1  /* sem_wait -- wait on a semaphore.  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 <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