nptl/sem_wait.c

   1 /* sem_wait -- wait on a semaphore.  Generic futex-using version.
   2    Copyright (C) 2003-2022 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 <lowlevellock.h>       /* lll_futex* used by the old code.  */
  20 #include "semaphoreP.h"
  21 #include "sem_waitcommon.c"
  22
  23 int
  24 __new_sem_wait (sem_t *sem)
  25 {
  26   /* We need to check whether we need to act upon a cancellation request here
  27      because POSIX specifies that cancellation points "shall occur" in
  28      sem_wait and sem_timedwait, which also means that they need to check
  29      this regardless whether they block or not (unlike "may occur"
  30      functions).  See the POSIX Rationale for this requirement: Section
  31      "Thread Cancellation Overview" [1] and austin group issue #1076 [2]
  32      for thoughs on why this may be a suboptimal design.
  33
  34      [1] http://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xsh_chap02.html
  35      [2] http://austingroupbugs.net/view.php?id=1076 for thoughts on why this
  36    */
  37   __pthread_testcancel ();
  38
  39   if (__new_sem_wait_fast ((struct new_sem *) sem, 0) == 0)
  40     return 0;
  41   else
  42     return __new_sem_wait_slow64 ((struct new_sem *) sem,
  43                                   CLOCK_REALTIME, NULL);
  44 }
  45 versioned_symbol (libc, __new_sem_wait, sem_wait, GLIBC_2_34);
  46
  47 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
  48 compat_symbol (libpthread, __new_sem_wait, sem_wait, GLIBC_2_1);
  49 #endif
  50
  51 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  52 int
  53 attribute_compat_text_section
  54 __old_sem_wait (sem_t *sem)
  55 {
  56   int *futex = (int *) sem;
  57   int err;
  58
  59   do
  60     {
  61       if (atomic_decrement_if_positive (futex) > 0)
  62         return 0;
  63
  64       /* Always assume the semaphore is shared.  */
  65       err = lll_futex_wait_cancel (futex, 0, LLL_SHARED);
  66     }
  67   while (err == 0 || err == -EWOULDBLOCK);
  68
  69   __set_errno (-err);
  70   return -1;
  71 }
  72
  73 compat_symbol (libpthread, __old_sem_wait, sem_wait, GLIBC_2_0);
  74 #endif
  75
  76 int
  77 __new_sem_trywait (sem_t *sem)
  78 {
  79   /* We must not fail spuriously, so require a definitive result even if this
  80      may lead to a long execution time.  */
  81   if (__new_sem_wait_fast ((struct new_sem *) sem, 1) == 0)
  82     return 0;
  83   __set_errno (EAGAIN);
  84   return -1;
  85 }
  86 versioned_symbol (libc, __new_sem_trywait, sem_trywait, GLIBC_2_34);
  87
  88 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_1, GLIBC_2_34)
  89 compat_symbol (libpthread, __new_sem_trywait, sem_trywait, GLIBC_2_1);
  90 #endif
  91
  92 #if OTHER_SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_1)
  93 int
  94 __old_sem_trywait (sem_t *sem)
  95 {
  96   int *futex = (int *) sem;
  97   int val;
  98
  99   if (*futex > 0)
 100     {
 101       val = atomic_decrement_if_positive (futex);
 102       if (val > 0)
 103         return 0;
 104     }
 105
 106   __set_errno (EAGAIN);
 107   return -1;
 108 }
 109 compat_symbol (libpthread, __old_sem_trywait, sem_trywait, GLIBC_2_0);
 110 #endif