futex == 2.  */
  35     }
  36 }
  37 libc_hidden_def (__lll_lock_wait_private)
  38
  39 void
  40 __lll_lock_wait (int *futex, int private)
  41 {
  42   if (atomic_load_relaxed (futex) == 2)
  43     goto futex;
  44
  45   while (atomic_exchange_acquire (futex, 2) != 0)
  46     {
  47     futex:
  48       LIBC_PROBE (lll_lock_wait, 1, futex);
  49       futex_wait ((unsigned int *) futex, 2, private); /* Wait if *futex == 2.  */
  50     }
  51 }
  52 libc_hidden_def (__lll_lock_wait)
  53
  54 void
  55 __lll_lock_wake_private (int *futex)
  56 {
  57   lll_futex_wake (futex, 1, LLL_PRIVATE);
  58 }
  59 libc_hidden_def (__lll_lock_wake_private)
  60
  61 void
  62 __lll_lock_wake (int *futex, int private)
  63 {
  64   lll_futex_wake (futex, 1, private);
  65 }
  66 libc_hidden_def (__lll_lock_wake)
  67
  68 #if ENABLE_ELISION_SUPPORT
  69 int __pthread_force_elision;
  70 libc_hidden_data_def (__pthread_force_elision)
  71 #endif