sysdeps/unix/sysv/linux/single-thread.h

   1 /* Single thread optimization, Linux version.
   2    Copyright (C) 2019-2022 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 #ifndef _SINGLE_THREAD_H
  20 #define _SINGLE_THREAD_H
  21
  22 #ifndef __ASSEMBLER__
  23 # include <sys/single_threaded.h>
  24 #endif
  25
  26 /* The default way to check if the process is single thread is by using the
  27    pthread_t 'multiple_threads' field.  However, for some architectures it is
  28    faster to either use an extra field on TCB or global variables (the TCB
  29    field is also used on x86 for some single-thread atomic optimizations).
  30
  31    The ABI might define SINGLE_THREAD_BY_GLOBAL to enable the single thread
  32    check to use global variables instead of the pthread_t field.  */
  33
  34 #if !defined SINGLE_THREAD_BY_GLOBAL || IS_IN (rtld)
  35 # define SINGLE_THREAD_P \
  36   (THREAD_GETMEM (THREAD_SELF, header.multiple_threads) == 0)
  37 #else
  38 # define SINGLE_THREAD_P (__libc_single_threaded_internal != 0)
  39 #endif
  40
  41 #define RTLD_SINGLE_THREAD_P SINGLE_THREAD_P
  42
  43 #endif /* _SINGLE_THREAD_H  */